Nest Orientation in Closed Nests of Passeriformes across a Latitudinal Gradient in the Southern Neotropic

Abstract. Birds are expected to orient their nests non-randomly in order to avoid extreme thermal conditions that are known to affect their reproductive success. Considering the hypotheses that yearly mean temperature influences entrance orientation in birds, nests at higher latitudes are expected to face the equator in order to take advantage of warmer temperatures. Here we explore the relationship between latitude and nest entrance orientation in closed nests of Passeriformes in the southern Neotropics (Furnariidae, Rhinocryptidae, Troglodytidae, Tyrannidae), using both published and original data. We found a positive and significant correlation between mean entrance orientation and latitude, and report significantly non-random nest orientation at 62% of the locations with available samples. Overall, there is a trend for nests at lower latitudes to have north-northeasterly orientations, and for nests at higher latitudes to be oriented northwest. The reasons for the observed trends remain unclear, but likely involve the availability and intensity of solar radiation and its effect upon the nest microclimate.