[Effects of the environment on health of feral pigeons (Columba livia)].

We examined 80 feral pigeons and their fecal samples from two feral pigeon lofts of the "Pigeon Action of Basel" (Switzerland) for different pathogens. The tested material harbored four pathogenic agents transmissible to humans (Chlamydia spp., Salmonella spec., Campylobacter jejuni, Cryptococcus neoformans) In addition several pathogens were found which are no zoonotic agents but potentially pathogenic for the pigeons themselves, such as Trichomonas gallinae, coccidia, helminths, ectoparasites and fungi. The number of pathogens and parasites detected in the fecal samples varied significantly between the two localities. The pigeons of the two investigated breeding flocks differed in nutritional status and the incidence of two species of feather lice, Columbicola columbae and Campanulotes bidentatus compar. The prevalence of Trichomonas gallinae between juveniles and adults was not significantly different but juveniles exhibited significantly heavier infestation if infected. Individuals with a good nutritional status tend to show heavier infestation with Trichomonas gallinae compared to birds with moderate or poor nutritional status. Birds with a poor nutritional status tend to suffer from a heavier infestation with the feather louse C. columbae, and birds with a good nutritional status show significant heavier infestation with C. bidentatus compar. It was remarkable that one of the two investigated breeding populations almost gave up its breeding activity for two years because of the loss of its familiar food source. Nevertheless, this population showed a better nutritional status than the population without restrictions in the acquisition of food. This fact could be interpreted by the existence of a biological control mechanism for suppression of the reproduction in degraded environmental conditions to ensure the survival of the adults. If this assumption is correct, the feeding of feral pigeons by animal lovers possibly causes impairment of pigeon's health in consequence of continuation of the breeding activity in spite of declined living conditions in the city.