Cardinal orientation of cavities excavated by birds in the neotropics: relationship with macro-environmental attributes

The microclimate of avian nest and roost sites affects reproduction and survival; therefore, environmental placement of these structures is of adaptive significance. It has been hypothesized that, to optimize thermal properties, at higher latitudes avian excavators should orient their cavities more toward the equator. In support of this, a meta-analysis of cavity entrance orientation of Northern Hemisphere woodpeckers showed that with increasing latitude cavities were oriented more toward the south. We tested this hypothesis, with the inverse prediction (dominance of north orientations as latitude increases), for cavities excavated in the Southern Hemisphere, with data from nine Neotropical ecorregions, including tropical to subpolar sites (~16-55° S, ~48-72° W). We recorded orientations for nests and/or roosts (n=1511) excavated in trees, poles, and terrestrial termite mounds by 25 species varying in size, from Picumnus to Campephilus. Based on several generalized linear models, we found that macro environmental variables (such as altitude, latitude, or ecorregion) failed to predict orientation. Cavities were randomly oriented in Cerrado, Chaco, Atlantic Forest and Pampas ecorregions. However, they were non-random in Yungas and Monte (facing west-southwest), Espinal (north), Valdivian (east) and Magellanic (north-northeast) ecorregions. These results do not support the prediction that at higher latitude birds orient their cavities more toward the equator, and cast doubt on latitude as a global driver of cavity orientation. Other macro-environmental variables (such as reduced continentality in the southern Neotropics) might cancel out the effects of latitude. Further, local variables may explain the patterns occurring at each ecorregion.