Song as an indicator of parasitism in the sedge warbler

We studied female Choice and reproductive success ina marked population of sedge warblers, Acrocephalus schoenobaenus, from 1995 to 1996. Three genera of parasitic blood protozoans, namely Haemoproteus sp., Trypanosoma sp. an d Plasmodium sp., were identified from blood samples taken from all breedin g adults. Relatively high prevalence values of 19.5% in 1995 and 37.5% in 1 996 were associated with increased levels of white blood cells relative to the number of red blood cells. Compared with nonparasitized males, parasiti zed males had significantly lower repertoire sizes in both years of the stu dy, in one year, they also spent less time in song flights and weighed less . They also provisioned their broods at a lower rate. Parasitized females p roduced the same clutch size as nonparasitized females, although their broo ds were smaller at 7 days old. We suggest that haematozoan infections may r educe the expression of sexually selected song traits. Furthermore, such in fections may influence the standard of parental care provided by males; alt hough further research is needed to determine whether this is mediated thro ugh genetic resistance to parasitism or the effects of parasitism upon imme diate body condition. (C) 1999 The Association for the Study of Animal Beha viour.