Effects of cavity orientation on nesting success inferred from long-term monitoring of the endangered red-cockaded woodpecker

Abstract

Animals that create structures often display non-random patterns in the direction of their constructions. This tendency of oriented construction is widely presumed to be an adaptive trait of the constructor’s extended phenotype, but there is little empirical support for this hypothesis. Particularly, for cavity nesting-birds there is a lack of studies examining this issue. In this study of a primary cavity excavator, the endangered red-cockaded woodpecker (Dryobates borealis), we show that cavity entrances exhibited a strong westward bias in all 11 of the populations examined throughout the geographic range of the species in the southeastern United States. This species requires cavities in living pine trees for roosting and nesting that often take many years to complete, resulting in many incomplete excavations on the landscape. We used population monitoring data to show that orientation was stronger among completed cavities than incomplete cavities. There was a significant correlation between latitude and average cavity direction among populations, turning northward with increasing latitude, suggesting adaptation to local conditions. Long-term monitoring data showed that cavity orientation and breeding group size are correlated with egg hatching rates, fledging rates, and the total number of fledglings produced per nest. Our results provide empirical evidence from extensive long-term data that directional orientation in animal constructions is an important feature of the extended animal phenotype and have immediate implications for animal ecology and the conservation of endangered species.

Experimental evidence that nest orientation influences microclimate in a temperate grassland

“…There are few experimental studies of nest orientation (Ricklefs and Hainsworth 1969;Butler et al 2009;Landler et al 2014), most of which are from cavity-nesting species. This is unsurprising due to these species' readiness to occupy artificial cavities, which are an easy medium for orientation manipulation (Landler et al 2022). However, restricting experimental studies of nest orientation and microclimate to one nest type fails to account for the very narrowly constrained microclimates (35 °-37 °C) that are suitable for embryonic and nestling development relative to the broad range of weather conditions that nesting birds face.…”

“…Due to widespread associations between fledging success and orientation in directional nests, there is a strong potential for behavioral plasticity in orientation during nest building to influence fitness (Verbeek 1981;Lloyd and Martin 2004;Landler et al 2022). Such plasticity is good news for birds coping with reproduction under variable climatic conditions such as those experienced in the Great Plains of North America and elsewhere .…”