Thursday, February 24, 2011

One of the most interesting and frustrating families we encountered in Costa Rica were the Antbirds. Antbirds are a large family of passerines, found across sub-tropical and tropical Central and South America. Over 200 Antbirds are known, of which 22 occur in Costa Rica.

We managed to spot eight of them, though their skulky habits in the dark understory made them quite a challenge. Trying to follow an Antbird sp. through the dark twiggy undergrowth required patience...

A male Barred Antshrike (c) Richard Brown

...but it was well worth it when one of these popped up into a clearing, however brief!

Barred Antshrikes were by far one of the most common Antbirds we encountered on our trip. They are rather widespread, occurring from Mexico through Central America, and into a large part of South America east of the Andes to Argentina, Bolivia and Paraguay. Because of this many sub-species are recognised. This male is of the intermedius race, the only race recognised in Central America.

Antbirds are so called because they have a habit of following ant trails, with arthropods forming the bulk of their diet. But Barred Antshrikes also take seeds and small fruits using their heavy, hooked bills.

The literature describes the Barred Antshrike as ponderous, but this one must have done most of his pondering in private because he didn't stay in one spot for longer than a few seconds.

The Barred Antshrike is sexually dimorphic, the females being rufous-chestnut with a barred head and throat. Both birds are rather cryptic, and perfectly camouflaged in the scrubby understory. This is important, because they share incubation duties. Sexual dimorphism is unusual in birds that share such duties, but it is thought that the male maintains his striking black and white barring in order to defend his territory and attract a mate. Once he has attracted a mate, the monogamous pair will mate for life.

Another fascinating fact about this species, and indeed Antbirds as a whole, is their breeding ecology. Only two eggs are ever laid, and while the parents share the tasks of incubation and feeding of chicks, once the chicks fledge, each parent cares exclusively for one of the chicks. Fantastic! Presumably, this ensures each chick is well fed, increasing the chances of survival.

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