Abstract
Many bird species do not make their own nests; therefore, selection of existing sites that provide adequate microclimates is critical. This is particularly true for owls in north temperate climates that often nest early in the year when inclement weather is common. Spotted owls use three main types of nest structures, each of which are structurally distinct and may provide varying levels of protection to the eggs or young. We tested the hypothesis that spotted owl nest configuration influences nest microclimate using both experimental and observational data. We used a wind tunnel to estimate the convective heat transfer coefficient (hc) of eggs in 25 potential nest configurations that mimicked 2 nest types (top-cavity and platform nests), at 3 different wind speeds. We then used the estimates of hc in a biophysical heat transfer model to estimate how long it would take unattended eggs to cool from incubation temperature (∼36°C) to physiological zero temperature (PZT; ∼26°C) under natural environmental conditions. Our results indicated that the structural configuration of nests influences the cooling time of the eggs inside those nests, and hence, influences the nest microclimate. Estimates of time to PZT ranged from 10.6 minutes to 33.3 minutes. Nest configurations that were most similar to platform nests always had the fastest egg cooling times, suggesting that platform nests were the least protective of those nests we tested. Our field data coupled with our experimental results suggested that nest choice is important for the reproductive success of owls during years of inclement weather or in regions characterized by inclement weather during the nesting season.
Highlights
The ability of many bird species to build or modify their nests in response to environmental stressors, such as climate, is an important behavior linked to nestling survival and reproductive success
Patterns of Nest Type Use Our results demonstrated that different spotted owl nest structures influence the cooling time of unattended eggs and nest microclimate
We found that platform nests (NDD ratio = 0) consistently had the shortest times to physiological zero temperature (PZT), indicating that these configurations provided the least amount of protection against convective heat loss
Summary
The ability of many bird species to build or modify their nests in response to environmental stressors, such as climate, is an important behavior linked to nestling survival and reproductive success. Behavioral responses to environmental stressors such as ambient temperature and wind generally include varying nest placement and modifying nest construction [2,3,4,5,6,7,8,9]. Burton [13] elucidated a relationship between nest entrance orientation and latitude among ground-nesting passerines He found a strong trend for preference of north-facing nests at lower latitudes, east-facing nests at mid-latitudes and southfacing nests at upper latitudes and attributed this to the variation in ambient temperatures across this gradient
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