Haematozoa of British birds VIII. Blood parasites of migrants, particularly the willow warblerPhylloscopus trochilus

Summary The results of a four year study of haematozoa in Palaearctic migrants, particularly Phylloscopus trochilus, at Tring are reported. Of 379 P. trochilus examined 11·3% were infected. Haemoproteus and Leucotytozoon were observed in adult birds returning in the spring and Atoxoplasma was the only parasite occurring in juvenile birds. Observations on re-trapped birds showed that patency quickly diminished into a latent phase and emphasized further the importance of migration in acquiring most haematozoan parasites.