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ABSTRACT Avian irruptions are facultative, often periodic, migrations of thousands of birds outside of their resident range. Irruptive movements produce regional anomalies of abundance that oscillate over time, forming ecological dipoles (geographically disjunct regions of low and high abundance) at continental scales. Potential drivers of irruptions include climate and food variability, but these relationships are rarely tested over broad geographic scales. We used community science data on winter bird abundance (1989–2021) to identify spatiotemporal patterns of irruption for nine boreal birds across the United States and Canada and compared them to time series of winter climate and annual tree seed production. We hypothesized that, during irruption, bird abundance would decrease in regions experiencing colder winter climates (climate variability hypothesis) or low seed production resulting from the boom‐and‐bust of widespread mast‐seeding patterns (resource variability hypothesis). Across all species, we detected latitudinal or longitudinal irruption modes, or both, demonstrating north–south and east–west migration dynamics across the northern United States and southern Canada. Seven of nine species displayed associations consistent with the climate variability hypothesis and six with the resource variability hypothesis. While irruption dynamics are likely entrained by multiple environmental drivers, future climate change could alter the spatial and temporal characteristics of avian irruption.
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This content will become publicly available on July 1, 2026
The influence of geographic ranges, climatic niches and temperature fluctuations on population variability
The existence of patterns in population dynamics across species geographic ranges and climatic niches is a pervasive idea in ecology. Population variability (i.e. temporal variability in population density) should hypothetically increase near range edges or niche limits because of less suitable environments in these areas, but the occurrence of such patterns remains largely unexplored. Further, fluctuations in temperature could pose demographic constraints on populations and also influence their variability. We used Breeding Bird Survey data to show that the population variability of 97 resident North American birds consistently increases towards their niche limits and in areas with more variable temperatures, but not towards their geographic range edges. However, our model has limited explanatory power, and phylogenetic history and species traits could not explain these results. These findings suggest that other factors, such as biotic interactions and resource availability, might be more important drivers of population variability in resident North American birds.
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- PAR ID:
- 10630335
- Publisher / Repository:
- The Royal Society
- Date Published:
- Journal Name:
- Proceedings of the Royal Society B: Biological Sciences
- Volume:
- 292
- Issue:
- 2051
- ISSN:
- 1471-2954
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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