(Host) Ruth Page describes forest families in which a single female mates with several males, and all the males care for the young.
(Page) There is at least one group of males in the world who are willing to share a single wife and devote most of their lives to protecting the young until adulthood, without knowing which of them is in fact the father. They’re birds, of course; and even among birds, they’re pretty strange. What they practice is called cooperative polyandry, and it’s essential for their race’s survival. Natural History magazine describes the life of the Amazonian white-winged trumpeter in some detail; it’s a unique story.
The mother bird’s nest is some 40 feet up in a tree, but the babies, just one day after hatching, toss themselves out of the nest and hit the ground with a loud thump. Instantly they’re surrounded by protective males, and after a bit of blinking and head-shaking, can move about. They’ll live on the ground for two years, fed and cared for by the males, some of them “teen-age” siblings, some of them – but who knows which? – fathers. With danger from boa constrictors, ocelots and jaguars, serious protection is essential. The watchful adults have a shrill warning call, part growl, part shriek, and form little phalanxes around any chick that is threatened.
The family is usually composed of one dominant male, two lesser males and a single female with whom all three can mate. A trumpeter group will also include relatives who are not yet sexually mature, but who help raise the babies, and an unrelated subordinate female who isn’t interested in child care.
Fruits of the fig tree are greedily gobbled by many forest creatures for whom they’re essential food; but inevitably some fall to the ground. The trumpeters feast on these, and helpfully disperse the tree’s seeds in their feces. The birds get 90 percent of their food from fallen fruit, and are among the few creatures for whom it’s the daily diet.
During the season when fruit is not available in one section of their huge territory, the birds have to remember where trees on a different fruiting schedule can be found. A single family group may have a territory of 175 acres, to assure adequate food. During the dry season, they survive with difficulty until the rains return. Any other trumpeters trying to move in are fought off. In one case an observer discovered an invader that actually succeeded in mating in another group’s territory; when it was discovered, the home group killed all the newly-hatched chicks.
These trumpeters reach sexual maturity at two years of age, and quickly depart. Females can have a tough time finding a group that will accept them, and wander from place to place until they find a group lacking a subordinate female. Eventually, the breeding female of that group may die or disappear, and the newcomer can take over the position. For traveling males, it’s easier; they are welcomed to mate with another group’s female, if they’re cautious; and can be counted on to care for chicks from then on.
This is Ruth Page describing one more delightful inhabitant of our planetary environment.