INTRACOLONIAL DIFFERENCES IN THE INFESTATION BY HAEMOPROTEUS-LARI ON YELLOW-LEGGED GULLS LARUS CACHINNANS

The prevalence and intensity of Haemoproteus lari infestation were stu died in a colony of Yellow-legged Gulls (larus cachinnans) on the Mede s Islands (NE Spain) during 1994 and 1995. Prevalence did not differ b etween years, sexes, clutch sizes or nesting habitats. More heavily in fected females tended to ray smaller clutches and to be in a leaner bo dy condition; in males, intensity of parasites was unrelated to their dutch size and their body condition. These results are partially consi stent with the detrimental effect of brood parasites, but also with a tendency for stressed birds to relapse. Intensity of parasitemia diffe red both between years and among nesting habitats of the gullery, prob ably as a result of differences in bird quality at the time of samplin g. We suggest that these effects should be controlled for in studies d ealing with parasites in colonial nesting birds.