Parasitic flies (Philornis spp.) and offspring prospects in three passerines in a southern temperate forest of Argentina

GONZALEZ, EXEQUIEL; JAUREGUI, ADRIÁN; SEGURA, LUCIANO N.

ARDEOLA

SOC ESPANOLA ORNITOLGIA

Año: 2022 vol. 69 p. 3 - 20

0570-7358

Philornis flies exert strong negative selection on avian host life histories; but their possible influence remains poorly studied at the southern limits of parasite distribution. Here we collected data during three consecutive breeding seasons of Philornis parasitism (prevalence, intensity and latency) in the Masked Gnatcatcher Polioptila dumicola, the Vermilion Flycatcher Pyrocephalus rubinus, and the Blue-and-yellow Tanager Pipraeidea bonariensis in a south temperate forest of Argentina. We hypothesize that Philornis parasitism will negatively influence infected nestlings. In this sense, we predicted that there will be a negative relationship between both nestling growth and survival with the presence of parasites. In considering the body size differences among nestlings of these three host species, we predicted that nestling survival in parasitized nests and parasitism intensity per nestling will be greater the larger the species, and that the number of growth parameters that differ between parasitized and non-parasitized nestlings will be greater the smaller the species. We monitored 564 nests and found prevalence to be 16.7% for the Masked Gnatcatcher, 30.1% for the Vermilion Flycatcher, and 37.9% for the Blue-and-yellow Tanager. Parasitism increased during the season for all three species. As predicted, nestling survival was lower in parasitized nests (~30%) than in non-parasitized nests(~90%) for the three species, and there was at least one body measurement for each species, from which one or more growth parameters were significantly lower for parasitized nestlings compared to non-parasitized nestlings. We found partial support to our prediction relating to host body size because differences only emerged in parasite intensity of nests that produced fledglings, as well as in the extent of growth parameters affected. This is the first study providing detailed data of Philornis fly parasitism and how this parasite affects the fitness of three bird hosts at the southern limit of the parasite?s distribution.