EFFECTS OF BLOW FLY (PROTOCALLIPHORA-SPATULATA, DIPTERA, CALLIPHORIDAE) PARASITISM ON THE GROWTH OF NESTLING SAVANNA SPARROWS IN ALASKA

We investigated the effect of blow fly larvae (Protocnlliphora spatula ta) on nestling savannah sparrows (Passerculus sandwichensis) in Alask a subject to biennially fluctuating prey abundance. Grasshopper popula tions in some regions of interior Alaska can show a strong biennial pe riodicity. Growth of nestling savannah sparrows, numbers of blow fly l arvae in nests and on nestlings, and grasshopper populations were moni tored during four breeding seasons (1990-1993) on the Delta Agricultur e Project site near Delta Junction, Alaska. Growth parameters for para sitized and nonparasitized nestlings were compared within and between years. There were no significant differences in growth parameters betw een parasitized and nonparasitized nestlings between any years. There were also no differences in growth parameters within years, except for tarsus length in 1991 and nestling mass in 1993 (low grasshopper year s); in 1993, parasitized nestlings were heavier and the sample size wa s small. Additionally, there were no differences in fledging success w ithin years. Although parasitism combined with other factors (e.g., fo od limitation) may have an impact on avian reproduction, our data do n ot support this.