Universities
Summary
Data from a 3-year study of red-winged blackbirds (Agelaius phoeniceus) were used to test the hypothesis that parasites (in this case, haematozoa) reduce male fitness and cause diminished expression of secondary sexual traits, which, in turn, are used by females to select parasite-free males as mates. There was no evidence indicating a fitness cost to being parasitized because parasitized males were as likely as unparasitized males to acquire a territory and to survive from one year to the next.