Identifying Causes of Population Change in Migratory Birds

Recent progress has been made in analyzing spatio-temporal MAPS demographic patterns relative to other continental-scale monitoring datasets.

An interim project report summarizes MAPS productivity indices, adult apparent survival-rate estimates, and North American Breeding Bird Survey (BBS) population trend estimates for 183 landbird species at the continental scale over the period 1992-2003.  MAPS vital rate indices and estimates and BBS trend estimates are also provided for 39 target species at smaller spatial scales (Bird Conservation Regions and BBS Physiographic Strata).  We summarize spatial and temporal patterns in MAPS data and report results of exploratory analyses linking vital rates and population trends.  A manuscript reporting these findings is in preparation for a peer-reviewed journal.

J. F. Saracco, D. F. DeSante, D. R. Kaschube. Assessing landbird monitoring programs and demographic causes of population trends (in prep.)

Population trend data from the North American Breeding Bird Survey (BBS) have been used to identify conservation priorities and to justify major conservation initiatives such as Partners in Flight (PIF). Yet the BBS has been criticized for relying on abundance indices to estimate trends. Here we compare 1992-2003 BBS trend estimates for 36 wood-warbler (Parulidae) taxa to trend estimates from another broad-scale monitoring program, the Monitoring Avian Productivity and Survivorship (MAPS) program. Estimates were strongly correlated, suggesting that each program can provide accurate trend information. We then asked whether landbird population trends have improved since major PIF efforts were established. Comparison of 1981-1992 BBS trend estimates to 1992-2003 trend estimates suggest that trends have gotten worse (more negative), rather than better. We argue that management based on the identification of deficient vital rates can provide an effective solution for improving landbird population trends. Here we illustrate two approaches using 1992-2003 MAPS and BBS data for orange-crowned warbler (Vermivora celata). The first approach modeled adult apparent survival rates (f) and population growth rates (λ) as functions of the MAPS reproductive index (ratio of young to adult birds captured). The second compared MAPS survival-rate estimates and reproductive indices for 9 BBS physiographic strata to BBS trend estimates in those strata. Both approaches suggested the importance of survival in effecting population declines. Once deficient vital rates are identified, management strategies aimed at reversing declines can be determined by modeling deficient vital rates as functions of habitat variables.

[BACK]

This page was last updated 12/29/2006