Effects of Haemoparsite Infection and Food Supplementation on a High Elevation Passerine Bird

Abstract

Strong circumstantial evidence from laboratory and theoretical studies suggests that sublethal parasite burdens can influence host population dynamics whether acting alone or in conjunction with reduced food availability. The significance of these effects has rarely been examined in natural environments. This study aims to examine the interactive effects of avian malarial haemoparasite infections and food supplementation in a food limited free‐living population of Mountain White‐ crowned Sparrows (Zonotrichia leucophrys oriantha) breeding in Gunnison National Forest, Gothic, CO. To analyze the effects of haemoparasites (Plasmodium, Leucocytozoon, and Haemoproteus) and food supplementation on multiple aspects of reproductive success, we analyzed blood smear data (to determine infection status) and manipulated sparrow food availability. During the early breeding season, when natural food availability is especially scarce due to residual snowpack and frequent spring snowstorms, supplemental food was provided on select plots. We quantified the impact of haemoparasite infection and food supplementation on reproductive success by evaluating: daily nest survival (DNS), clutch size, probability of the clutch hatching, probability of the nestlings fledging, and offspring quality. Our data underscore the impacts of avian malaria on the reproductive success of a free‐living avian population where malaria is endemic. Most of the negative effects of malaria infections are observed in young‐rearing phase. In addition, we documented a supported strong positive effect of food supplementation, which however was restricted to the incubation phase. There was no effect of infection or food supplementation on clutch size, or on the quality of the fledged (quantified as young mass or tarsus length). Interestingly, we did not detect any interactions between food supplementation and blood parasite coinfection in any metrics of reproductive success, daily nest survival, or offspring quality.