Malaysian Birds

Terns

Terns are long-lived birds that, by and large, enjoy a relative lack of natural predators and parasites. Unfortunately, most species are experiencing a decline in numbers, primarily due to human activities, including habitat loss, pollution, disturbances, and predation by introduced mammals. The Chinese crested tern, for instance, is in a critical situation, and three other species are classified as endangered.

In terms of size, terns exhibit considerable variation, ranging from the petite Least Tern, measuring 23 cm in length and weighing a mere 30 grams, to the larger Caspian Tern, with a length of 48 cm and a weight of 700 grams. Distinguished by their slender build, lighter bodies, and streamlined appearance, terns stand apart from gulls. The elongated tail and narrow wingspan contribute to their graceful flight.

Both male and female terns are identical in appearance, with males typically being two to five percent larger than females and sporting relatively longer bills. Sea terns often feature deeply forked tails or, at the very least, a shallow V shape. Noddies, on the other hand, typically have notched tails, with the longest tail feather located in the middle outer position, rather than at the center or outermost edge. Despite their short legs, terns are adept runners and rarely engage in swimming, typically landing on water only for bathing.

The majority of sea terns exhibit light gray or white body plumage as adults, complemented by a black cap on the head. The coloration of their legs and bills varies, encompassing combinations of red, orange, yellow, or black, depending on the species. The pale plumage serves as a conspicuous marker at sea, attracting other birds to productive feeding areas for various fish-eating species. Against the sky, the white underparts help conceal hunting birds from their prey. However, during the breeding season, certain terns, such as the Black Tern, White-winged Tern, and Black-bellied Tern, develop black underparts. Anous Noddies, in contrast, exhibit black plumage with a pale head cap. The evolutionary reason behind the dark plumage in these birds remains unknown, though it's been suggested that in tropical areas with limited food resources, less conspicuous coloration may make it harder for other noddies to detect a feeding bird.

The type of plumage, particularly the head pattern, is linked to the phylogeny of terns, with pale-capped, dark-bodied noddies believed to have diverged earlier than other genera from an ancestral white-headed gull.

Juvenile terns typically have brown or yellow-tinged underparts, featuring feathers with dark edges that create a plumage resembling scales. Dark bands on the wings and a short tail are also characteristic of juvenile terns in most species. The transition to adult plumage usually occurs after migration, with the bird gradually resembling an adult but retaining some juvenile features, such as a white forehead with only a partial dark cap. Full maturity is typically achieved by the third year.

After breeding, terns molt into a winter plumage, typically exhibiting a white forehead. Uncommon plumage variations, such as melanism and albinism, are much rarer in terns than in gulls.

Gulls