Sex differences and breeding ecology of a burrow-breeding shorebird, the Crab Plover Dromas ardeola

The Crab Plover Dromas ardeola is endemic to the Indian Ocean basin and breeds on islands around the Arabian Peninsula. Unique among shorebirds, it nests in an underground burrow where it lays a single white egg and feeds one chick. We investigated sex-related differences in body size and parental care of this species in Saudi Arabia. Molecular sexing of DNA samples of 66 adult Crab Plovers indicated that 26 were males and 40 were females. Males had significantly longer bill, wing and tarsus lengths than females, confirming previously published reports on sexual size dimorphism in Eritrea. Observations of molecular-sexed adults at four nests showed that both parents fed the chicks; however, females brought food to the nest-burrow more often than males (67.6% of all cases). We found that the temperature inside active nesting burrows was relatively stable at 35.0 ±SE=0.18°C (n = 11 nests) regardless of ambient temperature just outside the burrows. This suggests that burrows serve a purpose in incubation as well as in defence from predation. In the colony, adults were seen to prevent chicks from multiple burrows from leaving the nest when their own parents had left the colony, confirming a helper breeding system. We suggest areas for future investigation to further elucidate the breeding behaviour of this enigmatic and unique burrowing shorebird.