Breeding ecology of Little Tern 1: Egg laying and hatching
The Little Tern (Sterna albifrons) is a small, slender and streamlined bird with a pair of narrow, sharp-pointed wings and forked tail (above). These adapt it well to a swift and graceful flight as well as plunge-diving for fish from a height above the water. The white belly helps to reduce its conspicuousness to underwater prey when the bird is flying over the water foraging.
As with most terns, there is courtship feeding when the male brings fish to feed the female. The pair may also indulge in aerial displays.
Once the pair has bonded and copulation occurs, the eggs are laid on a bare depression in the sand. A full clutch is three but usually only two eggs are laid (below). Both parents help in incubation and brooding. Whenever a parent bird arrives at the nest it will inspect the eggs and position them carefully before settling down to incubate them (below). Incubation usually lasts from 21 to 30 days. When hatched, the chick has its eyes closed (below left). The skin is clearly pink as the down feathers have yet to burst out of their sheaths. Within a few hours the chick dries up and begins to move about and by the next day it is totally covered with down feathers (below right). They are thus semi-precocial. The eggs are cryptic as they are thickly spotted with dark brown and pale lavender. However, with hatching the whitish inner surfaces of these egg shells can easily compromise the camouflage and attract the attention of predators. Thus they are removed as soon as possible and dumped some distance away (below).
Input and images by Dr Jonathan Cheah Weng Kwong.