Temporal variation in the detection of endangered birds in the Northern Atlantic Forest

ABSTRACT The detectability of birds may shift seasonally in response to changes in environmental conditions and social interactions. Seasonal variation in bird behavior may influence the findings of avifaunal inventories, by making it difficult to detect some species, especially the rarest ones. We investigated how variation in rainfall patterns affects the detection of bird species in a fragment of tropical forest in the most threatened region of the Brazilian Atlantic Forest, in its northern extreme. The data were collected between January and September 2018, and October to December 2019, during which, two observers walked transects within a forest fragment. Considering the complete set of species studied, detection correlated negatively with rainfall, with a decrease in detection of bird species two months before the onset of the rainy season, between February and June. We identified distinct patterns of variation in bird detection. While 10 bird taxa were detected throughout the year, others were detected more frequently during the dry season, or at the onset of the rainy season. A positive correlation was found between rainfall and the detection of Momotus momota marcgravianus Pinto & Camargo, 1961, Xiphorhynchus atlanticus (Cory, 1916), and Xenops minutus alagoanus Pinto, 1954. Negative correlations, with reduced detection, were found in relation to the onset of the rainy season in the detection of Hemitriccus griseipectus naumburgae (Zimmer, 1945) and Chiroxiphia pareola (Linnaeus, 1766). The combined detection of these species was more frequent between the peak of the dry season and the onset of the rainy season. We recommend scheduling future surveys in the study region during this period to maximise the likelihood of detecting the greatest number of species.