General Technical Report
PSW-GTR-144-Web

Selecting Monitoring Methods and Location of Monitoring Stations

Before beginning work, careful attention should be given to selecting the appropriate method for the questions being asked, and great care should be given to selecting locations of monitoring stations to best answer these questions.

Selection of Methods

The standardized set of methodologies described below should be followed closely to ensure compatibility with those of other monitoring stations. These methodologies are integrated and hierarchic, so as to allow a region’s sampling schemes to complement other programs and to allow comparisons between monitoring stations in a region, and between regions.

  Methods recommended should be employed for a minimum of three years, and preferably longer. However, depending on individual objectives, some results may be obtainable in a year or two.

What Will the Data from This Program Provide?

These data will be used at two geographic scales. At the level of the managed forest, for instance a large National Forest District, they will provide a local assessment of the status and trends of landbirds. The scheme below samples the landscape as a whole within the unit and will permit statements such as: “Scarlet Tanagers have significantly increased on the sampled units in the forest,” “Hermit Thrushes have had high mortality during migration or the winter in the past two years,” or “15 of 20 neotropical migrants have increased over the past 3 years.” Such a local scheme will permit some investigation of patterns of population change (e.g., “are declining trends more prevalent in units of the northern half of the forest?”, “do increasing trends appear to be associated with certain forestry practices?”). Their primary purpose, however, is to estimate the status and trends of the population. Assessment of the cause of population change, or associations with environmental factors such as cutting practices, are more efficiently studied by other research programs with more appropriate techniques.

  At the larger scale, perhaps a Forest Service Region, a state, or a province, the program will permit evaluation of geographic patterns of various attributes of landbirds. It is important to realize that the program cannot evaluate the population status of birds of the entire geographic area, whether regional, state, federal, or continental. If, for example, samples are only from forested environments, only statements about birds using forested lands can be made. Additionally, because sites are chosen by the unit, and are not a random sample of all available units or sites, the program can investigate only the patterns of population change, rather than the population’s overall status. Questions this approach can answer, for example, are: “are population increases or reproductive failures in a group of species more prevalent in some regions or states?”; “what is the association between forest management and population status of a group of species?”; “do some forest types have more neotropical migrants than others?”; or “are populations increasing in some forest types, but not in others?”

Coverage

While it would be best to have complete coverage of any state, province, or region, we do believe that it is acceptable and inevitable that gaps will exist. These gaps will occur within habitat types, forests, states, provinces, or regions. At a minimum, we hope to have several units involved in each state, province, or region. We strongly urge that each unit have both population and demographic methods in operation, and cover anything from a few hundred to several thousand acres. Further, we suggest that sampling within a unit should be stratified by at least general habitat type, such as “mixed coniferous forests,” “tropical thorn forest,” or “coastal chaparral.” Samples in an analysis, in general, should not be pooled across habitat types. The data from these units would be searched for large-scale patterns, e.g., species showing consistent declines over the entire region or within a given habitat type. Results from these investigations will identify patterns that need further research or greater intensity of monitoring to determine their causes. The overall program could be considered a large-scale hypothesis-generating mechanism.

Priorities

Methodologies are compared in table 1. At a minimum we recommend that the following programs of demographic and population monitoring be implemented in each unit, in the following order. Although this handbook describes three censusing methods, the point count method has been adopted as the recommended standard, and its implementation is suggested below. Each recommended method is in segments of 10 person-days, other than the first which takes one person-day. For example, if funding is available for 21 person-days of field work, then only Priorities I through III (outlined below) would be implemented. These estimates of time do not include set-up or training. These will vary depending upon qualifications of personnel. The minimum numbers of counts or netting sites, noted below, are derived from our experiences with many such population monitoring programs. We believe they are useful, but not restrictive, minima for a unit’s effort.

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Table 1—Census and demographic monitoring methods

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	Census			Demographic
Variables and characters	Point count	Spot map	Area search	Mist nets	Nest search
Variables measured
Index to abundance	yes	yes	yes	yes	partly
Density	no	yes	no	no	partly
Survivorship (adult)	no	no	no	yes	no
Survivorship (juvenile)	no	no	no	yes	partly
Productivity	no	no	no	yes	yes
Recruitment	no	no	no	yes	no
Habitat relations	yes	yes	yes	little	partly
Clutch size	no	no	no	no	yes
Predation/parasitism	no	no	no	no	yes
Individuals identified	no	no	no	yes	yes
Breeding status known	no	yes	no	partly	yes
General characters
Habitat types measured	all	some	most	some	few
Habitat specificity	good	good	good	fair	good
Rare species measured	many	few	many	some	few
Canopy species measured	all	all	all	some	few
Area sampled known	partly	yes	yes	partly	yes
Size of area sampled	moderate	small	small	large	small
Training necessary	much	much	moderate	much	much
Observer error potential	high	high	moderate	moderate	moderate
Use in non-breeding	yes	no	yes	yes	no
Cost per data point	low	high	low	high	very high
Applicable scale	broad	local	broad	broad	local

  Priority I. Breeding Bird Survey—If the unit is in North America and has an unsurveyed Fish and Wildlife Service Breeding Bird Survey route within or near it, we recommend that the standard survey be conducted. This involves 50 3-minute point counts along roads at 0.5-mile (1-km) intervals. The effort takes one person-day at the height of the breeding season, usually in early June. The surveyor must know all of the vocalizations of species likely to be encountered. This Survey will help detect regional trends in many species in the unit, or its vicinity.

  Priority II. On-Road Point Counts—As a second priority, we recommend that the unit put in point-counting stations in multiples of about 250 stations to monitor overall population changes and responses to habitats. We suggest that the stations be in habitats representative of the unit, stratified by these major habitats, systematically placed, and placed primarily along secondary roads. This level of effort will require about 10 person-days during the early breeding season, usually in May or June. It is based on the assumption that in the 10-day period, an average of about 25 stations can be censused in each day. While we acknowledge the fact that an on-road monitoring program is not without bias, the benefits are considered by most workers to outweigh the disadvantages, and are at least partly offset by Priority IV, below.

  Priority III. Demographic Monitoring—We recommend that the unit establish at least one site to measure demographic parameters. Either constant-effort mist netting or nest searches (both, if possible) should be conducted on usually about six plots within each unit. These monitoring stations will estimate demographic variables that influence the density estimates.

  Constant-Effort Mist-Netting Sites—Operating mist nets through the breeding season, at most North American stations, will require about 10 person-days per site, beginning about June and continuing through the end of August. In Latin America, the season would be longer. The program will provide information on productivity, survivorship, and movement of many species. Mist netting involves capturing birds, banding them, and taking data on age, sex, breeding status, molt, and survivorship. At a minimum each monitoring station should operate 8-12 nets at least once every 10 days throughout the breeding season. It has become well established that results from constant-effort mist netting provide excellent indexes of productivity and recruitment for a variety of species (e.g., DeSante and Geupel 1987, Peach and others 1990, Peach 1992). It is the only method that estimates survivorship and recruitment using mark and recapture. Its major weakness is that the recruitment data are not habitat specific, especially late in the summer. The survivorship data are excellent, and all data are most habitat specific for adults, especially early in the breeding season. As the season progresses, influx of peripheral birds and young from other areas dilutes this specificity.

  Nest Searching Sites—Nest searches involve intensively finding nests in a plot. Typically, one plot can be done in about 20-40 person-days, beginning about May and continuing to about August. Nest searching involves finding nests, monitoring their outcome, and measuring associated vegetation. A study plot needs to be visited at least once every four days to find and check nests. Nest searches provide direct measures of reproductive success (rather than an index) and can provide direct data on influences of habitat on reproductive success and the incidence of nest parasitism. Nest searching, however, is quite labor intensive and is applicable to fewer species than mist netting.

  A drawback to both demographic methods is that they will assay the population health of only certain species in an area. As a general rule of thumb, usually about 10 species at any one station will be monitored. However, when data from several stations are combined over a larger geographical area, meaningful insights may be gained on many species.

  In addition, within each demographic plot, at least 9-16 intensive point count censuses should be conducted at least twice during the peak of the breeding season. Other census methods (i.e., spot mapping, area search) may also be employed, depending on objectives, size of study area, and availability of personnel. Vegetation measures should also be made at each census point and within each demographic plot.

  Priority IV. Off-Road Point Counts—As a fourth priority, we recommend that the unit conduct point counts in segments of approximately 100 points off-roads in habitats not covered by the on-road point counts. Each segment of 100 points will require up to 10 person-days during the same period as on-road counts, and assumes about 10 stations per day are covered along trails or cross-country.

  Priority V. Additional Work—When resources are available, we recommend that the unit add programs, in increments of 10 person-days, of the three programs (II-IV) above. We do encourage additions of programs in the order they are recommended. However, local conditions, variety of habitat types, length of sampling season, areas of management concern, and consultation with biostatisticians will modify the order and magnitude of additional work in each unit. Additionally, at some point a unit will be best served collecting information other than that outlined above.

Selection of a Station Location

A monitoring station should be located in representative habitat for a given region, or in a habitat of concern. A station may have a variety of habitat types, and some will have a higher density of birds than others. Because the derived population and demographic parameters are likely to be highly sensitive to successional changes in the habitats sampled, stations should not be placed in very young habitats. However, young habitats are acceptable if they are held in a lower successional stage by active management.

  If the census methods involve extensive point counts, the points can be spread out along a road or trail network, over a fairly large area of the region. This makes for a robust data set, because each point is at a location somewhat representative of the habitats in the region. In spot mapping and nest searches, a plot is usually established in a single habitat type, and is usually square or rectangular. Plots in heterogeneous habitat are often not as useful because they are more difficult to generalize about.

  For constant-effort mist netting, we suggest the capture array be placed where a high rate of capture can be achieved. By contrast, extensive census points and the nest search plot should be placed in the representative habitats of the region.

Permanent Stations

While the need for broad-scale monitoring is of vital importance, in-depth studies in small, protected areas, such as natural areas, nature reserves, and parks, can contribute greatly to our knowledge of landbird populations. In-depth studies of bird life histories (normally using individually color-banded birds) can provide important insights into vulnerability and management of species. Other biological studies concurrently conducted at the station can add greatly to our knowledge of the factors affecting local landbird populations. Monitoring stations with active field programs or living quarters for biologists are ideal for intensive programs in remote areas and can often attract volunteers.

  Obtaining institutional sponsorship of permanent stations can provide long-term commitment over many years. A monitoring program with such a commitment will continue despite turnover in personnel and can provide some stability in funding. Furthermore, by using local volunteers to collect data in such a program, a community outreach and education program can be established. Bird observatories and some university field stations in North and Latin America have been conducting programs similar to this for many years.