To kill a mockingbird: the combined effects of two radically different parasite

HERMAN JM; FIORINI VD; CRUDELE I; REBOREDA JC; PLADAS SH; BUSH S; CLAYTON D

Anchorage, Alaska

Congreso; AOS 2019 Meeting; 2019

Co-infection, or simultaneous parasitism by multiple parasites, can have significant consequences for host fitness. Still, research examining the effects of multiple parasites under natural conditions remains scarce, and many parasites that co-occur regularly in nature have been largely overlooked. Nest flies and cowbirds (genus Molothrus) are common parasites of breeding birds, and co-occur frequently in host nests throughout their ranges in the Americas. Independent studies of these parasites have reported significant reductions in host fitness due to parasitism, yet their combined effects on host fitness is unknown. In Argentina, chalk-browed mockingbirds (Mimus saturninus) are heavily parasitized by shiny cowbirds (Molothrus bonariensis) and the nest fly Philornis seguyi. During two field seasons in 2017 and 2018, we investigated how simultaneous parasitism by these radically difference parasites influences the survival of mockingbird nestlings. In 2018, we used action cameras to conduct constant daylight surveillance of nests to determine the exact cause and time of death. Using a two-factor design, cowbirds and Philornis were experimentally eliminated from mockingbird nests, resulting in four unique treatments. We found that mockingbirds in nests with neither parasite had the highest survival of all treatments, and the presence of either cowbirds or nest flies significantly reduced mockingbird survival. While we did not detect an interaction between the parasites, nests that were simultaneously parasitized by cowbirds and nest flies had the lowest overall fledging success. Our study shows that parasitism by cowbirds and Philornis has devastating effects on the survival of host nestlings.