Cages Mitigate Predation on Eggs of Threatened Shorebirds: A Manipulative-Control Study

Beach-nesting birds (plovers; Aves; Charadridae) are impacted by many natural and human-induced threats (e.g., people trampling, dogs, and natural predators). In this regard, the use of anti-predator cages on their nests is effective in order to mitigate some of these pressures (i.e., predation). To evaluate the efficacy of anti-predator cages and the causes of nest failure in a breeding site of two species (Charadrius alexandrinus and C. dubius), we carried out a control-experimental design, comparing false nests (n = 69) in cages (experiment; n = 30) with false nests without cages (control; n = 39). We carried out the study in three seasonal periods (May, June, and July), controlling predations after three periods (three, six, and nine days) since positioning, recording the frequency of eggs still present and evidencing any predation event. The percentage of residual eggs was significantly higher in experimental nests when compared to control nests in all recording periods. Considering 59 predation events on false nests, the most important predators were: in experimental nests (n = 21) the fox, Vulpes vulpes (47.6%), and in control nests (n = 38), the hooded crow, Corvus cornix (50%). Our data suggest that the use of anti-predator cages significantly limits predation on eggs and therefore is likely to increase the hatching success in these ground-nesting birds independently in the seasonal period. However, also in the presence of a cage, the fox is a relevant egg predator