Noisy and gregarious, the crab plover is commonly encountered in small groups foraging on the shore for its preferred prey of crabs (1) (2). These foraging groups usually comprise around twenty to thirty birds, but may number as many as 400 outside of the breeding season (2). The crab plover is active during the day and night (4), taking advantage of crabs, marine worms and mudskippers exposed by the receding tide (2) (4). This species’ large, powerful beak allows it to tackle crabs without suffering injury, swallowing smaller individuals whole, and smashing larger specimens against the ground, to be consumed piecemeal (2).
The breeding season occurs between April and August, at which time dense colonies form around areas that have an abundance of crabs on which the young can be fed (1) (3). The crab plover is unique amongst the waders for its habit of constructing its nest in an underground burrow (2). After moving inland from the shore to sand dunes, the birds excavate an extensive network of interconnected burrows, 1 to 2.5 metres long. The entrances of the burrows are initially angled downwards, before curving upwards and terminating in a nest chamber situated a short distance from the surface (1) (2). The burrow is believed to serve two important functions, one of which is to insulate the egg against the extremely high temperatures that occur during the breeding season (3) (5). The second function is that the chamber acts as a solar incubator, keeping the egg at an optimum temperature, which means that only a small amount of direct incubation by the parent birds is necessary (5). A single white egg is laid, which is very large and provides the developing chick with sufficient energy that after the 32 to 33 day incubation period it hatches very well-developed and is quickly able to walk (2) (3). Despite this fact, the chick remains in the nest chamber until fledged, where it is fed live crabs by both parent birds (2).
After the breeding season, some crab plovers remain in the vicinity of the breeding colonies, while the majority fly southwards or eastwards to wintering sites around the Indian Ocean. Interestingly, while surveys of birds at the wintering sites appears to indicate that this species could have a global population of between 60,000 and 80,000 birds, the total population at the known breeding grounds represents only a fraction of this figure. Hence, there must be some large breeding colonies of crab plover that have yet to be discovered (3) (6). Most recently, in a survey conducted between 2002 and 2004, the largest colony yet discovered was found in the Dahlak and Howakil archipelagos, off the coast of central Eritrea. However, while this comprised an estimated 4,800 to 6,500 individuals—half of the known breeding population—it still does not account for the large numbers of birds observed at the wintering grounds. The authors of the study therefore speculate that the missing colonies probably lie in southern Eritrea, Sudan and Somalia (6)