Merlin

Royal Tern Life History

Habitat

Habitat Shorelines

During their entire life cycles, Royal Terns inhabit warm coastal marine waters, and they normally rest and forage very near shore. When feeding young, they may venture well offshore, occasionally over 50 miles; or head inland along saltwater bays and rivers. Royal Terns sometimes show up in interior North America following hurricanes.

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Food

Food Fish

Royal Terns eat mostly small (2–4-inch) fish and shrimp, which they capture by flying 20–30 feet above the water and plunge-diving to seize prey in the bill. They forage singly, in small groups, or in large groups of hundreds of birds, often among other seabird species, normally over shallow water. After capturing a prey item near the water’s surface, they rise up quickly and continue flying, usually swallowing the item while in flight, sometimes after manipulating it in the bill to soften it. Royal Terns eat many types of small, surface-schooling fish, including silverside minnows, anchovies, sardines, menhaden, bluefish, butterfish, and drum. In the Caribbean, they take small flying fish. In the mid-Atlantic regions, they prey heavily on small blue crabs when the crabs are molting (“soft-shell crabs”). They may also feed at night on squid, which rise to surface waters only in darkness.

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Nesting

Nest Placement

Nest Ground

Male and female select a ground nest site on a sandy beach, barrier island, or dredge-spoil island.

Nest Description

Nests are small, unlined depressions in the sand, made by digging with the feet and finishing the shape with the belly. Adults defecate around the nest rim.

Nesting Facts
Egg Description:Whitish to brown, heavily spotted around large end.
Condition at Hatching:Eyes open. Covered with down and able to leave nest within one day.
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Behavior

Behavior Aerial Dive (water)

Royal Terns nest in dense colonies. They tolerate others of their species except during the height of courtship, when males are prone to squabbling with each other. Like other terns, Royals court both in the air and on the ground. In the air, male and female make high, spiraling flights, with the male often giving the female a fish in midair, with much calling. On land, males present interested females with a small fish, crab, or shrimp, while calling, then bow to the females, raising the crest. Once paired, the two come close together, head to tail, and begin to walk in a tight circle together, then often strut side by side through the colony. Often these courtship displays attract the interest of a third tern, a male in most cases. Aggressive displays between rival males involve raised crests, drooped wings, and rapid movements of the head, along with calling. This species appears to form monogamous pairs. Males feed females during courtship and incubation, and also help incubate the eggs. When feeding young chicks, Royal Terns sometimes peck at or chase away chicks of neighboring pairs that wander into their nest territory or try to beg for food. As the chicks grow larger and become more mobile, the adults gather them into a crèche (a tight group), and most aggression subsides. Both parents feed their chick well after it fledges and accompany it south to wintering areas, where young birds may still beg food from a parent 8 months or more after hatching. In the nonbreeding season, Royal Terns remain social and often join flocks of other terns or gulls.

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Conservation

Conservation Low Concern

Royal Tern populations in North America were stable overall or possibly increased between 1966 and 2015, according to the North American Breeding Bird Survey, although they showed sharp declines in Florida. Partners in Flight estimates a global breeding population of 250,000 and rates the species an 11 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. The North American Waterbird Conservation Plan estimates a North American breeding population of 100,000-150,000 birds. Royal Terns are very sensitive to disturbance at nesting colonies and may abandon them if people, dogs, or predators approach too closely. As human populations grow and gather on beaches in increasing numbers, colony disturbance can become a serious problem. Some colonies that once occupied barrier island beaches have moved to artificial dredge-spoil islands for nesting, but these too have attracted humans and their pets in recent years. A separate concern is the erosion and loss of coastal islands to rising sea levels, which further limit potential nesting areas for this species. Climate change, with increasingly frequent and more destructive tropical storms, is likely to threaten this species and many other seabirds.

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Credits

Buckley, P. A. and Francine G. Buckley. (2002). Royal Tern (Thalasseus maximus), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Kushlan, J. A., M. J. Steinkamp, K. C. Parsons, J. Capp, M. A. Cruz, M. Coulter, I. Davidson, L. Dickson, N. Edelson, R. Elliott, R. M. Erwin, S. Hatch, S. Kress, R. Milko, S. Miller, K. Mills, R. Paul, R. Phillips, J. E. Saliva, W. Sydeman, J. Trapp, J. Wheeler and K. Wohl (2002). Waterbird conservation for the Americas: The North American waterbird conservation plan, version 1. Washington, DC, USA.

Lutmerding, J. A., and A. S. Love (2017). Longevity records of North American birds. Version 2017.1. Patuxent Wildlife Research Center, Bird Banding Laboratory, Laurel, MD, USA.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2017). The North American Breeding Bird Survey, Results and Analysis 1966–2015. Version 2.07.2017. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, USA.

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