Food abundance explains the breeding season of a tropical shorebird, the Crab Plover Dromas ardeola

The timing of breeding in birds is a life-history trait that generally depends on food availability, but other factors may play a role, particularly in tropical areas where food availability is less seasonal than in temperate or polar areas. We studied the factors affecting the breeding season of the Crab Plover Dromas ardeola, a burrownesting colonial shorebird endemic to the north-western Indian Ocean. A reduced risk of burrow flooding, high temperatures suitable for exploiting solar incubation, a reduced interference by Palaearctic shorebirds during foraging, a reduced risk of predation by Palaearctic raptors and a high food abundance are all associated with the summer breeding season of the Crab Plover in our study area in Eritrea. In addition, we collected remotely recorded data associated with these advantageous environmental factors around breeding colonies in nine well-separated areas. Only average annual chlorophyll a concentration, a proxy of marine productivity, was significantly correlated with the start of the breeding season, which varies up to one month throughout the breeding range. We conclude that food abundance, with the likely high intraspecific competition due to coloniality, is strongly supported as the critical factor determining the nesting phenology of this tropical species.