Boat-billed heron

The boat-billed heron (Cochlearius cochlearius) is the only member of the Cochlearius genus within the Tigrisomatinae subfamily of herons (Ardeidae). It has proved difficult to classify due to having features that seem to set it apart from other herons.

The boat-billed heron, otherwise known simply as the boatbill, inhabits freshwater mangrove swamps in Central and South America, anywhere from Mexico to Peru and southern Brazil. It is largely nocturnal, spending the daytime hidden in the mangrove thickets. It is therefore rarely seen and not everything is known about its habits.


Appearance

It measures about 22 inches in length, being mostly grey above and brownish below. It has black patches on its head, flanks and back and broad black crest feathers. The face and throat are white and the wings are pale grey.

However, the most unusual feature of the boat-billed heron is, not surprisingly, its bill, which is broad and scoop-shaped, three inches long and two inches wide. This is associated with a wide mouth, which in turn makes the head broad and the eyes, which are large to aid night vision, set wide apart. The boat-billed heron shares these features with no other heron, which is why its classification has been problematic.


Behaviour and feeding

Because it is nocturnal, and inhabits remote areas, observations of the boat-billed heron when feeding have been few and far between, so there is some speculation as to what advantage the birds gain from having such a strange-shaped bill. It is reported that its diet consists of worms, crustaceans, fish, amphibians, water snakes and small mammals such as mice. However, it is not clear how its bill would be useful for catching fast-moving prey such as fish or mice, as it would seem to be more fitting for sifting the mud of the mangrove swamps for worm and insects.

The boat-billed heron has a harsh frog-like croak and a high-pitched whistle. It also claps and rattles its bill, as some storks do.


Breeding

Pairs of boat-billed herons sometimes nest alone and sometimes in small colonies, occasionally alongside night herons. Pairs form after a mating ritual that involves the male bird displaying its crest feathers and offering sticks to the female. Both birds clatter their bills a lot at such times. Pair bonds are reinforced with mutual preening.

The nest is a shallow construction of sticks in a mangrove tree. Three or four blue-white eggs are laid, these being incubated by both partners, who also share in feeding the chicks, which hatch after about 25 days. The young birds stay at the nest for up to eight weeks.

© John Welford