United States Department of Agriculture
Pacific Southwest Research Station
General Technical Report
|Index to abundance||yes||yes||yes||yes||partly|
|Breeding status known||no||yes||no||partly||yes|
|Habitat types measured||all||some||most||some||few|
|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|
|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|
Priority I. Breeding Bird SurveyIf 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 CountsAs 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 MonitoringWe 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 SitesOperating 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 SitesNest 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 CountsAs 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 WorkWhen 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.
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.
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.