On the use of pharmacological sterilisation to control feral pigeon populations

The use of chemosterilisation for controlling feral pigeon populations was investigated by: (1) quantifying the reproductive activity of pigeons in two Italian cities; (2) testing the efficacy of nicarbazin, an anticoccidial drug with rapid and reversible effects on the reproduction of laying hens, on groups of paired pigeons maintained in open aviaries; and (3) simulating the effects of the use of nicarbazin on a hypothetical population, allowing for the reproductive productivity recorded in (1) and the efficacy of this drug as obtained in (2). Breeding attempts were recorded all year round in both study sites with a minimum peak in September–October, a maximum in March–July, but with active nests in winter too. In terms of the sterility activity of the drug, the results showed only a partial inhibition of reproduction of pigeons fed ~38–82 mg nicarbazin day–1 (kg bodyweight)–1 (500 and 800 ppm in feed), which, according to the simulations, would produce only a fleeting reduction of their abundance in the field. Data do not seem to support the use of this drug as an effective control method for feral pigeons, and they cast doubts on the opportunity to make use of chemosterilants, which produce only partial and reversible effects. The use of this drug could perhaps be considered only as part of an integrated pest-management program, which necessarily has to include the reduction of carrying capacity of the urban environment.