Food, shadow, and fire influence a tropical bird´s display

Abstract

Within social signaling contexts, behavioral displays used for territorial defense and courtship may be affected by vegetation characteristics and by human disturbance. The primary aim of this study was to evaluate the relation between motor display variables of the blue-black grassquit (Volatinia jacarina) and vegetation characteristics. Secondly, we tested if human disturbance (fire and grass mowing) could induce variations in display variables. We modelled two display variables involving conspicuousness and energetic motor investment (i.e., leap duration and rate) to examine their relation to habitat characteristics that reflect vegetation complexity (i.e., grass seed abundance, shadow intensity, vegetation density) and evaluated whether confounding factors (e.g., time of day, territory location and breeding status) influenced this relationship. In a second set of analyses, we assessed the influence of fire and grass mowing upon the bird’s display. We found that leap duration increased in contexts of high seed abundance and shadow intensity, and leap rate decreased along the day. Distance from display perches to vegetation patch edge or streets and the presence of an active nest did not predict displays variables. We also show that following a fire event, birds exhibited a lower display rate. Our results indicate that vegetation structure helps to shape the blue-black grassquit display, consistent with the interpretation that courtship exhibitions can signal territory quality. Our findings also show that anthropogenic disturbance can impact a bird’s sexual display and underscores the urgency of further studies about the effects of human activities on animals’ reproductive behaviors. Vegetation characteristics influence resource abundance and provide the backdrop for most animal activities. The degree of vegetation density can either facilitate or confound individuals’ daily activities, since vegetation density influences detection by mates, competitors, and predators. Human-induced habitat changes can influence animal communication by modifying vegetation structure and resource distribution. Our objective was to evaluate the relation between motor display variables of a tropical bird and vegetation characteristics and test if human disturbance could induce variations in display variables. We found that displays are influenced by seed abundance and shadow intensity, leap rate is highest at dawn, and fire reduces display rate. Our results indicate that vegetation structure helps in shaping this species’ sexual display. We highlight the lack of studies evaluating the influence of human activities on animals’ reproductive behaviors.