Caspian Tern
The largest tern in North America
The largest and most cosmopolitan tern in North America, the Caspian tern (Sterna caspia) was first described by Prussian zoologist Peter Simon Pallas in 1770 as he explored the Caspian Sea in southern Russia. This is a very large gull-like tern with a sizable, stocky, red-orange or red bill. It has white underparts, black feet and legs, and a slightly forked and white tail. The back and wings are pearl gray. Nonbreeding birds have a dusky crown and forehead, while breeding birds have a black cap that extends over the eyes and forehead. It is about 20 inches long with a 52-inch wingspan.
Juvenile birds are more mottled above, the bill is duller and more orange than the adult with a blackish tip, and the crown of the head is more heavily streaked with white. This tern resembles a royal tern (S. maxima), but the Caspian tern is more massive, the bill is much stouter and a deeper orange, and the wings are much wider.
Nonbreeding and wintering Caspian terns are widely distributed in Florida. This tern can be observed along both coastlines year-round, as well as in the interior of Florida. It is a permanent resident of peninsula Florida but rare in the Panhandle, remaining absent from the western Panhandle in the winter.
The Caspian tern has a disjunct breeding range including the western United States, Gulf Coast, southern Alaska and south-central Canada. The creation of dredged-material spoil islands along the coasts of Florida created breeding habitat for the Caspian tern. It was first observed breeding in Florida in 1962, but it remains a rare occurrence. It has been observed breeding at a few coastal islands from the eastern Panhandle southward mostly at Tampa Bay, where 65 pairs nested on a spoil island in 1988 on the Hillsborough County side. Annual nesting has persisted in Hillsborough Bay. This species used to breed in Brevard, Charlotte, Franklin and Pinellas counties, but these colonies no longer exist. During the 1970s 31 pairs nested at Merritt Island National Wildlife Refuge, but this colony has not persisted. In Florida they generally breed with laughing gulls (Laurus atricilla).
The dredge material of the coastal spoil islands where these terns breed affords protection from terrestrial predators and recreationists. The Caspian tern nests in Florida from April through August. The substrate it requires for nesting includes shell hash, gravel and sand. Many of Florida’s spoil islands are heavily vegetated and not suitable for the Caspian tern because for breeding it requires unvegetated substrates.
It uses sandbars, beaches and islands for loafing and roosting. It forages for prey over inland impoundments and lakes, rivers, flooded agricultural fields, mudflats and coastal bays, feeding mostly on fish. In flight it hovers before diving for targeted fish.
Recently there has been a decline in the Caspian tern’s foraging habitat as a result of red tide and poor water quality in many areas. Roosting habitat on islands, beaches and sandbars has also declined because of the increasing number of beach-goers and boaters. People visit islands for fishing, camping, shelling, picnicking and other reasons. Some bring dogs that can disturb nesting, which can cause nest failure. This impact is significant because of the breeding strategy of all terns.
They breed in colonies and on open ground, often near water. This is usually on gravel beaches, shell banks or flat sand. Their courtship is complex and includes aerial chases. The pair scrapes a shallow depression to lay two to three eggs. The shallow scrape is lined with grass, seaweed or moss. The eggs are 2.6 inches long with a pinkish-buff marked in brown. Both sexes incubate the eggs for 20 to 22 days.
The nestlings are semiprecocial, meaning they are mobile, remain at the nest and are fed. The nestlings fledge in 30 to 40 days. Young recognize the call of their parents. Parental care of the young is the longest among terns as the parents feed the young for five to seven months postfledging.
Since the Caspian tern nests on the ground close to water, it is vulnerable to unusually high tides, severe storms, terrestrial predators, vegetation invasion, chemical spills and human disturbance. Its limited breeding and roosting sites mean that any disturbance could have a severe impact on Florida’s Caspian tern population. Human disturbance during the breeding season poses one of the more serious threats to Florida’s Caspian terns.