In Season 1, Episode 4 of the Hunt, Attenborough describes how Magnificent Frigatebirds, Fregata manificens, take the opportunity to snatch flyingfishes when these poor fishes glide over the sea to avoid predation by mahi-mahi, the dolphinfish. Interestingly, as seabirds, frigatebirds seldom touch the ocean, because their feathers are not waterproof . However, they can travel over the oceans for months without landing, and they sleep as well as feed on fish during the long-distance transoceanic flight . How?
The majority of frigatebirds live in tropical or subtropical regions such as islands in the eastern Pacific Ocean or the Caribbean Sea, where most areas are covered by trade cumulus clouds [3-5]. Because trade cumulus clouds contain strong, high-speed turbulent updrafts, they are a nightmare for many human air travelers . However, for the frigatebirds, these clouds are the best vehicles to facilitate their travelling. Frigatebirds intentionally fly into trade cumulus clouds so that they are uplifted by the ascending air force within the clouds without any high energy cost [2, 5]. After they exit from the cloud, they glide at high altitude without flapping their wings until they meet the next trade cumulus cloud . This process requires much less energy compared to flapping wings constantly and traveling close to sea level. Additionally, stealing flyingfish from the battle between flyingfish and mahi-mahi, a behavior called interspecific kleptoparasitism , provides another opportunity to save frigatebirds’ energy instead of actively foraging for prey. Now you might ask how did frigatebirds evolved to take advantage of clouds for flying and stealing food from other species throughout their evolution history. Well, this question is waiting to be answered.
In the little time that they spend on land, frigatebirds also display many interesting behaviors. Although frigatebirds are opportunists, they are also good parents compared to most avians. During the mating season, like peacock’s males that exhibit fancy tails, male frigatebirds exhibit inflated red pouches to females, who then select their mates . Unlike many shore birds that are polygamous, having multiple mates per breeding season, frigatebird parents are highly monogamous and devote equal time when incubating their single-egg clutch [3, 7, 9]. Interestingly, although frigatebirds are long-distance travelers, they also have strong breeding philopatry, meaning that they will return to the same place they were born for mating and reproducing . However, the reason why frigatebirds have philopatric behaviors is still unclear.
by Siran Tian
The Hunt, Season I, Episode 4, starting at 4:50.
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