Migratory Bird Blog -
As spring draws to a close and seasons begin to turn…it’s time to welcome some of our favorite summer time visitors- the terns! Terns are a family of seabirds found worldwide that spend their lives near the sea, rivers, and wetlands. Terns can be seen throughout Southern California diving into the water, bill first to catch fish.
The Caspian Tern is the largest tern in the world, similar in size to a gull. This tern is easily identified by its large coral-red bill, black cap, and white body, and its tail is less forked than other terns. Adult birds have black legs, with pale grey upper wings and backs. You may see them soaring overhead, and catch a glimpse of their pale underwings and dark primary feathers. During winter months the black cap remains present, unlike other terns.
Caspian Terns have a very large distribution. They breed in North America, Europe, Asia, Africa, and Australasia. Caspian Terns breed in a variety of habitats along water, including salt marshes, barrier islands, dredge spoil islands, as well as freshwater lake and river islands. During non-breeding season, these terns reside in Old World tropics, Africa, and Australasia.
Caspian Terns have quite the maternal instinct, and will aggressively defend their breeding colonies. Adults will attack and pursue potential predatory birds and humans who invade their colonies. These birds build their nests in colonies on island beaches. Their nests are scrapes on the ground, lined with dried vegetation, pebbles, and sticks.
The Forster’s Tern is a medium-sized tern that looks similar to other terns. It can be identified by the comma-shaped black ear patch it sports in winter plumage. This bird is also white with a black cap, and it tail is long and deeply forked. This bird has white wings in most plumages, and its legs are orange and a little bit longer than others’.
This tern is the only tern that is restricted almost entirely to North America throughout the year.
Forster’s Tern breed in loose colonies and build a variety of nests. Some form unlined scrapes in mud or sand, others build an elaborate floating raft of vegetation, and some build nests on top of muskrat houses. Nests are typically built close to open water. Forster’s and Black terns breed near each other in marshes. Their precocious young wander and parents of each species have been seen feeding the other’s young.
Forster’s Tern will plunge-dive for fish, but will also catch insects in flight. These birds usually dive directly rather than hovering. During courtship, males offers females fish in an effort to gain a mate. After all, one good tern deserves another! Forster’s Terns can be seen frequenting the Colorado Lagoon throughout the summer and it is a spectacular place to watch courtship behaviors and plunge-diving!
The California least tern is a subspecies of Least Tern that breeds primarily in bays of the Pacific Ocean with a very limited range of Southern California, San Francisco Bay, and northern Mexico. This subspecies is the smallest of the American Least Tern, and has long narrow wings with a broad, forked tail. Like our other visiting terns, they have a black-capped head, black-tipped, pale gray wings and a white body. They also have black stripes running from the cap across the eyes to the beak, contrasting with a white forehead.
These birds visit us from April to September, when they head off for unknown destinations. During this time, birds court and nest on our beaches. Courtship is acrobatic, with males flying and calling with fish in their beaks. Receptive females give chase, and pairs weave into the air and then hurtle towards the ground in unison. On the ground, the male will approach with a fish, moving in a kind of dance. If the female accepts, they will mate. Nests are built in mid-May, and 2-3 eggs are laid. Both parents will take terns incubating the eggs for the 3 weeks until they hatch.
California Least Tern hunt in shallow water and will hover until they spot their prey. Once located, birds will plunge into the water without fully submerging. Here in Southern California, their favorite meals include anchovy, smelt, silversides, shiner surfperch, and small crustaceans.
Currently, the California Least Tern is listed as endangered, but hard work is being done to tern that around. One project is the Seal Beach Refuge, which has been built around the recovery of endangered birds such as the California Least Tern. California Least Tern recovery actions include nest site preparation, predator control, and monitoring. Volunteers are also used to monitor raptor distribution and movements around the Least Tern nesting colony on NASA Island.
To find out more about the recovery of these birds or the Seal Beach National Wildlife Refuge, visit http://www.fws.gov/refuges/profiles/index.cfm?id=81683
Tern fun facts!
· Terns used to be considered as a subfamily of gulls, but now are given full family status, Sternidae.
· Terns are normally monogamous, but trios and female-female pairings have been spotted in at least three species.
· The eyes of terns contains red oil droplets in the cones of their retinas. This oil improves visual contrast and sharpens distance vision, helping them locate shoals of fish. The red pigment also reduces UV sensitivity and damage.