Infection alters foraging decisions in a common songbird

Abstract

The effect(s) of infection on optimal foraging decisions are largely unknown but have important implications for pathogen spread, especially when individuals congregate at or near food resources. House finches, Haeomorhous mexicanus, are ubiquitous group foragers whose visits to bird feeders facilitate the spread of Mycoplasma gallisepticum, which can cause severe conjunctivitis, temporary functional blindness and pronounced sickness behaviours. We placed single, wild-caught house finches in novel arenas containing a high-quality food source (sunflower seeds) and either a medium-quality (Roudybush crumble) or low-quality (5% sunflower, 95% rice hulls) food source. At one time point before infection and one time point during infection, we recorded each bird's latency to first visit each food source, number of unique feeding visits to each food source, total time spent feeding at each food source and the amount of each food source eaten. When presented with high- versus medium-quality food sources, healthy finches preferred high-quality food in terms of latency to first visit, time spent at the source and amount eaten. During infection, these preferences were lost or muted in all those metrics. When given a choice between high- and low-quality food sources, healthy birds still preferred the high-quality option, but, unlike with the medium-quality choice, this preference persisted during infection. These results suggest that finches' foraging decisions change based on infection status and available food choices. Such differences could mitigate contact rates and, therefore, pathogen transmission between healthy and sick individuals when food resources cause animal aggregation.