Bowerbirds: New Guinea’s sexy Bob the builders

A glimpse into the mating behaviours of two of New Guinea's bowerbirds: Sericulus ardens and Amblyornis macgregoriae

Isabel Lamb
14th July 2020
The forests of the world are home to many species of bright, bedazzling, & bejewelled birds; the brightest of all possibly being the male flame bowerbird (Sericulus ardens).

Found in New Guinea’s rainforests, he sports a gradient of red, orange, and yellow feathers that cover his entire body and a tail tipped with black. He is named not only after his eye-catching plumage but also after his bower building tendencies. A bower is a structure of twigs and forest debris that a male will build in the hope of attracting a mate. Different from a nest as they are not used to lay eggs and raise newly hatched chicks in. The flame bowerbird’s bower is shaped like an upturned humpback bridge, which he will sometimes decorate with vivid objects he finds on the forest floor, such as blueberries or a variety of fallen feathers from other birds, just to add that little extra touch.

But he is not the only one to turn his claws to construction, the male Macgregor’s bowerbirds (Amblyornis macgregoriae) of New Guinea’s mountain forests also partake in this unusual behaviour. Macgregor’s bowerbirds are bland and brown, with an orange tuft of head feathers being their most colourful feature, but what they lack in appearance they make up for with their ability. Their bowers are towers of sticks, stacked like a game of Jenga, that can reach a few metres in height and take years to build. The tower is adorned in carefully placed plant debris and tree sap, similar to baubles on a Christmas tree.

Image: @Joses tirtabudi

Such behaviour may seem strange to an observer but the motives behind the behaviour are clear. All this effort is gone to, purely for the intent of attracting a mate. In a rainforest where sustenance is readily available and easily accessible, proving you are the best at gathering food may not be all that impressive to a female on the hunt for a mate with the best possible genes to pass on to her offspring. Therefore you might need to find alternative ways to show her why she should mate with you.

Unknown to these birds two types of sexual selection are taking place. Intrasexual selection that occurs when one sex (usually males) compete with one another for access to the other sex (usually females), and Intersexual selection that occurs when members of one sex (usually females) choose a mate based on certain, conspicuous characteristics.  

Female Macgregor’s will look for the tallest tower as the ability to build to great heights and maintain the height of your tower indicates good genetics; desirable to a female looking for the best genes and chance of survival for her offspring. The males will also compete amongst themselves to have the tallest, most enticing tower in the neighbourhood by sabotaging each other’s when they are left unattended.

But it is not as simple as just attracting a female to your bower, you must also woo her with a display that would put many a Broadway performance to shame. The flame bowerbird will coax a female into his bower by expanding and contracting the pupil of one of his yellow eyes. But he must be careful, to little or too much eye work and she will leave unimpressed.

The Macgregor’s bowerbird has a different trick up his feathery sleeve, he has the gift of mimicry. First, he must impress the female with his entire repertoire of sounds, which can include the songs of other birds, the noises of forest creatures, and even the chatter of children playing. Next, he plays a game of hide and seek around his bower, this keeps the female keen. Maybe she wants what she can’t have, or at least what she can’t see? Then he dances for her, puffing up his orange tuft so it looks like a dandelion, he moves one of his wings in slow, circular motions and shakes, and shimmies his body. Finally, if she is impressed, then he head butts her. How romantic! An odd routine that if dazzles her enough leads to success and the male bowerbird gets to mate.

Image: Joao Tzanno via Unsplash

This flashy behaviour that keeps a bird occupied could be said to be questionable in a place where predators are always lurking nearby. It's hard to hide if you’re the brightest bird in the forest or build a metre high tower which is equivalent to a sign that says, ‘Here is where I like to hang out’, or if you’re mimicking the sounds of their favourite meal. However the need to attract a mate and successfully reproduce seems to outweigh any concerns, and maybe surviving and thriving proves to the female that you can do so even with such impediments, perhaps providing her with even more reason to mate with you, therefore acquire the best genes for her offspring.

And the birds are not without some forms of defence. The Macgregor’s bowerbird can use its mimicry talents to imitate the sounds of its predator’s predators. As well as the sounds of wild dogs to scare away any wandering pigs that might accidentally knock over his tower in their search for buried treasure troves of food.

Bowerbirds are not the only ones to use colour, vibrancy, performance, and skill to attract a mate, these fascinating routines are happening all throughout the trees and floors of the world’s forests. But bowerbirds do it with such enthusiasm and attention to detail it is hard to not be impressed. Whether a performance ends in a successful mating or not (for some bowerbirds they will sadly never get the chance to mate) it cannot be said by anyone that male bowerbirds don’t put in the effort.

Featured Image: Crystal Mirallegro via Unsplash.

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