Black Tern

New York Status: Endangered
Federal Status: Not listed

Description

The black tern is a small member of the Laridae family at approximately 10 inches in length and 1.75-2 ounces in weight. It is identifiable in the breeding season by its jet black feathers on the head and body, the back fading to gray on the rump. The bill is nearly as long as the head and is bluish with a trace of dark red at the gape; the feet are also dark red. The upper wings and tail are uniformly gray, aside from white lesser wing coverts which form a small white shoulder when the bird is at rest. During the winter, black feathers fade to gray on the back and turn white on the underparts. Juvenile black terns are similar to the adult in winter plumage, but have barred wing coverts and are generally scalloped brown overall. The call of this bird is a shrill, metallic "krik."

Life History

In early May, black terns return to New York from the wintering range and begin their courtship displays at communal feeding and resting areas. Mating pairs are established by mid to late May when they disperse to nesting areas in typically large (≥ 49 acres) "hemi-marshes" (50/50 ratio of open water to emergent vegetation). Nest-site selection and building is rapid. In approximately four days, black terns build shallow, cup-like nests upon floating substrates of matted, dead marsh vegetation, old muskrat houses, cattail rootstalks, emergent vegetation mats of algae, or fallen logs.

The single brood consists of 2-4 eggs. Both parents attend the nest and continually add nesting materials during the incubation period of 21 days. The chicks are able to swim, walk and run within two days of hatching and they fledge in 21-24 days.

Distribution and Habitat

The black tern is a semi-colonial waterbird that nests on inland marsh complexes, ponds, mouths of rivers and shores of large lakes. In North America, the breeding range extends from Central British Columbia, east across the prairie provinces to Central Ontario and Southern Quebec, and south to Central California, Utah, Wyoming, Kansas, Iowa, Illinois, Indiana, Ohio, Northern New York, and Northern New England. The black tern winters in marine and coastal areas of Central America and Northern South America.

In New York, black tern breeding colonies once occurred at 56 sites along the southern and eastern shores of Lake Ontario from Niagara Falls to Watertown, in marshes along the St. Lawrence River and inland marshes of Western, Central and Northwestern New York. Today, approximately 200 nesting pairs occur at less than 20 of the historic breeding sites.

Status

Beginning in the 1960s, the black tern population declined across its range. In the 1960s, a series of dams in the St. Lawrence River were erected to generate hydropower, stabilize Lake Ontario water levels for commercial shipping, and protect shoreline real estate from flooding. These dams limited the annual fluctuation of water levels that promoted the hemi-marsh conditions favored by nesting black terns, and resulted in a loss of breeding habitat.

Regular monitoring revealed that the number of colonial nesting sites in New York State decreased between 1989 and 2004 by 57%. This is primarily attributed to habitat degradation. The 2000-2005 NYS Breeding Bird Atlas data showed 40% fewer black tern-occupied blocks than the 1980-1985 Breeding Bird Atlas. Black tern nesting habitat may be further compromised by agricultural run-off, pollution, invasive species, reduced invertebrate prey biomass, residential and commercial development, and recreational watercraft disturbance.

Management and Research Needs

Black tern surveys are conducted every three to four years by New York State Department of Environmental Conservation staff and volunteers at historical and current nesting sites. These surveys are a critical component to monitoring the status of this declining species, and are necessary to identify factors that will improve conservation efforts and restoration of nesting sites.

Currently, invasive species control and water level manipulations are the most effective strategies of black tern habitat management; however, both can be costly and time and labor intensive. In New York, the impact of agricultural run-off and pesticide contamination has been suggested as a compounding factor to habitat loss. Additional research focused on habitat quality, water quality, and prey populations is needed to determine the impact of habitat degradation on black tern diet and nutrition, which may be limiting successful breeding.