Caspian Terns are the only large terns likely to be seen on inland waters, including within South Dakota. Less sociable than many terns, they are often seen singly or in small groups. Known for their aggressive feeding tactics, Caspian Terns won't hesitate to steal a catch from another bird, or raid a nesting colony for eggs and young birds. Young of the species are dependent upon their parents for a much longer period of time than most other terns and gulls, and can still be seen begging parents for food in mid-winter.
Habitat
The Caspian Tern inhabits a wide variety of aquatic environments including large lakes, reservoirs, rivers, marshes, estuaries, coastal bays, beaches, and ocean shorelines. It nests on sandy islands, gravel bars, dredge spoil islands, and other open sites near water where vegetation is sparse and visibility is good. During migration and winter, it frequents both inland and coastal waters wherever fish are abundant.
Diet
Primarily feeds on fish. They often focus on just one or two primary prey species, which vary from location to location. They will also feed on large insects, eggs and young birds, and occasionally crustaceans or mollusks.
Behavior
The Caspian Tern is a powerful flyer that often patrols over open water searching for fish. It typically hunts by hovering briefly and then making a steep plunge-dive to capture prey near the surface. Caspian Terns are often seen singly or in small groups while foraging, but they nest colonially on islands and sandbars, where they vigorously defend nesting territories. Their slow, deliberate wingbeats and large size give them a distinctive gull-like appearance in flight. Very aggressive, they will often steal food from other bird species.
Nesting
June and July. The nest of a Caspian Tern is a shallow depression on the ground, sometimes lined with bits of vegetation or debris. The female usually lays between 1 and 3 eggs, and both parents help to incubate them. When the eggs hatch, both parents help to feed the y oung. Young fledge after about a month, but typically stay with the parents for several months after fledging.
Song
The Caspian Tern gives loud, harsh, gull-like calls often rendered as kerr-ack. These deep, raspy vocalizations are frequently heard around nesting colonies and while birds are flying overhead, making the species easy to detect even at a distance.
Migration
Summers along coastlines and in widely scattered inland locations throughout Canada and the United States. Inland birds move to coastlines in the winter, and wintering birds can be found southward through northern South America.
Similar Species
In South Dakota, somewhat similar to Common Tern and Forster's Tern. The Caspian Tern is much larger and heavier-bodied than both the Common Tern and Forster's Tern. It has a massive, thick bright-red bill, a broad chest, and slower, more deliberate wingbeats that often make it resemble a small gull in flight.
The Common Tern is noticeably slimmer, with a much smaller red-and-black bill, a more buoyant flight style, and a deeply forked tail. Forster's Tern is also much smaller and more delicate, with a longer tail, a thinner orange bill, and paler silvery-gray upperparts.
In nonbreeding plumage, Caspian Terns retain their large size and thick bill, making identification straightforward. Their voice is also distinctive—a deep, harsh, rasping “kraaah” that is much lower-pitched and rougher than the sharper, higher calls of Common and Forster's Terns.
Conservation Status
The Caspian Tern is generally considered a species of low conservation concern globally because of its wide distribution across multiple continents. However, some regional populations are vulnerable to disturbance at nesting colonies, loss of suitable island nesting habitat, changes in water levels, pollution, and declines in fish populations. Conservation efforts often focus on protecting breeding colonies from human disturbance and maintaining suitable nesting islands and shoreline habitats. The IUCN lists the Caspian Tern as a species of "Least Concern".
Photo Information
February 13th, 2008 - Bon Secour National Wildlife Refuge, Alabama - Terry Sohl
Interactive eBird Map
Click to access the interactive eBird species sightings page for Caspian Tern
