Abstract
Simple SummaryEnvironmental changes such as climate change have affected wildlife species behavior and geographic ranges globally. We analyzed nesting data of western bluebirds to determine whether the link between geographic range shifts of a western bluebird population in New Mexico, USA is due to individual adaptations or changes occurring at a larger scale. We looked at location data of marked and recaptured nestlings and adults that nested within our study area. We found that individual choices have no impact on the geographic range shift being observed in this population, suggesting that population-level processes, such as emigration and immigration, may be the main cause of these shifts.Geographic ranges of plants and animals are shifting due to environmental change. While some species are shifting towards the poles and upslope in elevation, the processes leading to these patterns are not well known. We analyzed 22 years of western bluebird (Sialia mexicana) data from a large nest box network in northern New Mexico at elevations between 1860 m and 2750 m. This population has shifted to higher elevations over time, but whether this is due to changes in nesting behavior and preference for higher elevation within the population or driven by immigration is unclear. We banded adults and nestlings from nest boxes and examined nesting location and elevation for individual birds captured two or more times. Most recaptured birds nested at the same nest boxes in subsequent years, and the number of birds that moved upslope did not significantly differ from the number that moved downslope. Fledglings moved greater distances and elevations than adults, but these movements were not upslope specific. Female fledglings showed greater changes in elevation and distance compared to male fledglings, but again, movements were not consistently upslope. The upslope shift in this population may be due to birds immigrating into the population and not from changes in individual nesting behavior.
Highlights
Populations of plants and animals are responding to anthropogenic environmental change worldwide [1,2,3,4]
Climate change and changes to habitats mean that species must adapt to new environmental conditions [5] or shift their geographic ranges to match their preferred climate regimes
Each bird was plotted according to the year in which it was initially captured and subsequently recaptured with the corresponding elevation of the nest box in which it nested for that year (Figure 1a)
Summary
Populations of plants and animals are responding to anthropogenic environmental change worldwide [1,2,3,4]. Climate change and changes to habitats mean that species must adapt to new environmental conditions [5] or shift their geographic ranges to match their preferred climate regimes (i.e., niche conservatism; [6]). If a species can neither adapt nor shift its distribution because of geographic constraints, it may be vulnerable to local extinction [6,8]. This may be especially true for species that are range-restricted and for species that may already be pushed to the limits of their climatic or geographic niche; for example, species on mountaintops [9,10]. The effects of climate change and climate niches on geographic range shifts of populations and communities are still unpredictable, but general movement upslope and towards the poles has been observed in many species [12]
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