Magnificent Frigatebird: Pirate of the Sky

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If you live in or if you’ve vacationed in southern Florida, there’s a good chance you’ve seen a Magnificent Frigatebird effortlessly soaring above. Since Frigatebirds rarely land, getting an up-close perspective of these graceful birds can seem impossible. This was the case for many of us working at the Florida Keys Wild Bird Rehabilitation Center until an injured female frigatebird was brought to us at the end of June. Found in Islamorada by our friend Maya Totman of Florida Keys Wildlife Rescue, the frigatebird was suffering from a broken right wing and fishing line entangled around its tail feathers. Our rehab team has done an excellent job treating its injuries and setting it on a trajectory toward recovery. Seeing this beautiful bird up-close has been an incredible experience that has allowed for a true appreciation of just how unique these birds are.

Magnificent Frigatebirds spend most of their life soaring over the ocean, never landing in the water. They’ll fly, on average, 129 miles per foraging trip and can reach altitudes of 8,202 feet (i). Soaring all day and night before landing is not uncommon. Swifts are the only other bird that will spend all night on the wing (i). Due to their lengthy foraging trips, Magnificent Frigatebirds do not exert much energy while flying. If you’ve ever watched one soaring high above, I bet you noticed its crawling flight speed and that it rarely flaps its wings. This is largely due to their reliance on tropical winds for speed and thermals for altitude changes. Their ability to consistently exploit these winds and thermals is a result of their exceptional anatomy. Although slender, Magnificent Frigatebirds have a wingspan that exceeds that of Golden Eagles. Their wingspan is large enough that they often have to begin and end flights from the tops of tall trees. However, it’s their high wing area to body mass ratio, which exceeds all other birds, that allows them to fly the skies endlessly (i).


Magnificent Frigatebirds are well known for being “aerial pirates.” They steal food from other seabirds by chasing and harassment which results in disgorgement of food by the stressed seabird. The frigatebird will then catch the food before it reaches the water surface. Despite this sinister strategy, Magnificent Frigatebirds catch most of their food themselves by plucking it off the ocean surface. They eat mostly fish, but they will also catch crustaceans, squid, jellyfish, hatchling turtles, and even young birds (ii)!

During breeding season, frigatebirds have a pretty incredible courtship displays. While on the ground or a tree, males will inflate their red throat pouch into a large balloon, shake their heads from side to side, quiver their wings, and clatter their bills while calling to a female flying overhead (iii). You may have seen a nature documentary with a British naturalist eloquently narrating this ritual from some exotic setting. If not, I highly recommend BBC’s The Life of Birds series, and not just the “Finding Partners” episode. In the meantime, the video below does a great job describing the flashy courtship display.

The effort put forth by males during courtship does not last throughout frigatebirds’ exceptionally long breeding season. When a breeding pair’s single chick reaches half size, the male frigatebird abandons his female partner and chick (iii). The female will continue feeding its young for a year during which time the male frigatebird can start his search for another mate (iii). As a result of this lengthy breeding season, females can only mate every other year.

Our female frigatebird has been eating well and her condition is continually improving thanks to the hard work of our rehab team. Be sure to periodically check our facebook page for updates on her progress. Next time you’re enjoying the outdoors in Florida or the Caribbean, see if you can spot a Magnificent Frigatebird soaring above looking for its next meal.

Steven Warchocki, FKWBC Intern, 2016

References

(i) Weimerskirch, Henri; Chastel, Olivier; Barbraud, Christophe; Tostain, Olivier (2003). Frigatebirds ride high on thermals. Nature 421 (6921): 333–334.

(ii) Audubon Guide to North American Birds: Magnificent Frigatebird

(iii) The Cornell Lab of Ornithology All About Birds: Magnificent Frigatebird

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