Introduction

The Black Tern differs from other North American terns in several respects. It is small, has a black head and underparts in breeding plumage, eats insects as well as fish, and nests in freshwater habitats. This bird is described well by Bent (1921: 297) as “a restless waif of the air, flitting about hither and thither with a wayward, desultory flight, light and buoyant as a butterfly. Its darting zigzag flight as it mounts into the air to chase a fluttering moth is suggest[ive] of a flycatcher or a nighthawk; as it skims swiftly over the surface of the water it reminds me of a swallow; and its true relationship to the terns is shown as it hovers along over the billowing tops of a great sea of tall waving grass, dipping down occasionally to snatch an insect from the slender, swaying tops.”

The Black Tern nests semicolonially amidst emergent vegetation in biologically rich wetlands. Nests are flimsy, often floating, and are easily destroyed by wind or changing water levels. Reproductive success varies greatly. Adaptations to marsh nesting include frequent renesting, low site tenacity, and eggshell morphology suited to damp conditions.

This highly social species often forages in flocks. It migrates through the United States, then shifts to primarily marine habitats in winter. There it favors productive marine waters, especially off the Pacific Coast of Panama, and often concentrates where predatory fish have driven small prey to the surface.

Populations of this tern in North America and Europe have declined markedly, at least since the 1960s. Loss of wetlands on breeding grounds and migration routes is probably a major cause, but food supplies may have been reduced through agricultural control of insects and overfishing in the marine winter range.

This account deals almost entirely with the North America subspecies of Black Tern (C. n. surinamensis). For details on this species in Europe (C. n. niger), see Cramp (1985).