General Technical Report
Constant-Effort Mist Nets and Banding
The capture of birds in nets can give the biologist an insight into the health and demographics of the population of the birds being studied. For instance, the proportion of young birds captured in mist nets has been shown to be a good measure of the productivity of birds during the previous few weeks (Baillie and others 1986). The sex ratio of a population can be used to assess the species differential survivorship the previous year and the ability of the population to increase. The mist net capture rate gives a measure of the number surviving during the previous winter. The marking of individuals gives the biologist insight into degree of dispersal between different habitats and survivorship between years (e.g., Peach and others 1991). Finally, weight, when compared to measures of body size such as wing length, can give a measure of individual fitness.
Mist nets have been used for a long period to capture birds. Recently they have been used to monitor populations. Although some have used them to assay population size (e.g., Karr 1981), for most species, censuses are the best method for this, as netting provides relatively fewer data points per unit time. Netting, however, is the method of choice to provide information about the various attributes of the population, for instance, age and sex ratios and physiological condition.
Over the years numerous aids have been developed for field workers, with an emphasis on capture techniques and data taking (e.g., Baldwin 1931, Bub 1991, Lincoln 1947, Lincoln and Baldwin 1929, Lockley and Russell 1953, McClure 1984). O.L. Austin introduced mist nets to North American biologists in 1947 (Keyes and Grue 1982), and he, Low (1957), and Bleitz (1957) were all pioneers in their use.
The procedure detailed below is essentially identical to the Constant Effort Sites (CES) Scheme of the British Trust for Ornithology (Baillie and others 1986). The standards of operation are also identical to those of the Monitoring Avian Productivity and Survivorship Program (MAPS) (DeSante 1992a). We suggest the use of a series of mist net arrays, as in the British program, to be operated on 10 to 12 intervals during the breeding season, coupled with point count censuses. These data will provide an index of adult population size and changes at each station. The proportion of young birds in the catch will provide a measure of post-fledgling productivity. And finally, between-year recaptures can provide a sensitive measure of adult survivorship and recruitment. With these data, managers will have information on the possible causes of landbird declines or their remedies.
The monitoring of populations with mist nets is no more complicated than other techniques, but placement and operation should be done rather uniformly; thus we present below more details about this method than about others.
Operating a capture array of mist nets is a complex undertaking, but very rewarding. Much useful information can be gained from reading Bleitz (1970), Keyes and Grue (1982), or McClure (1984). We outline below some guidelines for operation of nets and their placement (fig. 1).
Figure 1An idealized capture station of about 40 acres (16 ha) set in an area of more than 250 acres of habitat A. Nine census points are set at uniform spacing of about 150 m to estimate population levels. Ten net locations are placed in sites where high capture rates are likely, along a stream, near a spring, and other areas where vegetation is dense, in order to monitor population and demographic parameters.
A field crew of two people can usually set up and monitor an array of 8-12 mist nets quite easily. We suggest 10 as an appropriate number. If the biologists are especially skilled, or the bird density quite low, a few more nets may be operated. However, if too many nets are established in an array early in the season when capture rates are relatively low, the likely influx of post-breeding birds later in the season, in July and August, may severely tax the crews resources.
Distance between nets is a very important consideration because of the effect of net dispersion on the precision of data from capture-recapture analyses. In order to increase the probability of capturing a bird banded the previous year, one should place the nets as far apart as possible, thus intersecting the most territories. However, it is absolutely critical that nets also be close enough to each other that a person can visit all net locations in a maximum of 10-15 minutes walking, preferably less, if no birds are caught. On flat, level terrain, this array would be about 0.5-0.6 miles (800-1000 m) in length. If 10 nets are placed in a circle or rectangle, this would allow about an average of 75-100 m between nets, and would cover approximately 5-10 ha. In steep or rough terrain, nets should be closer, and the area covered less. In all cases, nets should be spread out as uniformly as possible.
Nets should be placed at the same location and orientation for all 10-day intervals in each year and preferably between years. In the event the vegetation changes between years at a given location, the nets will measure this change, rather than changes in population of the birds. For this reason, care should be exercised in placing nets in locations where the vegetation will remain relatively stable through the life of the study. For example, successional changes, for instance, from a clear-cut to pole-sized trees over 10 years, would be unacceptable for a site. However, when the changes over a decade would be much less marked, the site would be permitted. If, due to unforeseen circumstances, the vegetation is changed markedly at one or two net locations of an array, the nets can be moved to locations with similar vegetation to allow better between-year comparisons. This should be a last resort, and only done after consultation with knowledgeable participants in the program.
Although few problems arise from placement of census points in areas of relatively high human impact, capture arrays must be located with more care. In some areas nets can be left in place (but closed) between capture days if the chance of encounter by visitors is extremely low. In most areas, it is advisable to rig the nets to allow easy removal at the close of a days effort.
Baiting, artificial water, or taped vocalizations should not be used at any time to attract birds to the nets.
The best locations for the nets are usually on an edge of a habitat. Examples of edges include the boundary between a forest and a field, the boundary between two forests types (e.g., an upland pine and a pine/alder association in a valley), brushy portions of wooded areas, at the edge of a pond, and along a riparian corridor. Especially productive are areas where a habitat type has a narrow section, for instance a hedgerow, that narrows at a gate or where a natural gap funnels the vegetation along a watercourse. Birds, especially shrub species, will naturally be funneled into a net at that spot. Observations of bird movements will often suggest appropriate net locations.
The highest rate of capture is usually found in wetter areas within a given habitat type. If at all possible, natural running or pooled water should be available throughout the summer in the capture array, as it will draw birds from the immediate area. An array aside a major watercourse with a well-developed and wide riparian corridor will tend to monitor this habitat, but will also monitor the surrounding habitats. In many regions of the country, the riparian zone is the only place where sufficient numbers of birds can be captured.
The major goal of a mist net array is to capture birds, not to monitor the birds of a specific habitat. Census methods or nest search are more appropriate for this. An array set in a uniform habitat, such as an old-growth stand of coniferous trees, will usually catch relatively few birds, even if located along a watercourse in that habitat. There are possible exceptions to this, such as eastern deciduous forests (T. Sherry, pers. comm.).
A reasonable goal for capture rate is approximately two birds per net per day. This would result in the capture of approximately 200 or more birds during the season. Typically, the capture rate in the breeding season will be high during the first 10-day period, decline thereafter, and usually increase again during post-breeding dispersal, in July and August in temperate North America.
Erecting and Operating Nets
In order to operate nets properly, the trammels (the horizontal shelf strings that support the net) should be taut horizontally. Except with 6-m nets, this usually involves the use of tie cords bracing the pole upright. These can be arranged at 120° angles to the net, with one end secured to the pole and the other to nearby rocks, bushes, or stakes. When operated, the netting material should not be stretched apart to its full extent, but should allow some slack between the trammel lines; otherwise birds will bounce off the tight net.
If the habitat is higher than the typical net height of 2.5 or 3 meters above the ground, a stacked net can be considered. Although some birds may be missed, it is better to use single nets, rather than to stack them one above another, unless a particular location has a great abundance of birds. Even canopy-dwelling species invariably spend at least some time at lower levels, whether to nest, take water, or forage. The additional time spent putting up a stacked net can usually be better employed by establishing another net in the array. McClure (1984) describes several plans to stack nets; the simplest is to use a strong metal pole, perhaps 8-10 feet long, such as metal electrical conduit pipe. Connect two lengths together with a sleeve (a 10-cm section of conduit slipped over a 20-cm long pipe and glued in place), and tether the pole with a rope. The net can be easily lowered and raised using this method.
For single nets, we suggest the following simple method of putting them in place, adapted from Dennis P. Vroman (pers. comm.). Clear all vegetation from a net lane 2 m wide to prevent vegetation from becoming entangled in the net. Drive one piece of 1-m by 3/8-inch piece of steel reinforcing bar (rebar) into the ground with a small hand sledge hammer at one end of the net lane on a slight backward angle to the net. Insert a 5-foot section of sawn 10-foot, 0.5-inch or larger, galvanized steel conduit over the rebar. Repeat at the other end of the net lane.
A single net can be kept on a round metal spool (used to hold bulk electrical wire), with a 6.5-inch diameter rim and 3.5- to 4-inch long axle or shaft. Place the loops of the net over the top of the upright conduit; then unroll the net towards the second pole, being careful to keep the loops in order. A second 5-foot section can be placed on each pole in a conduit connector or a sleeve atop the first conduit to allow the net to be fully opened.
When a net is to be closed, it should be spun to keep it from unraveling. To do this most effectively (preferably with two people from both ends simultaneously), leave the topmost trammel separated from the others on the pole, and spin the net on the lower trammels into a tight roll. Then quickly bring the top trammel down atop the roll to keep it from unraveling. This will allow the net to be opened much more quickly than if the net had been spun around all the trammel lines.
To roll up the net, keep all the support cords together and centered on the axle as the net is rolled up to allow easy unrolling. Use a rubber band to hold the loops in place at the end of the rolled net. Poles and rebar can be hidden under vegetation near the net location to save set-up time.
Nets are also commonly put in cloth bags. To take down the net, it is rolled up on small folds and put into the bag, as the biologist moves from one end towards the other.
Net Specifications and Maintenance
A variety of net types can be purchased, but we strongly suggest that the same type be used throughout the life of the study. The net color should be black in forest or brush habitats. The net mesh should be either 30 mm or 36 mm in stretched diameter. The larger net catches more thrush-sized birds, but smaller birds can become more severely tangled. Nets 12 m in length are preferred, although in certain sites a half-net of 6 m long can prove useful. (If a 6-m net is used, its use for one hour equals a half net-hour.) In addition, some suppliers offer extra-full nets that provide more capture area. They also offer tethered nets that are resistant to bunching by the wind because they are fastened to the trammels. If a nontethered net is obtained, it can easily be tethered by placing drops of a liquid cement along the top trammel.
A net should be replaced when it fades badly or becomes degraded by the sun so that it breaks very readily. A net can be tested by putting two fingers into the net and gently parting them. Nets sustain damage from branches, misuse, large birds, and from the rare occasions when a badly tangled bird must be cut out of the netting. The life can be prolonged by repairs with a strong black nylon twine or thread. Holes should be repaired promptly, or the net replaced, as they affect the efficiency of capture, and make it difficult to figure out how to extract a bird.
Operation of Nets
To minimize variability and make comparisons from different locations, standardization of the number of nets and the number of hours nets are operated has long been advocated. It is extremely important that nets be operated on the same schedule between years, so as to allow direct comparisons. A standard net is considered to be 12 m long and 2.5 m high. For calculating effort, one standard mist net operated for one hour is a net-hour. Two nets stacked atop one another would be considered two nets, although one net location. If operated for one hour, they would total two net-hours.
Although there are methods of compensating for varying number of nets operated in different time periods (Ralph 1976), these are best implemented during migratory periods when there is a high turnover of individuals between days. During the breeding season, when populations are more stable, it is best to operate nets on as regular a schedule as possible. This includes the number of nets, the number of hours, the time of day, the number of days, and the number of days between operations.
We recommend that biologists use the Record of Net-Hours form (fig. 2). The data are recorded on a daily basis, as follows:
- State or provinceThe 2-column code for each.
- RegionAn 8-column code, designated by the investigator. Often, the name of the USGS quad, a prominent landmark, or a nearby town will provide the best code name.
- StationA 4-letter code for the station that contains the mist net array.
- Net locationPlace a 2-column number identifying each net location. Most arrays will have no more than 10 locations, and thus would be numbered 1-10.
- Number of netsThis number is usually one, but if a stacked net is used, or if a net is within 10 m of another, they are considered the same location, and the number of nets is entered here.
- Month and dayOne line for each day of operation, but if a net location is operated for more or less time than the other nets, it should get a line to itself.
- Open and close timesUsing the 24-hour clock, record the time of starting to open and the time of starting to close the nets.
- Hours openCalculate the number of hours open to the nearest tenth of an hour (e.g., 4 hours, 20 minutes is 4.3 hours).
- Number of net-hoursMultiply the number of nets by the hours open, and enter here.
- Total net-hoursFor each day, total the number of net-hours.
Figure 2The Record of Net-Hours, for recording and summarizing net-hours.
Time of Day and Number of Checks
Nets should be opened within 15 minutes of local sunrise and operated for a minimum of 4, and preferably 6, hours per day. Nets should be checked every 45 minutes (more often in inclement or very hot weather) and absolutely not more than once each hour. That is, the net round should begin no longer than 45 minutes after the start of the previous round. Nets should be opened in the same order each day, and closed in the same order that they were opened. It is very desirable that the number of hours for each net location should be the same for all 10-day intervals and for all years. Each station should be operated once per 10-day monitoring interval throughout the breeding season. We recommend that arrays be run no more than once per 10-day interval. Running arrays more than twice per interval greatly lowers capture probability per net hour. If sufficient time is available, it is far more productive to set up another array, rather than increasing effort at a single station.
When To Close Nets
The nets should not be operated in rain, wind, and extreme heat. If already open when these conditions occur, they should be closed, because precipitation is heavy enough for the birds feathers to become wet enough to lose their insulation. Strong winds can cause severe tangling. In general, a steady wind of more than 10 mph or occasional gusts to more than 15 mph should be watched carefully for their effect on netted birds, and the nets should be closed if necessary. Finally, in situations with excessive heat and direct sunlight with little wind, netted birds can quickly overheat and die. On such hot days, birds should not remain in an exposed net for more than 15 minutes.
A certain amount of mortality may occur whenever wildlife is handled or trapped. However, mortality rates in most netting projects usually approach zero, and generally average less than 1 percent when mortality does occur. If mortality consistently occurs in nets, or exceeds an average of 1 percent, it is likely that birds are not being processed quickly enough, probably during their removal from the nets. Under these circumstances, scrutinize closely the criteria for closing nets and the expertise of the people running the station.
Removing Birds from Nets
Below we suggest some methods for extracting birds from mist nets. The methods are used by most netters, were derived from ideas of Shreve (1965), and were later modified and augmented by Ralph (1967, 1988). Practice and careful review of these techniques are essential. Most importantly, be careful. The life and health of the birds are of primary concern.
As you work on a badly tangled bird, it is important to remember that the bird can usually be backed out easily, unharmed, in the direction from which it entered the net. You must first take the time necessary to figure out exactly how the bird went into the net. Observe carefully from which side the bird entered the net, and between which trammels it went, in order to find the opening of the pocket the bird made. Do not just grab the bird, tempting as it may be. Start on the side of the net which the bird entered; part the trammels and netting loosely, and look into the pocket caused by the weight of the bird. Because the tail is the last to enter, look at its position to get a clue about how the bird entered the net. Back the bird out the way it went in, step by step. A light touch is the most important prerequisite for all methods. After determining where the bird entered, several standard procedures are used for removing birds, but different species and different problems will require some improvisation.
We describe the various methods used to remove birds from nets below. No one method will suffice for all birds, because each bird flies into a net differently. Combinations of methods will often be necessary. In all methods it is often desirable to know where the strands of net are amongst the birds feathers. This knowledge can help you decide where to move your fingers next. By far the best method is to pull gently at the exposed netting and see where feathers move on the bird. This will tell you where the net strands are binding, leading to quicker removal.
Body Grasp Method
This method has recently been used by some stations, and it has been found to surpass other methods in ease of learning, reduced injury to the birds, and speed of removal. About 9 of 10 birds can be removed with this method.
- Find out from which side of the net the bird entered. Find the opening of the pocket caused by the weight of the bird.
- You have three choices at this point. (1) If the birds body is accessible, without any netting in the way, and the net free of the back and head, just put the bird into the banders grip, with your palm against its back, your index and middle fingers on either side of the neck, the left wing held with your thumb, and the other fingers curled around the body and the right wing. Then proceed to step #7 below. (2) If the net is tangled around the head and wing, just slip your fingers over the body and under the wings. This usually involves your thumb around the breast and your fingers over the birds back, and down over its sides and under the wings and carefully around the curve of the body. (3) If the body is too tangled to be available for a body grasp, then one of the other methods below must be used.
- With the body now firmly secured, back the body out of the net to expose at least the bend of one of the wings. Then, remove the net from the wings. Flick net threads from the bend of the wings, working from the underside. Generally your thumb should be placed under the thread(s) on the underside of the wing and your forefinger placed on the outer bend of the wing as a fulcrum to flick the thread over. Often at this stage it is helpful to pull gently on the exposed portions of the still tangled threads in order to free them or to see where they are caught.
- When one wing is free, slip your fingers over the now-exposed wing, securing it against the birds body. Then, pull remaining loops from around the neck, working from the back of the head forward, in the manner of removing a T-shirt.
- Remove the net from the other wing, as above.
- The bird should now have gradually been put into the banders grip.
- Pull the bird up and away from the net, and it will usually free its own feet in an effort to fly. If the toes are caught, untangle them by pulling strands gently. You will notice that if the heel joint is straightened out, the birds toes have a tendency to relax, so that the netting can be more easily removed. If the bird is clutching the net firmly, extract the feet by (1) first freeing the opposable toe (the thumb) by sliding the threads over it and lifting it away from the other toes; (2) with the fingers, straightening the other three toes out; and (3) sliding the netting over the toes with repeated strokes.
This method, when administered with a nimble hand and a light touch, is very easy on the bird because the only firm contact is on the sides of the neck. It is also a time saver, because feet untangle themselves. The method works best with a recently caught bird that has had little time to entangle itself, but is applicable to most birds.
Feet First Method
The original, and perhaps still the most widely used method, is somewhat slower but is usually the way that beginners are taught. Its main disadvantage is that it requires holding the legs, sometimes causing injury or breakage. It involves the following steps:
- As before, find the side of the net the bird entered.
- If you (the bander) are right-handed, grasp both tibiae (the tibia is the feathered part of the leg above the bare tarsus) from the rear of the bird using your left hand so that your fingers point towards the birds head. The bird should be upside down in the net when you have your grip.
- Put your index finger between the tibiae, and press your thumb against the birds right tibia and your middle finger against the left tibia. This leaves your right hand free to remove net strands from the entangled legs and feet.
- Most importantly, make certain that all threads are pulled down and off tibiae and thighs below the heel joint, the prominent joint between the tibia and tarsus. These threads are sometimes high up on the thigh at the flank.
- Untangle the toes by the method described in the body grasp method above.
- Pull the bird up and away from the net, still holding the bird upside down by the feathered tibiae, above the bare tarsus. Flick net threads from the bend of the wings, working from the underside. Generally the thumb should be placed under the thread(s) on the underside of the wing and the forefinger placed on the outer bend of the wing as a fulcrum to flick the thread over. Often at this stage it is helpful to pull gently on the exposed portions of the still tangled threads in order to free them or to see where they are caught.
- When both wings are free, pull remaining loops from around the neck, working from the back of the head forward. Be sure to secure the bill by placing the thumb against the tip while pulling the net over the head in order to protect the delicate neck.
A third method requires a little practice but is applicable to almost every situation:
- As always, determine the side of the net entered.
- Grasp the left (or right) leg above the tarsus and release the foot.
- Release the left (or right) wing; release the head, then the other wing. Grasp the bird normally with the banders grip. Finally, free the right foot.
This method requires an experienced feelthe bird is rolled over and released in order of foot, wing, head, wing, and foot. This method is especially recommended when one of the legs is particularly badly tangled. Work so as to free that leg last.
Once the birds are removed from the nets, put each individual in a separate, small cloth bag, and transport to the processing site. It is probably best to have a central processing site, rather than to process birds at each net as they are captured, because: (1) a biologist rapidly circulating around the nets can better monitor the captures, in case of an influx of birds that might necessitate shutting down some nets temporarily; and (2) it lessens the disturbance in the vicinity of the nets. Further, if processing becomes delayed, it is always preferred to have the birds out of the nets and stored in bags. Bags should be made from opaque cloth, and sewn so that the seams (and possible loose threads that can catch toes) are outside. Hang bags from hooks or branches to prevent them from being stepped on, and out of direct sunlight. They should be washed often.
Birds should be released at the processing site except for females (indicated by a brood patch) and dependent juveniles (indicated by a frizzy appearance and a growing tail). They should be released at the point of capture.
Recaptures provide the most important data in a constant-effort mist netting program. We suggest, if some birds have to be released without processing, that recaptures have a much higher priority for processing than unbanded birds. If birds have to be released without complete processing, we suggest that the following be regarded as the priorities, in order: (1) band number (if a recapture); (2) species; (3) age (usually involves skulling, or diagnostic plumage characters); (4) new band number (if previously unbanded); (5) sex; and (6) other measurements or data. Please notice that the species and age are the two variables which are considered absolutely critical. If these are not accurately and completely recorded, the time and money spent in the monitoring has minimal value to the objectives.
Tongue Caught in Net
The mouth structure of birds, especially thrushes, thrashers, and woodpeckers, allows net threads to catch behind the tongue. While the birds head is held between your index and middle finger, your third and fourth fingers and thumb can hold the net near the side of the mouth and relieve pressure on the tongue by pulling the net backward along the side of the head. A pencil, crochet hook, or a sharp twig can be manipulated with your free hand to lift the thread from behind the cleft of the tongue. Until one becomes deft at releasing the tongue in this manner, a small pair of a scissors is invaluable. Usually, clipping a single strand of mesh will do the trick.
Badly Caught Birds
As a last recourse, to remove a strand from a tongue, or to rapidly extract a bird in distress it is sometimes necessary to cut a few threads with a scissors, a stitch ripper (sewing tool that cuts threads along seams), or a sharp knife. The most rapid method is to find an area with few (or only one if possible) layers of netting. Clip as few strands as possible, just enough to bring the bird through the net. Then free the bird in the normal manner. It should be very rare to need to cut more than three strands. Before releasing such a bird, look carefully to ensure that no net remains on the bird.
One of the first steps a biologist must take to make the capture work more meaningful is to properly record the data presented each time that a bird is caught. Much of the following was extracted from Pyle and others (1987) and Ralph (1967, 1988). The identification guide by Pyle and others (1987) should be included in all netting kits.
At each net location, we suggest that the Location and Vegetation Form (fig. 15, discussed in detail below) be filled out. The Location information on the first three lines of the form is vital to data base management.
For each individual captured or recaptured, we recommend that the following data be recorded. In addition to date, time, and location, it is imperative that the species be accurately identified. It is also vital that the age and the sex of the birds be determined. We highly recommend that determining the amount of skull pneumatization be a top priority, as essentially all analyses depend upon accurate ageing. Age and sex determinations are generally complicated by the highly variable nature of size, plumage, and molt patterns in each species. We recognize that a certain percentage of individuals cannot be reliably aged, sexed, or identified with any one or even all of the published criteria. Remember that with age and sex it is better to be cautious than inaccurate. If the bander is unsure of an age/sex class, we recommend that the record be conservative, by recording the age or sex as unknown, and separately noting which class seems likely. By using the skull pneumatization and the literature carefully, determinations can be made with above 99 percent confidence. Information on how the bander aged and sexed the bird can be used to screen improperly processed birds. We also highly recommend that the breeding condition of adults, the extent of juvenal plumage and molt, and the wing chord also be recorded.
For the various attributes below we suggest a letter or numeric code. We strongly suggest that whatever codes are used at a station should be used consistently between years, or certainly within a year. Alpha (letter) codes have the advantage of being mnemonic in nature, increasing accuracy. Numeric codes have the advantage of retaining the order of progression from small, none, or few, to large or many.
The first plumage (subsequent to the natal down) acquired by the nestling and retained by the juvenile fledgling is called the juvenal plumage (note the difference in spellings). The body feathers of this plumage are replaced during the first prebasic molt, which almost always occurs within three months of fledging and usually takes place on the breeding grounds. Juveniles are readily aged by many criteria and are generally sexually indistinguishable by plumage. The juvenal plumage is usually more streaked or spotted than that of the adult, and juveniles will often have wing bars where the adult has none. Juvenal feathers also have a more loosely structured contour (fig. 3), most evident in the feathers of the nape, back, and undertail coverts. In addition, many nestling characteristics are evident in young juveniles which can also be helpful in separating them from adults. The gape of nestlings and early juveniles is swollen and more brightly colored than that in adults, and the inside of the mouth is also brighter in tone, or paler in hue, or both, in juveniles than in adults. Several characters useful for separating first-year birds from adults can be applied to juveniles. In particular, summer adults in alternate (breeding) plumage should show very worn flight feathers while those of juveniles should be relatively much fresher. And, of course, the pneumatization process is just beginning in juveniles, whereas it should be complete (or nearly so) in adults. Finally, eye color is useful for separating juveniles of many species, being generally grayer and paler in juveniles and redder and darker in adults. In summary, biologists should have no trouble with the separation of juveniles from adults during the summer months, when all criteria are used.
Figure 3The contrast between juvenal and nonjuvenal body feathers. The differences are most apparent with undertail coverts and feathers of the nape and back. Taken from Pyle and others (1987).
In most passerine species, however, birds in juvenal plumage cannot be reliably sexed by in-hand criteria alone. Only in a few species, in which differences occur in the color pattern of the flight feathers, can juveniles be sexed by plumage.
As juvenile birds go through their first molt, normally in the fall, they assume a plumage that is often similar to that of adults, especially to that of the adult female in sexually dimorphic (having a male and female plumage) species. Inspecting the skull is now recognized as being the most reliable technique for ageing these birds.
The various age codes suggested below follow, for the most part, the system used by the U.S. Fish and Wildlife Bird Banding Laboratory and the Canadian Wildlife Service Bird Banding Office, as listed in the North American Bird Banding Manual (CWS and USFWS 1991). The system is based primarily on the calendar year. Following are the age designation, the alpha code used by the Services, a suggested one-letter abbreviation (or optional numeric code) for purposes of this handbook (where different from the Services code), and a definition of the age class.
Unknown (U or 0). Age cannot be determined with absolute confidence.
Local (L or 4). A young bird incapable of sustained flight.
Hatching Year (HY) (H or 2). A bird in its juvenal or first basic plumage during its first calendar year (i.e., from its fledging until December 31 of the year that it fledged).
Second Year (SY) (S or 5). A bird in its second calendar year (i.e., January 1 of the year following fledging through December 31 of the same year).
After Hatching Year (AHY) (A or 1). A bird in at least its second calendar year. This code is more significant after the breeding season, when it implies an adult. Before the breeding season, it essentially means unknown (either SY or ASY).
After Second Year (ASY or 6) (O [older]). An adult in at least its third calendar year (i.e., a bird in at least the year following its first breeding season and second prebasic molt). A bird known to be in its third year, or older, should be indicated by O, and a note should be made in the Notes columns.
Determining the amount of skull pneumatization, also known as ossification, is the best method of ageing most species of birds during the summer and fall months and, for some species, is proving useful through the early winter and even into spring. The importance of this method cannot be understated. If you take only one datum besides species, skull pneumatization is quite probably the next most important.
This technique came into common usage in the late 1960s. Biologists are strongly urged to become proficient at skulling and to skull most passerine species throughout the year. When a fledgling passerine leaves the nest, the section of the skull overlaying the brain (frontals and parietal) consists of a single layer of bone. From fledging until the bird is four to 12 months old (depending mostly on the species), a second layer of bone develops underneath the first. The two layers are then separated slightly by spaces or air pockets and joined by small columns of bone. This process is called skull pneumatization.
The pattern generally follows one of the two progressions illustrated in figure 4, but may show other variations. Smaller species tend to show the peripheral pneumatization pattern, and larger species the median line pattern. Individuals of certain species may show either pattern, however, and the exact shapes of the unpneumatized areas or windows will also show substantial individual variation.
Figure 4The two common patterns of skull pneumatization, from a very young bird (a), to a completely pneumatized bird (e). Taken from Pyle and others (1987).
Any passerine found with a partially pneumatized skull (fig. 4a-c) can be reliably aged as a hatching year bird, with the exception perhaps of occasional summer or early fall birds with small windows (fig. 4d). In most North American passerine species, the skulls of the earliest hatching year birds become completely pneumatized in October and November, and the latest birds become complete between November and January, but for purposes of this monitoring effort during the breeding season, all hatching year birds will have incomplete pneumatization.
In some (perhaps many) species, small unpneumatized windows may normally be retained until spring and even early summer. This is most commonly seen in the longer distance migrants such as certain flycatchers, swallows, thrushes, and vireos. Birds with windows greater than one millimeter in diameter (fig. 4d) are probably reliably aged as Second-years through June of their second year. Birds with smaller windows are not necessarily in their hatching year, because some small proportion (probably less than 1 percent) of individuals will never show complete pneumatization. Birds with small windows in July and August are most likely to be advanced young of that year.
The Process of Determining the Extent of Skull Pneumatization
Unpneumatized areas of the passerine skull usually appear pinkish or dull reddish, whereas pneumatized areas appear grayish, whitish, or pinkish-white, with small white dots indicating the columns of bone. The color or contrast between these two color patterns, or both, can usually be seen through the skin of the head, especially after the head has been wetted to allow parting of the feathers, and to make the skin more transparent.
To skull a passerine, start by holding the bird in the position shown in figure 5. This hold facilitates skulling because the skin can more readily be moved around the skull, allowing a large area of the skull to be viewed through a small area of skin. In order to see the skull, the feathers need to be parted such that a small opening of bare skin is created. This can be accomplished without wetting the feathers, but is much more easily done if a small amount of water is applied to the head (do not apply detergent or alcohol solutions). During cold weather, the few drops of water used to make the skin more transparent should have no effect on the birds ability to maintain its temperature. If there is concern about this, simply put the bird out of the wind in a dry bag for a few minutes before releasing it.
Figure 5Two good holds for skulling a bird. It is best to look to the side of the mid-line of the skull. Taken from Pyle and others (1987).
It is usually easiest to part the feathers by running your thumb or finger forward over the crown, against the direction in which the feathers lie, and then moving the feathers off to each side. In the summer and early fall, when most young birds are just beginning the pneumatization process, it is good to start at the rear and the side of the skull and work up towards the crown. Later in the fall, the parting should be made higher up on the crown (in the areas just above and behind the eyes), where the last unpneumatized windows usually occur. With thicker-skinned birds, one can improve viewing by parting the feathers on the side of the head or neck (where the skin is more transparent) and moving the skin up to the crown. When the skulling process is finished, the feathers can be smoothed back into place.
It is usually best to hold the bird under a fairly strong lamp or in indirect sunshine to achieve the best lighting conditions for viewing. Very bright light often creates a glare off the skin. It is often helpful to move the head around, because different angles of light can make it easier to see through the skin. We strongly recommend using a magnifying device such as a visor that slips over your head.
Move the skin back and forththe spots will be stationary, and thus visible. If the tiny white dots are not visible, one is not properly viewing the skull, or the bird is a very young juvenile with an entirely pinkish skull. Seeing a boundary between whitish and pink areas is not enough, because one might be seeing only bone structure unrelated to pneumatization. Start looking at the skull at a point at its base and slightly to one side. Continue looking forward until just halfway between the eye and the top of the crown. If at no point the dots disappear and are replaced by a clear pink area, the skull is fully pneumatized. Because the pneumatization usually proceeds centripetally and anteriorly, be sure to examine the area between the eyes of all birds with pneumatized skulls, to make sure that they are not advanced immatures.
Also look for entirely pinkish skulls in very young birds (fig. 4a) in June-July and for contrasts between the pneumatized and unpneumatized areas in older birds (most frequently after August). Small windows (fig. 4d) should be carefully looked for at all times.
Any of several factors may make it difficult or impossible to see the pneumatization of the skull. These include: the skin of the head being too thick; large amounts of fat in the skin during fall migration and winter; and dark, or otherwise opaque, skin (especially in molting or injured birds). It is especially difficult to see the pneumatization of the skull in molting birds, because of the thickening and the excessive flaking of the skin.
We suggest codes for categories of skull pneumatization. Because the critical differences are often in the 0-5 percent or 95-100 percent categories, care should be taken. It can make a great deal of difference in evaluating the age during the breeding season to know that a skull had only small windows (e.g., 98 percent pneumatized) and could have been either a second-year bird or perhaps a young bird, as opposed to one that was perhaps 70 percent and almost assuredly a young bird.
The codes we suggest are:
- N or 0 -
- No white spots showing, only a single, thin layer of bone covers the entire brain.
- T or 1 -
- Trace of pneumatization at the very back of the skull, usually appearing as an opaque, grayish crescent or a very small triangular area. Between 1 and 5 percent of the skull is pneumatized.
- L or 2 -
- Less than one-third pneumatized, but some is obvious. Generally the posterior part of the cranium has a triangular or circular area of small white dots, usually distinctly contrasting with the nonpneumatized area.
- H or 3 -
- Half the skull pneumatized, between one-third and two-thirds complete. Typically, most of the rear half is complete, as well as part of the front, extending back to the eyes. The front is usually difficult to see, because of dense, short feathers.
- G or 4 -
- Greater than two-thirds pneumatized, but at least a small area not complete, less than 95 percent complete.
- A or 5 -
- Almost complete pneumatization, between 95 percent and 99 percent complete. These birds show a tiny dull, pinkish area or windows.
- F or 6 -
- Fully complete pneumatization.
- U -
- Unknown, skull examined, but extent of pneumatization not determinable.
The best method for determining the sex of sexually monomorphic passerine birds during the breeding season is by the presence or absence of the cloacal protuberance in the male, and the brood patch, which primarily occurs in females. All North American landbirds develop at least one of these characteristics, at least partially, and most are reliably sexed by them during the late spring and summer months. Latin American birds are less well-known, but these guidelines should generally apply.
Cloacal ProtuberanceIn order to store sperm and to assist with copulation, external cloacal protuberances, or bulbs, are developed by male passerine birds during the breeding season. They usually begin to develop early in the spring and reach their peak size in 3-5 weeks. Depending on the species and the number of clutches attempted during the breeding season, cloacal protuberances will recede from mid to late summer.
Although the cloacal regions in females will sometimes swell slightly, or show a small protuberance, it rarely approaches the size of those in the males (the Wrentit appears to be an exception). If the swelling forms a gradual slope on the abdomen ending with the cloacal opening pointing towards the tail, then it is probably a female in breeding condition. When the female is most swollen in this area, she will usually also have a brood patch. A typical male protuberance essentially forms a right angle to the abdomen and is somewhat larger at the top than at the bottom.
To view the protuberance, blow the feathers apart in the region of the vent. The shape of the protuberance can be somewhat variable, and nonbreeding males may not always develop one. After a little experience with the shape of the cloacal region during the nesting season, biologists should have no problem separating breeding males from females.
We have categorized cloacal protuberances into four size categories (fig. 6): none (N or 0), small (S or 1), medium (M or 2), and large (L or 3). As one becomes familiar with the various extents of protuberances, one can make a judgment on the relative size.
Figure 6On the left, a cloacal protuberance at its peak in a male passerine. On the right a nonbreeding male (class = 0), a male beginning to be in breeding condition (class = S), and a male in full breeding condition (class = M). Class L would show a more prominent protuberance. Taken from Pyle and others (1987).
Brood PatchIncubation or brood patches are developed by incubating birds as a means of transferring as much body heat as possible to eggs or young in the nest. In most landbirds, females perform all or most of the incubating, and develop more substantial brood patches. The presence of a distinct brood patch can thus be used to reliably sex breeding females of almost all passerine species.
The development of the brood patch begins with the loss of the feathers of the abdomen, about 3-5 days before the first eggs are laid (Blake 1963). Shortly thereafter, the blood vessels of the region begin to increase in size, and the skin becomes thicker and filled with an opaque, whitish fluid. Figure 7a illustrates a full brood patch as viewed by blowing the feathers of the breast aside. A few days after the fledglings leave the nest, the swelling and blood vascularization will begin to subside. If a second clutch of eggs is laid, the process (except for defeathering) will be repeated. A new set of feathers on the abdomen are usually not grown until the prebasic molt, after completion of breeding. Between the end of nesting and the onset of molt, the skin of the abdomen will often appear grayish and wrinkled. Many young, and especially juvenile, passerine birds have little or no down or feathers on the belly; therefore the belly of some young look much like that of an adult who is just beginning to develop a brood patch, but the area will be quite smooth and usually a pink or dark red.
Figure 7Brood patches in different stages of development. Taken from Pyle and others (1987).
In most North American passerine birds, the male does not develop a brood patch in the breeding season. Slightly fewer feathers may be present on the abdomen than are found in the winter, but the breast retains a feathered appearance. In a few groups, in North America, notably the mimids, vireos, Myiarchis flycatchers, and a few other species (see Pyle and others 1987), the male will assist with incubation and develop an incomplete brood patch. This will include partial or complete feather loss and slight to moderate vascularization and swelling, which rarely or never approaches the extent of development typically found in females of the same species. Only in the Wrentit and the woodpeckers does the male develop a full brood patch.
We suggest recording brood patch in the order of its development as follows:
- N or 0 -
- No brood patch presentBreast more or less feathered. Nonfeathered areas of the breast and abdomen smooth without evident vascularization. In some species such as hummingbirds, and in most young birds, the breast is normally not feathered.
- S or 1 -
- Smooth skinA loss of breast and some abdomen feathers, but most of the area is still rather smooth and dark red.
- V or 2 -
- VascularizedAbdominal skin thickened with increased fluid and vascularization. This is the peak of incubation.
- W or 3 -
- WrinkledAbdomen skin thinning, wrinkly, and scaly.
- M or 4 -
- MoltingNew pin feathers are coming in on the abdomen. Nesting is usually completely over by this point.
The standard reference for measuring birds is Baldwin and others (1931), which outlines virtually every possible measurement. Although old, it is commonly listed as available in catalogs of used natural history books.
Size, as indicated by specific measurements such as wing, tail, or tarsus length, is often a useful characteristic for identifying, ageing, and especially, for sexing passerine birds in the hand. In almost all passerine species, the size of males of a given population will average larger than that of the females by about 5-10 percent. The extent to which the sexes overlap in size depends on both the species and the particular measurement being considered. Measurements also vary with age, but to a lesser extent than with sex. For example, juvenal primaries tend to be slightly (2-5 percent) shorter than adult primaries. Within each sex class, immature birds with juvenal primaries will have shorter wing lengths than adults. When coupled with weight and fat, size can also give a strong indication of the health of a bird.
When identifying, ageing, or sexing passerine birds it is important to use measuring techniques that are strictly standardized with those of published samples. In the following sections we recommend standardized methods for obtaining the measurements. All linear measurements should be recorded in millimeters (mm).
Wing LengthAlthough various methods of measuring wings are employed, we recommend that you measure the wing chord, because this is the length most frequently used and most widely published for North American birds, and is the most consistent between measurements. The wing chord is measured from the bend of the wing to the tip of the longest primary, across the natural arc of the primaries (fig. 8). While taking the wing measurement, avoid the tendency to flatten the natural curve of the wing, thus getting a measurement that is 2-5 percent longer than proper.
Figure 8Above, a good hold for measuring the wing chord, and below, the measurement of the wing chord and flattened wing. The wing chord is preferred in North America. Taken from Pyle and others (1987).
To measure the wing chord it is best to have a thin ruler with a perpendicular stop at zero. Insert the ruler under the wing, and place the bend of the wing (carpal joint or wrist) snugly against the stop. To avoid differences due to carpal compression, we recommend that the bend of the wing be pushed against the stop with no more pressure than the wing itself applies when the ruler is moved up to the wing. Once the wing is in place, make sure that the line between the carpal joint and the tip of the longest primary is parallel with the edge of the ruler, gently lower its tip to the ruler so that it touches it, and read the wing chord length (fig. 8).
When measuring the wing it is important to make sure that the longest primary is not broken, bent, or molting. Bent primary tips should be straightened. Older and more worn primaries will result in a shorter wing measurement and should be noted.
WeightBecause bird weight varies substantially with geographic population, condition of the individual, and season or period within the life cycle of each particular species, this measurement is not as useful for ageing, sexing, or identifying birds as is the wing chord. Weight, however, is an important indicator of the health of the bird, especially when coupled with wing length and fat content. It should always be recorded, when possible, to the nearest tenth of a gram.
Types of MoltRelatively little is known about the timing, sequence, and extent of molt in many species, especially in Latin America. A proper understanding of molt can be extremely helpful in the accurate ageing and sexing of passerine birds in the hand. With a few known exceptions, molting is confined to two periods within the annual life cycle of North American passerine birds, just before and just after the breeding season. Thus, most adult passerine birds display two plumages, the basic (winter) plumage and the alternate (summer or breeding) plumage. The molt that occurs just before the breeding season is called the prealternate molt; that occurring just after the breeding season is the prebasic molt. All North American passerine birds have a prebasic molt, and just over half (predominantly migratory species) have a prealternate molt.
The prebasic molt usually occurs from July to September on the breeding grounds and occurs in both recently fledged birds and adults that have completed nesting activities for the year. With one or two exceptions, the prebasic molt in adult passerine birds is complete (fig. 9; includes all body and flight feathers), whereas hatching year birds of most species typically replace the body feathers and some coverts, but not the primary coverts, and flight (wing and tail) feathers (except the central two tail feathers) during a partial first prebasic molt.
Figure 9An example of a wing during complete molt of an adult. Notice the worn primaries 7-9 and secondary 7. Taken from Pyle and others (1987).
As you blow apart the feathers on the various areas of the body, you can easily determine which feathers are molting by the presence of a cylindrical sheath around the base of the molting feather. When the feather is fully grown, this sheath is preened off and the feather ceases its traffic with the body and is thus fully grown.
Birds have three types of flight feathers: the rectrices, or tail feathers, and the outer (primary) and inner (secondary) wing feathers. The rectrices are numbered in pairs, beginning with the central ones (the decks) as #1, and proceeding outward in both directions usually to #5 or #6, depending upon the taxon. In some species the decks are sometimes molted by the young at the same time as their body feathers. The remaining rectrices molt in an ascendant sequence from #2 through #6.
The secondaries are long flight feathers attached to the skin at the ulna, the bone of forearm. These are numbered by all authors beginning at the bend of the wing and proceeding inward toward the body. This is the usual order of molt, except that the three innermost secondaries (tertials) molt like body feathers and may be molted by juveniles. They are also often molted concurrently with the longer secondaries.
The primaries are the long flight feathers attached to bones of the hand. These are numbered in most of the North American literature from the wrist-joint (bend of the wing) outward, which is the sequence that nearly all birds molt these feathers.
Pyle and others (1987) have provided a complete enumeration of the numbers of flight feathers of passerine birds in North America.
Recording MoltA basic system of recording molt in the flight feathers is to record presence or absence of molt in the primary feathers or the secondaries (except the innermost three). We suggest that the molt in the tail feathers not be recorded, except as a note. You should always check both wings, because birds often lose feathers accidentally (adventitious molt). Flight feather molt is S if symmetrical and normal, A if adventitious, and N or 0 if none.
More detailed recording of molt can be conducted using the British Trust for Ornithologys method (Ginn and Melville 1983).
Body molt can be recorded by a subjective determination of none (N or 0), trace (T or 1) (a few, perhaps adventitious molting feathers), light (L or 1) (involving more than one feather tract), medium (M or 2), or heavy (H or 3) molt.
Extent of Juvenal Plumage
We suggest that the extent of juvenal plumage be recorded, because it is a good indicator of the age of a young bird and the timing of breeding. Juvenal plumage can be coded in the following: N or 0 = no juvenal body plumage; L or 1 = less than half of juvenal plumage remains; H or 2 = more than half of the juvenal plumage remains, some first basic plumage is visible; F or 3 = full juvenal plumage, bird has not started first prebasic molt. For a more objective measure, the bander could estimate the percent of juvenal plumage.
Primary Feather Wear
Feather wear could be a useful indicator of age, because it seems likely that the juvenal generation of flight feathers may wear faster, and thus show more wear at any given time, than later, adult generations of feathers. Faster wear results from the rapid growth of juvenal feathers resulting in weaker feathers, and the protracted molt of adults. In some species during especially the early breeding season, adult flight feathers, molted after the previous breeding season, are much older than juvenal feathers and can help age birds.
Examine the outer four or five primaries to determine wear, and classify them according to the following scale: N or 0 = No wear, the feather edges are perfect, and the entire edge is light, including the tips; S or 1 = Slight wear, the feather edges are slightly worn with no fraying or nicks, and the edge is often light-colored, except at the tips; L or 2 = Light wear, the feathers are definitely worn, but with little fraying and few nicks; M or 3 = Moderate wear, considerable wear with definite fraying, and nicks and chips are obvious along the edges; H or 4 = Heavy wear, feathers very heavily worn and frayed, and the tips often worn completely off; and X or 5 = Excessive wear, feathers are extremely ragged and torn, the shafts are usually exposed well beyond the vane, and all the tips are usually completely worn or broken off (one wonders how well the bird can fly).
The amount of fat on a bird may indicate periods of stress, low availability of food, low fledging weight, and other conditions that give insight into the viability of an individual. Especially as birds prepare for migration, subcutaneous fat is accumulated and is visible beneath the skin as white, yellow, or light orange areas easily seen in contrast to the red muscular areas. The fat can be most easily seen on the abdomen and the furculum. The furcular or interclavicular region is the depression formed between the attachments of the pectoralis muscles to the furculum (the wish-bone) and coracoids, forming a V running toward the spinal cord and pectoral girdle, through which the neck protrudes. You can assign a fat class on the basis of how much fat you can find:
|N or 0||No fat, the region is concave||No fat|
|T or 1||Trace, deeply concave, scattered patches, less than 5 percent filled.||None, or a trace|
|L or 2||Thin Layer, less than a third filled.||Trace or thin layer|
|H or 3||One-Half filled in small patches||Small patches, not covering some areas.|
|F or 4||More than 2/3 Filled, level with clavicles||Covering pad, slightly mounded|
|B or 5||Slightly Bulging||Well mounded|
|G or 6||Bulging Greatly||Greatly distended mound|
|V or 7||Very large fat pads of furculum and abdomen meet|
We include a standard data form (fig. 10) that we encourage you to use. Fill in all the information, and print neatly in soft, black pencil. For codes not shown, and for exact definitions, see CWS and USFWS (1991). Right justify data in appropriate fields. Do not use ditto marks. If data are repeated on the next line, use a slanting line in the field from upper left to lower right, or a vertical line in the center of each column. If data are not collected, leave the column blank, or enter 9s for numerical data. If a band is lost or destroyed, indicate this in the code column and also in the species column. On any one sheet place only the records for one band size or the recaptured birds. When starting a new series of bands, or a new calendar year, always start a new banding sheet. The sheet is broken into the following categories:
- Heading material: State code, region code, band size (R for recaptures, entered on a separate sheet), page number (for each band size), and year of banding or capture.
- Recorder and banderPlace the initials of the recorder and bander here, and their full names at the bottom of the page (these are not entered into the data base).
- CodeThis column tells if it is a: new banding (N); recapture (R) (a bird previously banded); unbanded bird (U) (place 9s in the band number columns); destroyed band (D); lost band (L); or a changed band (C) (a band that replaced an old or worn bandmake a note of the old band number).
- Band numberThe full, right-aligned number of the first band on the first line. Thereafter, the final three digits of new bands only. Do not use dashes in this field to separate prefix; rather, right align all numbers. On recapture pages, the full band number should be entered each time.
- SpeciesAn abbreviation of the species name (e.g., Bl-cap Chick, for Black-capped Chickadee). The abbreviation is not entered into the data base, but is a check against the error-prone species codes below, such as Barn Swallow (BARS) and Bank Swallow (BANS).
- Species CodeThe four-letter code of species name (e.g., BCCH). The list of these for North America is in CWS and USFWS (1991). A Latin American version has not yet been prepared, but biologists can use the first two letters of the genus and the first two letters of the species names. This will suffice for many species.
- AgeThe single letter or numeric codes as indicated above.
- How agedUse the following codes: A, adult plumage; B, brood patch; C, cloacal protuberance; E, eye color; F, feather wear; H, hatching year (first winter) plumage; I, inside of mouth or any part of bill; J, juvenal plumage; M, molt; P, plumage in general; S, skull; T, tail length; W, wing length; or O, other (explain this code in the Notes section). Write the codes in their order of importance to your age determination.
- SexUse M for male, F for female, and U for unknown.
- How sexedUse the codes as in how aged.
- SkullRecord the code above that indicates the percent of skull pneumatized.
- Cloacal protuberanceUse the code described previously
- Brood patchUse the code described previously.
- FatUse the codes described previously.
- Body moltUse the codes described previously.
- Flight feather moltUse the codes described previously.
- Flight feather wearUse the codes described previously.
- Juvenal plumageRecord the extent of this plumage, using the codes described previously.
- Wing lengthRecord to the nearest millimeter.
- WeightRecord to the nearest tenth of a gram.
- StatusAmong the most common are: 300, normal and released; 301, color-banded; and 615, injured and released. The full list of status codes is in CWS and USFWS (1991).
- DateMonth, day, and year, all in numbers.
- Capture timeUsing the 24-hour clock, record to the nearest 10 minutes, e.g., 6:24 a.m. is 062, 4:48 p.m. is 165, etc.
- Station/locationRecord an abbreviation using four letters for the stations name and two numbers for the net location; a total of six columns used.
- NotesRecord any useful additional data, such as: sequence of color bands, if present; suspected ages or sexes of birds coded U; information on unusual wing lengths; or why an other code was used for how aged. If additional data are taken, such as an unusual age category, they should be placed in the Notes columns, in order to keep primary data consistent.
Figure 10An example of a form for recording data from captures.
Sources of Equipment1
Advertisements for supplies and good articles on capture techniques can be found in the publication North American Bird Bander. Persons doing mist netting or banding should join their regional Association and receive this, the joint publication of the Western Bird Banding Association (BBA), 1158 Beechwood St., Camarillo, CA 93010 (Colorado and west); Eastern BBA, R.D. #2, Box 436A, Hellertown, PA 18055 (Appalachians and east); or the Inland BBA, 81 Woodshire Drive, Ottawa, IA 52501.
1 The use of trade or firm names in this publication is for reader information and does not imply endorsement by the U.S. Department of Agriculture of any product or service.
Nets can be purchased in the United States at the following:
Association of Field Ornithologists, c/o Manomet Bird Observatory, Box 936, Manomet, MA 02345 [telephone (508) 224-6521]. A wide assortment of nets.
Avinet, P.O. Box 1103, Dryden, NY 13053 [telephone and FAX: (607) 844-3277]. They have a wide selection of nets, banding tools, scales, poles, color bands, and other material.
Eastern Bird-Banding Association, Gale W. Smith, R.D. #2, Box 131, Kempton, PA 19529. An assortment of nets.
The only source of split-ring plastic color bands for landbirds that we have found is A.C. Hughes, Ltd., 1 High Street, Hampton Hill, Middlesex TW12 1NA, England. Avinet (see above) carries a limited supply of Hughes bands.
The best bands for most species are the Plastic Split Rings in solid colors. We have found their five most visible and separable colors are Red, Yellow, Light Blue, Dark Blue, and Orange. If more colors are needed, some investigators have found White reasonably separable from the standard aluminum band, and the Black and the Dark Green separable from the Dark Blue. Hughes sizes (and their Fish and Wildlife Service approximate equivalents) are: XF (0), XCS (1), XCL (1B), XB (1A), and X3 (2).
Optical Device for Skulling
An excellent one is OptiVisor, a binocular magnifier available in 2.5, 2.75 and 3.5 powers. Available from the manufacturer Donegan Optical Company Incorporated, P.O. Box 14308, Lenexa, Kansas 66285-4308, or call them at (913) 492-2500 for a distributor near you.
Rigid tempered steel rules with a stop at the end are very good for measuring wings. Sizes are 15 cm, 30 cm, and 60 cm. Available from Chris N. Rose, 98 Lopez Rd., Cedar Grove, NJ 07009.
The best have holes in jaws to fit standard U.S. band sizes, with a split pin on top for even band opening. Three pliers are available: one will open all of band sizes 0, 1, 1B, and 1A; another for sizes 2 and 3; and one for sizes 3B, 3A, and 4. These are available from Roger N. MacDonald, 850 Main St., Lynnfield, MA 01940, (617) 334-3448.
Scales for Weighing
Electronic scales are widely available for under $300, and Pesola scales and a spring balance field scale are available through Avinet (see above). A good general purpose one has a capacity of 300 g and a readability of 0.1 g. The Ohaus C-Series costs under $200 and Acculab has one under $150. With a capacity for most birds, Acculab has a pocket balance with 80 g capacity for under $100. These are available from many scientific supply houses, such as Markson, P.O. Box 3944, Houston, Texas 77253 (800-528-5114).
Bags for Holding Birds
Washable bags can be made, or cotton mailing bags can be purchased. An ideal size for most small birds is 6 by 9 inches, or somewhat larger. U.S. Government agencies can purchase excellent cotton mailing bags from the General Services Administration.
Bird Banding Laboratory and Office
All capture work must be done under very strict regulations and permits. Permit applications in the United States can be obtained from the Bird Banding Laboratory, U.S. Fish and Wildlife Service, Laurel, Maryland 20708. In Canada, the address is Canadian Bird Banding Office, Canadian Wildlife Service, Environment Canada, Ottawa, Ontario K1A 0H3. Special permits are also needed from most states and provinces, and the above offices can supply information on them. Many Latin American countries also require permits.
The Bird Banding Laboratory and Office provide excellent support for all activities relating to capture, and permittees receive bands at no cost. However, they have limited resources for supporting banding work and cannot honor all requests for permits. Applicants for permits must show evidence of qualifications and must have a well-justified need to band. Permittees are expected to provide accurate and timely reports of birds banded.