COOPERATIVELY SINGING MELODIOUS BLACKBIRDS

Melodious Blackbirds are common from central Mexico to Costa Rica. We have lots of them at the hacienda. They are like the US's Red-winged Blackbirds except that they are totally black. You can see one at http://world.std.com/~eva/belize/Cockscomb/bze_melodious_blackbird.jpg.

I'm astonished that my field guides do not mention something remarkable I am seeing these birds do every morning: They are "cooperatively singing." Two birds cooperate in making a call that sounds like it is coming from a single bird.

The songs are very varied but a classic case arises when two birds are perching together high in a tree preening as the rising sun warms them up. One bird suddenly makes itself taller and stands stiffly, enlarges his chest and ruffles his feathers, and opens his beak.

His companion, seeing these signs, does the same. Then follows a two-bird-made song in which one bird makes a piercing POING call, which can sound a little like a much amplified drop of water in a bathroom sink.Another part of the call is a loud CHRRR or maybe a metalic-sounding ping, which may begin the call. The two birds alternate their calls for several seconds and it sounds exactly as if one bird were making a single very melodious call. As the birds call they pump up and down on their legs, alternating with one another.

Sometimes the cooperating birds can be 50 or more feet apart, in different trees, but then the complementary effect is not nearly as coordinated. The calls are usually out of phase and often the birds don't bother to pump their legs with such vigor. They need to be about two feet apart to really do a good job. Often, especially later in the day, birds sing alone, performing just one part of the song, and sometimes lone birds call with other sounds not incorporated in the POING CHRRR or PING POING call. Lone birds don't seem nearly as enthusiastic about their calling as birds in a pair cooperatively singing.

Apparently these callings are at least partly meant to defend territory, because when a couple nearby calls I can hear far away another couple responding.