Abstract
Ectoparasite fauna of Falco vespertinus breeding colonies was investigated in a system of artificial nests in the Po valley (Parma province), Italy, during four subsequent breeding seasons (2019–2022). Conservation actions regarding Falco vespertinus led to a great increase in its presence in the area. This rise was believed to coincide with an increase in the prevalence of hematophagous ectoparasites breeding in the nests, with a potential negative impact on the attractiveness of the breeding site. Ectoparasites collected from the nestlings’ bodies almost entirely belonged to a single species, Diptera Carnus hemapterus, with a quite variable prevalence in different years. Maximum ectoparasite load was consistently linked to younger than two weeks old chicks. Carnus hemapterus may pose a threat to less resilient specimens of Falco vespertinus because it feeds on live tissues, increases metabolic expenditure, and can introduce blood parasites. Nonetheless, this species is part of the ecosystem shared with the falcon and might have a conservational value itself. We propose that higher occurrence of this ectoparasite might be linked to diet parameters, especially the availability of small mammals and the lingering of prey remnants in the nests, as well as to the age of the parasitized nestlings. These findings might have important implications for the conservation of this rare Falco species.