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Aerial Robbers

It was a spectacular sight to see the kettle of Red-billed Tropicbirds circling high above the bay at Little Tobago Island. In the blink of an eye we heard air shredding as a Magnificent Frigatebird dove upon a Tropicbird. The steep dive ended with the Frigatebird grabbing the Tropicbird’s tail and giving it a firm shake. My first thought was that tropicbirds were too large to be a prey item for the Frigatebird. As we watched the dramatic scene, it dawned on us that the Frigatebird was not after the tropic bird; instead the Frigatebird was trying to get the tropicbird to regurgitate its stomach contents in midair. We were watching kleptoparasitism.

Kleptoparasitism is stealing food from other birds and is not the only way Frigatebirds feed themselves. Frigatebirds opportunistically take chicks out of seabird nests or grab hatching sea turtles. They also fish by skimming the surface and grabbing fish just under the surface. They are often seen behind fishing boats dipping for fish or offal thrown over by the fisherman.

Have you ever watched a Frigatebird fly? They are the ultimate gliders. Frigatebirds are said to have a greater wing span to body weight ratio than any other bird, allowing them to soar for days with little energy expenditure.

Frigatebirds cannot swim, and walking on land or taking off from the water is quite difficult. Their long, forked tails allow these aerial masters to turn, duck and dive in order to rob the prey from other seabirds. In flight, the forked tail often will appear as one long pointed tail.

Adult male Magnificent Frigatebirds are all black with a red gular, or throat pouch, that is inflated during the breeding season to attract a mate. The gular pouch is rarely seen outside of breeding season. Adult females are black with a white breast and the immature birds have a white head and breast. During breeding season, males inflate their gular pouches until they look like red, heart-shaped balloons. Courtship is a noisy affair with the males making a rattle or drumming sound with their gular pouches, clacking their bills and vibrating their extended wings.  Females encourage the courtship chaos by giving their attention to the males presenting the greatest show of noise and largest gular pouches.

Frigatebirds nest colonially. A rough nest is constructed in low trees or on the ground on remote islands. A single egg is laid each breeding season. The Magnificent Frigatebird is found in the Caribbean and along the coasts of north and South America. Worldwide, there are five species of Frigatebirds.  The Magnificent Frigatebird is the only one of the species we see in the Caribbean.

Across its range, the Magnificent Frigatebird is declining. Destruction of mangroves and other seaside vegetation are causing a loss of nesting habitat.
 
Devi Sharp is a retired wildlife biologist and is exploring the birds of the Caribbean with her husband, Hunter on their sailboat Arctic Tern.

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