Beta bower birds bonk by beating bullies
Iconic Australian birds show innovative ways of competing against alpha males. Andrew Masterson reports.
It is rarely advisable to anthropomorphise the behaviour of non-human animals, but in the case of socially dominant male great bower birds (Ptilonorhynchus nuchalis) it seems appropriate to describe them as bullies, vandals and thieves.
The species is one of 20 Australian bowerbirds, all deeply loved by ornithologists and bird fans because of the habit among males of building elaborate courtship arenas, called bowers, surrounded by a curtain or avenue of twigs and decorated with collected colourful objects.
The great bower bird, which is common in the north of the continent, builds a bower about one metre long and 45 centimetres high, usually beneath a shrub. It has a preference for green and white decorations, dotting the structure with leaves, stones, shells and, if available, bottle tops and pieces of glass.
So far, so charming. However, research published in the journal EMU: Austral Ornithology reveals that socially dominant, or “alpha”, male bower birds go out of their way to destroy the bowers of their weaker “beta” rivals, and to steal all the pretty things the young males have painstakingly gathered.
Zoologist and author Natalie Doerr, of James Cook University in Townsville, Australia, reveals that the beta males are not the sort of birds to slink away in defeat. Far from it.
During her fieldwork, Doerr discovered that socially inferior males denied the opportunity to use an elaborately constructed bower as a backdrop for mating behaviour opt instead to use a tree trunk. Tree trunks, it need hardly be pointed out, cannot be destroyed by even the most aggressive alpha bloke.
In studying the behaviour of these beta males – who are trying to increase the odds of passing on their genes – Doerr noted that the choice of display tree was not random.
Rather, the birds appeared to select trees with trunks roughly the same width as a bower, allowing thus the same sort of displays. Proper bowers tend to be built roughly equidistant from each other across a population range, but the display trees were usually positioned conspicuously close to real big boy arenas – a strategy, Doerr suggests, allowing “younger and less competitive males to attempt to attract females visiting nearby”.
Cheeky little sods.