There is widespread evidence that species distributions are shifting in response to climate change. Warming temperatures and climate niche constraints are hypothesized drivers of northward shifts in temperate migratory bird breeding distributions, but heterogeneity in the direction of distribution shifts suggests that the climate niche hypothesis does not explain all changes in distributions. We propose that: 1) changes in migration costs and benefits related to dampened seasonal differences between breeding and winter areas, 2) sensitivity to supplemental cues that affect duration of migration and onset of reproduction, 3) a latitudinal mismatch-driven fitness gradient, or a combination of these drivers may explain southward distribution shifts. We examined latitudinal shifts in breeding distribution centroids for 73 species of migratory birds from 1994 to 2017 across eastern, central and western regions of North America using Breeding Bird Survey data and tested if life history characteristics related to the above hypotheses and population status were associated with shift patterns. We found that 44% of regional centroid shifts were southward, 55% were northward, and several species shifted in different directions in different regions. Migratory strategy and protandry predicted breeding distribution centroid shifts, although they tended to be more predictive of northward shifts than southward shifts. There was evidence that supplemental cues explained some southward shifts because herbivorous birds tended to shift southward compared to insectivores, or raptors that shifted northward. Shifts in centroids were not explained by trends in abundance, suggesting that centroid shifts were not attributable to population declines or increases at distribution margins. Our results show the prevalence of heterogeneous breeding distribution shifts, including often overlooked southward shifts, and suggest that more work is needed to develop alternative hypotheses that would explain southward shifts in distributions.
This is the peer reviewed version of the following article:
McCaslin, H.M. & Heath, J.A. (2020 March). Patterns and Mechanisms of Heterogeneous Breeding Distribution Shifts of North American Migratory Birds. Journal of Avian Biology, 51(3), e02237.
which has been published in final form at https://doi.org/10.1093/auk/ukaa051. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.
McCaslin, Hanna M. and Heath, Julie A.. (2020). "Patterns and Mechanisms of Heterogeneous Breeding Distribution Shifts of North American Migratory Birds". Journal of Avian Biology, 51(3), e02237, . https://doi.org/10.1111/jav.02237