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This graceful seabird is often seen flying over coastal waters. Image credit: HOBBYFOTOWIKI/WIKIMEDIA COMMONS
Around the world, Royal terns are admired for their strong but gentle acrobatic flight. These bright white birds move quickly from spot to spot on long, pointed wings, and a deeply forked tail at the end of a sleek body allows them to hover just as easily before plunging into the surf to grab a small fish or shrimp. In the Americas, we have four terns with large black head crests: the Caspian tern, Elegant tern, Sandwich tern and—our pick—the gre-garious Royal tern (Thalasseus maximus).
Royal terns are a common sight on parts of both the Atlantic and Pacific coasts of North, South, and Central America, and the Caribbean islands. They sport a large orange bill (they’re sometimes called “carrot bills”) and a large spiky-looking black crest at the back of their head. After the breeding season, the top of their heads turn white leaving a ring of black that brings to mind a bald man with a circle of hair above his ears.
Royal terns migrate south for the winter and form pair bonds as they return north for the nesting season. They nest in colonies that can have more than 20,000 birds, so pairing before they arrive is easier than trying to find a mate in the crowd.
Nesting colonies form on barrier islands, dredge spoils, and sand spits, keeping them safe from most land predators. When it is time to nest, males and females work together to choose a site. The colo-ny is dense and nests are just a few inches apart, so finding an open spot can take a while. They walk around, twist their heads so that each eye can ex-amine a likely spot, and scrape the sand with their partially webbed feet to test the base. When they find the right place, they tuck their heads between their legs to get an unusual close-up view, test the site again by kicking a little more sand, and snuggle into the ground to wiggle and form a body-sized de-pression. The terns don’t add a soft lining of grasses or feathers to the nest, but they do add a unique twist by pooping around the perimeter to make a wall around the site that hardens in the sun.
The hen then lays a single egg in the depression and the pair take turns incubating the egg, but it’s not necessarily a full-time job. Parents will fly as far as 25 miles to find food and socialize with other terns, leaving their egg exposed for several hours a day. This works for terns because the egg is protect-ed by the thousands of other birds in the colony. When they return, they quickly find their own nest, recognizing it by the color and pattern of the egg—an amazing feat in a sea of white birds.
After 30 days of incubation, the egg hatches and a tan and gray, grubby-looking bird with an overly large bill and feet lies in the bottom of the depres-sion. It doesn’t take long for the chick to dry and for the parents to start bringing food to the nest.
Chicks don’t stay in the nest for long. One or two days after hatching, they leave the nest permanent-ly to join hundreds or thousands of other chicks of all ages in a mass nursery called a creche. Parents still spend several hours a day away from the chick, but there are always adults around watching over the crowd. When the parents return, they find their chick by recognizing its voice among all the calls in the creche—another amazing feat.
Caught in courtship. Royal terns court with bold, coordinated displays, shifting from aerial flights to ground-based rituals that help establish lasting pair bonds.
Image credit: KeenanHye / Wikimedia Commons
After another 30 days in the creche, the young birds are ready to leave. Juveniles and parents head north briefly before turning south for the winter. Young birds are not as graceful as their parents in flight, and their fishing skills are poor, so they rely on the adults for food. Eventually, the family makes its way to more tropical shores to rest in the sun. The parents continue feeding the young on the win-tering grounds, but when breeding season comes again, the parents head north and the juveniles are on their own. Immature birds stay on the wintering grounds for another year or two. There is no rush—the oldest known Royal tern was banded in North Carolina and found 301/2 years later in Belize—so there is plenty of time to start the next generation.
A quiet moment resting in between long-distance flights.
Image credit: Eyelovebirds / Wikimedia Commons
Fish serve a dual purpose for this seabird, making up the bulk of its diet and playing a role in courtship, when males present fish to females.
Image credit: Gary T. Leavens / Wikimedia Commons
A first-year royal tern captured on a beach.
Image credit: Gary T. Leavens / Wikimedia Commons
MEASUREMENTS (in mm)
| Wing | Tail | Tarsus | Culmen | |
|---|---|---|---|---|
| Female | 357.7 | 144.3 | 32.4 | 62.8 |
| Male | 367.7 | 167.2 | 32.9 | 65.0 |
Adapted from Buckley, P. A., F. G. Buckley, and S. G. Mlodinow (2021).
REFERENCE
Buckley, P. A., F. G. Buckley, and S. G. Mlodinow (2021). Royal Tern (Thalasseus maximus), version 1.1. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.royter1.01.1