Changes to weather patterns under a warming climate are complex: while warmer temperatures are expected virtually worldwide, decreased mean precipitation is expected at mid-latitudes. Migratory birds depend on broad-scale weather patterns to inform timing of movements, but may be more susceptible to local weather patterns during sedentary periods. We constructed Bayesian integrated population models (IPMs) to assess whether continental or local weather effects best explained population dynamics in an environmentally sensitive aerial insectivorous bird, the tree swallow (Tachycineta bicolor), along a transcontinental gradient from British Columbia to Saskatchewan to New York, and tested whether population dynamics were synchronous among sites. Little consistency existed among sites in the demographic rates most affecting population growth rate or in correlations among rates. Juvenile apparent survival at all sites was stable over time and greatest in New York, whereas adult apparent survival was more variable among years and sites, and greatest in British Columbia and Saskatchewan. Fledging success was greatest in Saskatchewan. Local weather conditions explained significant variation in adult survival in Saskatchewan and fledging success in New York, corroborating the hypothesis that local more than continental weather drives the population dynamics of this species and, therefore, demographic synchrony measured at three sites was limited. Nonetheless, multi-population IPMs can be a powerful tool for identifying correlated population trajectories caused by synchronous demographic rates, and can pinpoint the scale at which environmental drivers are responsible for changes. We caution against applying uniform conservation actions for populations where synchrony does not occur or is not fully understood.
Bibliographical noteFunding Information:
We thank the dozens of volunteers and student employees who contributed to the data in this paper, especially P.-P. Bitton, E. O’Brien, C. Coady, S. Unger and L. Berzins at Prince George, C. Fehr, T. Diamond, D. Shutler, P. Leighton, M. Fast, L. Bartolotti and V. Harriman at St. Denis, and N. Hamm, P. Wrege, S. Orzechowski and T. Pegan at Ithaca. Work at Ithaca was supported by NSF Grants IBN-9207231, IBN-013437, DEB-0717021, DEB 1242573, IOS-0744753, OISE-0730180 and Hatch Grant 183-428 to DWW. Work at Prince George and St. Denis was supported through NSERC grants to RDD and RGC, respectively. We thank N. Michel for assistance in analyses and preparation of this manuscript. We thank our respective universities for their support of this research. Finally, we thank D. Koons, R. Robinson and an anonymous reviewer for their helpful comments to previous versions of this paper.
© 2017, Springer-Verlag Berlin Heidelberg.
- Climate change
- Horvitz–Thompson estimator
- Long-distance migrant bird