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Black Tern

By Kathy Ross

Scanning the marshy flats of the Swan River Refuge in June, an ephemeral flash of luminous, sunlit wings catches the eye and intrigues the sense of wonder. Yes, it is live and it is a bird with a buoyant unique flight pattern of graceful swoops and aerial dives. As the light-colored wings turn away from the sunlight, the jet black head and body and silvery-grey, reflective wings of the breeding adult Black Tern contrast against a blue sky – a gift of the late spring migration.

The Black Tern, Chlidonias niger, like other tern species, is a member of the Laridea family, along with gulls. Terns in general tend to be smaller than gulls, with a sleek profile of pointed wings and pointed straight bills. The Black Tern is one of the smaller species, being around 10" long with a wingspan of 24 inches. Like gulls, terns have webbed feet and are colonial-nesting, water-loving birds with a wide range of habitats, from fresh-water marshes, prairie potholes, northern coastal shorelines to tropical beaches. While most gulls maintain fairly stable populations, tern populations in the northwest, including Montana, are on the decline. In general, tern individuals or small colonies may be found roosting on sandbars and shorelines amid flocks of gulls. I have often had summer sightings of one to five Black Terns on a particular log jam in the Flathead River, but having no sightings for the last two years has been disappointing.

The distinctive black head and body, fading to grey on the rump, easily distinguishes the Black Tern from other tern species, at least during the breeding season. The females are slightly duller black, but it takes a keen eye to discern between genders. Both have a very dark bill that is almost as long as the head. Midseason, when eggs begin to hatch, post-breeding molt begins and the characteristic black feathers begin to change. First, around the eyes white feathers appear. Whitening progresses from forehead to neck and eventually into the abdominal area. The molt is completed during fall migration. This basic or winter plumage then becomes pure white on the underside, except for small dark patches on each side of the breast. The back becomes a grey similar to wings and tail. At this time the juvenile’s plumage is similar to the adults except for a darker back, with wing coverts and cap that are barred and brown.

Often, vocalizations identify the Black Tern even before the silvery wings catch the eye. The shrill, metallic “kyew” can signal parents’ interaction at the nest and with young, foraging flights, and courtship flights. The “keek” call warns off enemies or threats to the nest. Both calls can have added syllables and variations depending on the intensity of the situation. It is well worth learning this call to experience these beautiful birds in flight or even be rewarded with the opportunity to see the nest with young.

The nests are generally built on floating mats of vegetation amid cattails, rushes, canary reed grass and other emergent vegetation. In Montana, besides recorded breeding in small ponds, marshes and prairie potholes, man-made islands and islands in man-made reservoirs are used as nest sites. The nests are loosely constructed out of old vegetation from around the nest site. Although in Montana little information is available on the reproductive cycle of Black Terns, it usually begins in early or mid-June. In general, ‘Black Terns are considered a single brood species’, laying 1-4 eggs of an olive-like color with dark markings, which hatch around 20 days after laying. (Later nesting has been known to occur if the first attempt fails.) The nest is aggressively defended by both male and female, who together share in the feeding and rearing of chicks. The young become mobile within days of hatching but typically do not fledge for 20 or so days.

Unlike many of the Laridea family species, Black Terns are not plunge-divers. They feed on insects caught on the fly and small fish or other aquatic prey skimmed off the water’s surface.

Little is known about Black Tern migration patterns through Montana, but observations have noted May and June for the spring migration and any time after July and as late as September for fall migration. They will winter along the gulf coasts, in the open ocean and as far south as northern South America.

This species is much on the decline across its historical breeding areas, including our regional and state populations. Many tern colonies vanished on the Atlantic coast by the end of the 19th century when hundreds of thousands were slaughtered for their feathers by the fashion industry. They are listed as threatened or endangered in many eastern states. In Montana, their numbers are very localized. The last two years have seen a decline in individuals as well as confirmed breeding sites. This decline may be due to human impacts such as habitat loss and pesticide use. Also, late season high water levels the last two years may have had impact on breeding.

* “Waterbirds will often move breeding colonies as wetland conditions change, making localized surveys of limited value without regional comparisons. Thus, participation in a region-wide colonial-nesting waterbird inventory may provide critical information for conservation of Montana’s waterbirds.” The Black Tern, along with a number of other waterbirds, is listed as a ‘species of concern’ by agencies such as BLM and Fish, Wildlife, and Parks. These agencies encourage volunteers. Become a Citizen Scientist and assist in keeping these beautiful terns part of our landscape! Participate in inventories and/or report any sightings of individuals or nesting activities to the above government agencies.

References:

The Sibley Guide to Bird Life and Behavior, by David Allen Sibley

Stokes Field Guide to Birds-Western Region, by Donald and Lillian Stokes

* “Mt. Colonial-nesting Waterbird Inventory – 2010 Report,” by Catherine Wightman and Fred Tilly

Websites:

Montana Fish, Wildlife and Parks

Montana Natural Heritage Program

Department of Environmental Conservation, New York State

Montana Field Guide

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