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Monitoring Survival Rates of Landbirds
at Varying Spatial Scales: an Application of the MAPS Program Daniel K. Rosenberg1,3, David F.
DeSante1, and James E. Hines2.
| ABSTRACT—Survivorship is a
primary demographic parameter affecting population dynamics, and thus trends in species
abundance. The Monitoring Avian Productivity and Survivorship (MAPS) program is a
cooperative effort designed to monitor landbird demographic parameters. A principle goal
of MAPS is to estimate annual survivorship and determine spatial patterns and temporal
trends in these rates. We tested hypotheses of spatial patterns in survival rates among a
collection of neighboring sampling sites, such as within national forests, among
biogeographic provinces, and between breeding populations that winter in either Central or
South America, and compared these geographic-specific models to a model of a common
survival rate among all sampling sites. We used data collected during 1992-1995 from
Swainson's Thrush (Catharus ustulatus) populations in the western region of
the United States. We evaluated the ability to detect spatial and temporal patterns of
survivorship with simulated data. We found weak evidence of spatial differences in
survival rates at the local scale of "location", which typically contained 3
mist-netting stations. There was little evidence of differences in survival rates among
biogeographic provinces or between populations that winter in either Central or South
America. When data were pooled for a regional estimate of survivorship, the percent
relative bias due to pooling "locations" was <1%. With the pooled data, we
estimated a 44% annual regional survival rate; this low survival rate was likely due to
the presence of transients in the population. Using simulated data, we found that power to
detect spatial differences increased considerably with number of years and spatial scale,
the latter reflecting larger sample size. Detection of trends at smaller spatial scales
required >12 years of monitoring. Detection of spatial patterns and temporal trends in
survival rates from local to regional scales will provide important information for
management and future research directed towards conservation of landbirds.
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1The Institute for Bird Populations
P.O. Box 1346
Point Reyes Station, CA 94956.
2 National Biological Service
Patuxent Environmental Science Center
Laurel, MD 20811
3 Present Address:
Oregon Cooperative Fish and Wildlife Research Unit
Department of Fisheries and Wildlife
Oregon State Unversity
Corvallis, OR 97331
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