Male bowerbirds use forced perspective to win a mate
Some male bowerbirds lay out objects in front of their bower from smallest to largest. Seen from where a visiting female stands, the arrangement creates an optical illusion that keeps her looking longer, and males with stronger illusions tend to mate more often. Architecture, decoration and stagecraft all go into the pitch.
The family has 23 species living in New Guinea and Australia, from the golden bowerbird at 22 centimetres to the great bowerbird at 40. Their name comes from the courtship structures males build. Some raise maypole bowers by stacking sticks around a sapling, a few adding a hut-like roof; others make avenues between two walls of upright sticks. The male then decorates the site with brightly coloured objects.
Females shop around. They visit several bowers, return to favourites, watch the displays and inspect the construction, narrowing their options until many choose the same male and plenty of poor performers get nothing. Males seem to adjust their routine to how a female responds. Because the male gives no parental care, researchers suspect females gain genetic benefits, but that is hard to prove when males take seven years to mature.
Many are superb vocal mimics. MacGregor's bowerbird has been heard imitating pigs, waterfalls and human chatter, and satin bowerbirds work other local birds' songs into their courtship. Such behaviour has led some researchers to rank bowerbirds among the most behaviourally complex birds, and Darwin wrote about them alongside birds-of-paradise. One idea holds that decoration shifted from plumage to bower so bright males would be less visible to predators, though similar-looking species build very different bowers.
Catbirds, named for their meowing calls, are the exception: they build no bower, pair for life and share chick-rearing. In every other species the female builds the nest and raises the young alone. Eggs are unusually heavy, roughly twice the norm for a songbird of similar size, and bowerbirds live long for passerines; one satin bowerbird reached twenty-six years, beyond any recorded raven.
Source: Bowerbird
