Hard to handle: infected house finches do not prefer easier-to-consume food

Food-handling time, or the time elapsed between capturing a food item and consuming it, is a key factor in foraging decisions. For example, quickly consuming more items that are easier to handle, but of lower nutritional value, can be more beneficial than attempting to consume items that are harder to handle but more nutritious. Infection likely alters such foraging decisions, as sick animals often express sickness behaviours (lethargy and anorexia), which could affect both motivation and foraging proficiency. Although such changes could alter interindividual contact rates at food patches, and thus pathogen spread, little is known about how infection alters food preferences and handling times among wild animals. We investigate this question in house finches, Haemorhous mexicanus, infected with Mycoplasma gallisepticum (MG), which causes conjunctivitis and is commonly transmitted at bird feeders. We inoculated wild-caught, captive finches with either MG in Frey's medium or only Frey's medium and provided a 50:50 mixture of equally nutritious whole sunflower seeds and sunflower seed kernels, food items with longer and shorter predicted handling times, respectively. We then assessed handling time, the number of foraging attempts and foraging success (consumed-dropped). As predicted, both groups took longer to handle whole seeds than kernels. MG-inoculated birds, however, showed longer handling times overall and spent disproportionately more time handling whole seeds than did sham-inoculated birds. Both groups were more successful at handling the easier-to-handle kernels than whole seed. However, only sham-inoculated birds showed some indication of making more total foraging attempts on kernels than whole seeds; MG-inoculated birds appeared to make a similar number of attempts on both foods. These results suggest that infection could reduce a preference for easier-to-consume items. More broadly, they show that MG-inoculated and sham-inoculated finches show different foraging behaviours, which could impact where they forage in the wild, potentially reducing contact and the probability of pathogen transmission.