14-8-2017 AMSTERDAM ZOO, NETHERLANDS - INCA TERN (MALE) (Larosterna inca)

The Inca tern is one of the world’s most beautiful and interesting birds. It occurs along the Pacific Coast from northern Peru to central Chile. This bird is easily recognizable with its dark gray body, and red-orange beak and claws, and its lovely white moustache. It is an adept flier that swoops and hovers before it dives after its prey. It sometimes plucks pieces of fish out from between sea lions’ teeth. Unfortunately, their populations are declining quickly because of the loss of nesting sites. They have been included in the “close to vanishing species” category. Inca terns in the wild live up to 14 years and in captivity up to 20 years.

The Inca tern is a large tern, approximately 40 cm (16 in) long. Sexes are similar; the adult is mostly slate-grey with white restricted to the facial plumes and the trailing edges of the wings. The large bill and legs are dark red. Immature birds are purple-brown, and gradually develop the facial plumes.

The Inca tern is a diurnal, gregarious species, living and nesting in large colonies numbering several thousand birds, often close to gull colonies. Inca terns follow fishing boats and often associate with whales and sea lions when feeding, stealing food from these fellow marine mammals. Inca terns feed by plunge-diving from a height, after a brief flight above their prey, or by surface-dipping, whereby they swim or sit on the water and pick up prey from the surface. They are not strong swimmers, as their webbed feet are not big enough. Inca terns remain resident within their range, though non-breeding birds sometimes move, depending on food resources.

Inca terns are monogamous, pairs often returning to the same nesting site year on year. Courtship consists of an elaborate ritual, particularly for birds seeking their mate for the very first time. Males perform an agile flight display to impress their chosen female. They also perform courtship feeding while following the female while flying, with a fish in their bill. This species breeds twice a year, firstly between April and July, secondly between October and December. Nests are on guano islands or sandy beaches and they choose deep rock crevices where there are many cavities and cliffs that offer good protection. Chicks hatching in deep holes are given protection for longer from predators, whereas nests that are further from cliffs are more accessible to raptors and large seabirds. 1-3 eggs are laid and incubation lasts for about 3-4 weeks. The parents both incubate and feed the chicks. The young are grayish in color and fledge at about 4 weeks old. They reach their independence one month later and will be ready to breed at age 2 or 3.

Inca tern numbers are affected by food resources, as well as El Niño and other strong storms. Populations decline during such severe storms, though they fairly quickly become stable again. The biggest threat currently is over-fishing, as this reduces the fish available for the terns to eat. Production of guano can also reduce the number of nesting sites available, and cats and rats may eat eggs and chicks.

According to the IUCN Red List, the total Inca tern population size is more than 150,000 individuals. Currently this species is classified as Near Threatened (NT) and their numbers today are decreasing.