Glowing brilliant white in the early morning tropical sun, graceful and balletic, I’ve recently added the white-tailed tropicbird (Phaethon lepturus) to my list of all-time favorite bird species for both their beauty and their interesting behaviors.

After photographing the birds every morning for almost two weeks on the coast of Bermuda, it would only take the sound of their courtship call for me to be rushing for my camera. I was addicted to watching and photographing their interesting behaviors as they renewed their monogamous bonds after being solitary nomads at sea for most of the year.

The mornings on the coast of SW Bermuda are quiet and radiant. Dark clouds (and rainbows!) are often on the horizon and the water glows a turquoise blue as the sun breaks around the cliffs.

Tropicbirds have striking white feathers, but in the soft, early light they reflect the color of the water on their wings and bellies. Later in the day, when the sun is stronger, the feathers have a burnished luster.

Biology. Tropicbirds can remain at sea for indefinite periods and can stay in the air for remarkably long periods of time. In the air these birds have a tern-like flight pattern with rapid wing-beats, but they also exploit their long wingspan and streamlined body shape to attain impressive altitudes by soaring upwards on rising thermals. While resting at sea, tropicbirds float on the sea surface, due to their waterproof plumage, and will take to the air again after powerful beats of the wings and thrusts of their webbed feet.

Quite graceful in the air, the tropicbird’s short, weak feet and backward-set legs cannot support their body-weight, limiting movement on the ground to an awkward shuffle with their webbed feet and by stabbing the ground with their sharp bill and hefting themselves along.

Mating. White-tailed tropicbirds have a intricate, ritualized courtship display – flying together, one bird slightly higher than the other and cocking its head to keep the lower bird in view, they synchronize their wing beats as they fly high into the clouds all the while chirping a distinctive call. As they climb, the bird above dips its elongated tail down and the bird below bends its tail upwards until they touch. Once they reach the apex of their climb, as high as 100 meters, they break apart and fly separate ways, only to repeat the pattern. No, they don’t mate in the air, but they do renew their bonds and come to the same nesting site each year to mate and lay a single egg.

Nesting. A single egg is laid and incubated by both the male and female at intervals of 13 days for around 40 to 43 days. Tropicbird parents use their large, webbed feet as an important heat source when incubating the egg.

Once hatched, the chick is largely left alone in the nest while the parents forage out at sea. It is at this time that the chick is most vulnerable to attacks, particularly from adults of the same or different species, which are looking for nesting sites. The single chick fledges after around 2 1/2 months in the nest, and join the adults in wandering as far as 1,000 kilometers out to sea in search of favorable feeding grounds. (1)

Although not strictly territorial, there is sometimes fierce competition for the best nesting sites and there may be bloody fights between birds, with stabbing, slashing and the interlocking of bills.

Juveniles. Often I saw 3 birds flying together. However, only 2 birds took part in the courtship flights. The third bird may have been a previous season’s offspring. White-tailed tropicbirds lay only one egg per season and juveniles take 2-5 years before reaching sexual and physiological maturity (2). This extended period may be needed to develop efficient methods of feeding and locating prey or for development of mating behavior and claiming a territory. The juveniles can be identified by a yellow bill that turns orange as they reach adulthood.

Feeding. When at sea for most of the year, the birds hunt during the day, diving with a rapid, vertical, spiraling plunge from 15–20 meters for flying fish and squid, and rest at night floating on the water. I observed them hovering (fishing?) above the coastal waves – they would swoop down and often get drenched with splashing ocean water, flying off and shaking themselves like a dog after a swim. They would also hover in front of the rocks and along the cliffs, perhaps feeding on the small crabs and periwinkles. Since adult Bermuda crabs are one of the main predators for their chicks (besides introduced cats and rats), it would be ironic if they were eating tiny crab hatchlings.

Distribution. White-tailed tropicbirds live in tropical areas and have a very complex life-cycle, scattered over deep, open ocean waters in the southern Indian Ocean and western and Central Pacific, as well as tropical and sub-tropical parts of the Atlantic Ocean and the Caribbean. They use pelagic areas for feeding and oceanic islands, such as Bermuda and the British Virgin Islands, for breeding. In the fall and winter (October–February) ranges extended as far west as North Carolina in the US and as far east as the mid‐Atlantic Ridge.

Conservation. The white-tailed tropicbird is protected by law at most key breeding sites, and has benefited from a number of conservation measures. On Bermuda, where the bird is the national symbol and known as the “long tail”, artificial nesting sites have been built into the sides of quarries, increasing the amount of available nesting habitat. A dedicated campaign to remove rats in Puerto Rico by trapping and poisoning has seen a significant increase in breeding success.

With a warming climate and sea level rise there has been increasing storm damage to nesting sites for the white-tailed tropicbird. Climate change may play a negative role in successfully raising chicks – both in the stability and safety of the nesting sites and in the abundance of food.

Citations

1. The breeding biology of White‐tailed Tropicbirds Phaethon lepturus at Cousin Island, Seychelles. Phillips, NJ. Ibis Vol 129(1) pp10-24, 1987
2. Breeding of White-tailed Tropicbirds (Phaethon lepturus) in the western South Atlantic. Leal GR, Serafini PP, Simao-Neto I, Ladle RJ, Efe MA. Brazilian J of Biol no76(3) 2016