Factors affecting the prevalence of blood parasites of Little Owls Athene noctua in southern Portugal

We studied the relationships between occurrence of blood parasites and host traits in a wild population of Little Owls Athene noctua in Mediterranean habitats of southern Portugal. Of 39 owls captured between February and August 1999,16 (41.0%) were infected with Leucocytozoon ziemanni. One individual was infected with Trypanosoma sp. and another with a microfilaria. Age was the only variable influencing the prevalence of L. ziemanni in a multivariate logistic regression model: adults were more often infected than juveniles (82.4%, n = 17 vs. 9.1%, n = 22). This difference was probably due to the scarcity of appropriate vectors in the area at time of fledging. There was also a trend that infected adults owls had shorter bills than uninfected ones. This may indicate that infection may be associated with individual song characteristics of Little Owls, since a relationship between bill length and song features was found previously in the same area.