Effect of geographical latitude and sun exposure on Rufous Hornero (Furnarius rufus) nest orientation

Bird nest orientation is affected by environmental variables determined by their geographical position as well as microclimatic conditions. In closed-cup-nesting species, nests may be oriented to avoid adverse environmental extremes such as sun exposure, wind, and rainfall, although vegetal cover may provide extra protection generating random orientation patterns. Here, we assess nest entrance orientation in Rufous Hornero (Furnarius rufus) at 11 South American sites by comparing nests well covered by vegetation (> 75% covered) from those with less or non-external vegetal protection (< 25%). We estimated and compared mean entrance orientation between northern and southern locations and levels of vegetation cover using circular statistics (n = 1291). Additionally, the influence of geographical latitude and vegetation cover on nest orientation was evaluated using linear mixed models across sites with non-random nest-orientation patterns. Results showed differences in mean orientation values between covered and uncovered nests at most locations and directed entrance orientation for uncovered nests. On the other hand, the models indicate that nest entrance orientation is not affected by the joint effect of latitude and vegetation cover and high variability between locations. Local microclimatic conditions provided by the vegetation above nests are important determinants for nest orientation in the species, although additional information about local rainfall, wind, temperature, and nesting site availability may help to determine the factors affecting orientation in the species on a local level.