Crab Plover: Dromadidae
CRAB PLOVER: Dromadidae
Crab plovers range in size from 13 to 16 inches (33 to 41 centimeters) in height and 8 to 11.2 ounces (230 to 325 grams) in weight. They are mostly white in color, but have a black patch on the back and some black on the wings. The wings of crab plovers are long and pointed, and the wingspan, or the distance from wingtip to wingtip when the wings are open, ranges from 29 to 30.7 inches (74 to 78 centimeters). The tail is short and gray and the legs are long and blue-gray in color. Crab plovers have webbed feet and a strong first toe, which is used for digging nest burrows. Crab plovers have bills that are designed for eating crabs. These are large, heavy, black in color, and shaped liked daggers. Male and female crab plovers are generally similar in size and appearance, but males have larger, heavier bills. Young crab plovers differ slightly in coloration from adults, with gray on top of the neck, behind the neck, and on the wings.
Crab plovers occupy desert and semi-desert habitats, generally within 0.6 miles (1 kilometer) of the ocean. They require sand dunes for nesting.
Crab plovers are specialized feeders, that is, their diet includes only a few items. Crab plovers eat crabs almost exclusively. They hunt their prey by running after them in mudflats or shallow water and then stabbing them with their sharp, powerful bills. Small crabs are generally swallowed whole, while larger crabs are torn to pieces and then eaten. Both adult and young crab plovers eat crabs. Adults give young chicks bits of prey, and older chicks entire prey items. Other foods that crab plovers eat occasionally include other crustaceans, small fish, marine worms, and other invertebrates.
BEHAVIOR AND REPRODUCTION
Crab plovers are found in large groups throughout the year. They gather in large flocks of as many as hundreds of individuals to forage, or hunt for food. Crab plovers also breed in large colonies, digging their nest burrows close together in sand dunes. Roost sites, where birds rest, can include as many as a thousand crab plovers. The calls from these sites, described as a barking "crow-ow-ow" are sometimes heard as far as a mile (1.6 kilometers) away.
Some populations of crab plovers migrate during the year, traveling from one living area to another and back. Other populations remain in the same place throughout the year. All crab plovers are most active at dawn and dusk as well as at night, because their habitats tend to be extremely hot during the day.
Crab plovers are the only species in the order Charadriiformes (gulls, terns, plovers, and other shorebirds) that nest in underground burrows. Their burrows help provide a cool environment for adults, eggs, and chicks. Breeding in crab plovers generally occurs during the hottest months of the year, when outside temperatures can reach 104°F (40°C). Burrows also help protect young from potential predators.
Unlike many other birds, crab plovers nest during the hottest, driest times of year, generally between the months of April and June. Crab plovers time their reproduction so that there will be plenty of crabs available as prey when the chicks hatch. Because of the extreme heat, however, crab plovers build their nests underground, using their bills and feet to dig large burrows in sand dunes. Burrows measure approximately 47.2 to 74 inches (120 to 188 centimeters) long. Crab plovers are the only species in the order Charadriiformes (which includes gulls, terns, plovers, and other shorebirds) to nest in burrows. Burrows not only provide a cool environment for adults, eggs, and chicks, but help provide protection from potential predators.
Crab plovers are believed to be monogamous, with a single male breeding with a single female during the breeding season. However, as many as ten adult birds are sometimes seen at a single nest burrow, suggesting that some individuals may nest together, or that adult siblings may help their parents raise younger siblings. Females lay only one egg at a time. The crab plover egg is extremely large compared to the bird's body size. It is not known how long eggs take to hatch. It is also not known for certain whether both parents help raise chicks, but it is likely that only females are responsible for this task. Although crab plover young are precocial (pree-KOH-shul), hatching at an advanced stage of development, feathered and able to move, they remain in the burrow for a considerable length of time, being fed by adults.
CRAB PLOVERS AND PEOPLE
Crab plovers have little contact with humans because of the harsh climates they live in. However, in the past both crab plovers and their eggs have been eaten by humans.
Crab plovers are not considered threatened at this time, with surveys suggesting that there are as many as 50,000 individuals in existence. However, some populations have been affected by oil production activity, habitat destruction, pollution, and other factors.
FOR MORE INFORMATION
del Hoyo, J., A. Elliott, and J. Sargatal, eds. Handbook of the Birds of the World. Vol. 3, Hoatzin to Auks. Barcelona: Lynx Edicions, 1996.
Perrins, Christopher, ed. Firefly Encyclopedia of Birds. Buffalo, NY: Firefly Books, 2003.
"Crabplover." Bird Families of the World, Cornell University. http://www.es.cornell.edu/winkler/botw/dromadidae.html (accessed on April 20, 2004).
"Dromadidae (Crab Plover)." The Internet Bird Collection. http://www.hbw.com/ibc/phtml/familia.phtml?idFamilia=54 (accessed on April 20, 2004).