Treesearch

Accurate and precise estimates of numbers of animals are vitally needed both to assess population status and to evaluate management decisions. Various methods exist for counting birds, but most of those used with territorial landbirds yield only indices, not true estimates of population size. The need for valid density estimates has spawned a number of models for estimating p, the ratio of birds detected to those present. Wildlife biologists can be assisted in evaluating these methods by appreciating several subtleties of p: (1) p depends upon the duration of the count, (2) p has two...

Point counts are a standard sampling procedure for many bird species, but lingering concerns still exist about the quality of information produced from the method. It is well known that variation in observer ability and environmental conditions can influence the detection probability of birds in point counts, but many biologists have been reluctant to abandon point counts in favor of more intensive approaches to counting. However, over the past few years a variety of statistical and methodological developments have begun to provide practical ways of overcoming some of the problems with...

Summary of bird survey information is a critical component of conservation activities, but often our summaries rely on statistical methods that do not accommodate the limitations of the information. Prioritization of species requires ranking and analysis of species by magnitude of population trend, but often magnitude of trend is a misleading measure of actual decline when trend is poorly estimated. Aggregation of population information among regions is also complicated by varying quality of estimates among regions. Hierarchical models provide a reasonable means of accommodating concerns...

We investigated increasing the number of Breeding Bird Survey (BBS) routes and reducing potential bias as ways to increase the number of species adequately monitored by the BBS in the Pacific Northwest. Estimates of place-to-place variance in trends were used to assess the effects of increasing the number of additional BBS routes. Increasing the number of BBS routes from the current number (149) to 210 would increase the number of adequately covered species, using a recently proposed standard, from 42 at present to 60. If potential bias was reduced from its estimated current value (0.008)...

A conviction has developed during the past few years within the avian conservation community that estimates of total population size are needed for many species, especially ones that warrant conservation action. For example, the recently completed monitoring plans for North American shorebirds and landbirds establish estimating population size as a major objective. Obtaining these estimates rigorously, however, is difficult. Rosenberg and Blancher (this volume) describe one approach that generates point estimates based on several assumptions. Here, I describe an alternate approach which...

This paper presents preliminary results from the first year of a two-year study designed to evaluate bias in a typical songbird survey by examining differences in detection ratios among species, cover types, and time of the season. Detection ratios, calculated as number of individuals detected during a 15-25 minute fixed-width transect survey divided by the number of individuals shown to be present through intensive nest searching and territory mapping, were obtained for riparian songbirds on 22, 1.5-ha plots in southeastern Oregon. During intensive territory mapping and nest finding,...

Available information on the ecology of neotropical migrants during the winter season and especially during migration is far behind the existing knowledge of birds during the breeding season. This paper presents a stopover ecology case study. We document the occurrence of species, outline the prevailing weather patterns during spring and fall migration seasons, and present an analysis of the landscape and land use indices from central Veracruz, México, to better understand the relationship between birds and some of the variables that model their migration strategies. The central Veracruz...

The Gulf Coast Bird Observatory (GCBO) and the Southeastern Working Group of Partners in Flight have developed a protocol to monitor landbirds with volunteer observers performing avian censuses in the field. Field observations are compiled within a powerful internet database, and recording and summary capability is maintained by the GCBO. More than 100 observers have supplied data from sites primarily in the southeastern United States. Results of three case studies are presented, illustrating the application of migration monitoring data to land conservation, community education, and...

Several aspects of a developing program to monitor shorebirds in the western hemisphere are pertinent to migration monitoring of landbirds. Goals of the Program for Regional and International Shorebird Monitoring (PRISM) include estimating population size and population trends of 74 species, sub-species and distinct populations of North American shorebirds, monitoring shorebird use at stopover locations, and assisting local managers in meeting management goals. Migration monitoring, one of three components of PRISM, works in concert with breeding and wintering surveys to achieve these...

Raptors are secretive, area-sensitive predators whose populations can be logistically difficult and financially prohibitive to monitor. Many North American populations of raptors are migratory however, and on migration raptors are frequently counted at traditional migration watchsites. Experiences at Hawk Mountain Sanctuary (HMS) and elsewhere suggest that long-term migration counts can be used to monitor regional populations of raptors. Hawkwatchers have collected count data on standardized Hawk Migration of North America (HMANA) Daily Report Forms since the mid- 1970s. In 1998 HMS,...