Blood parasites, sexual selection and reproductive success of European kestrels

The Hamilton-Zuk hypothesis (HZH) of sexual selection postulates that parasites could induce heritable fitness dif- ferences that are a cue for female mate choice. The Resource Provisioning hypothesis (RPH) says that females mate with unparasitized males to acquire resources, such as male parental care. Blood was randomly sampled from 113 individual females and 94 males among 148 kestrel (Falco tinnunculus) pairs breeding in western Finland during 1991-1993. The most common haematozoans in the blood films were Haemoproteus tinnunculi (overall prevalence 40% for females and 25% for males) and H. brachiatus (13% and 10%). Adult (≥ 2-year old) males with bright tail feathers had a higher load of H. tinnun- culi than dull-tailed males. Intraspecifically, HZH predicts an inverse relationship between the expression of a secondary sexual trait and parasite load, but adult males with bright back and tail colours (a cue for female mate choice) were not less parasitized with haemoproteids than dull males. HZH also predicts a negative relationship between the host fitness and its parasite load. Partners of haemoproteid infected adult males started to lay eggs later and produced smaller clutches than part- ners of non-infected adult males (mean laying date 9 May versus 4 May; mean clutch size 5.2 versus 5.7 during 1991-1993). Infected males may diminish their investment in courtship feeding, because they may be less vigorous than non-infected males. The reduced fitness of infected males may then not be a consequence of genetical dissimilarities in parasite resistance, but instead a consequence of inter-male viability differences that affect the acquisition of resources that are invested in costly clearance of parasites and parental care. This appears to support the prediction of RPH that females gain parental care by choosing unparasitized males.