The Satin Bowerbird
Australia is home to ten species of bowerbird. Of these, perhaps the best known along most of the east coast of Australia is the Satin Bowerbird. On this page you can explore the amazing lives of these fascinating birds and the story of one of the most powerful evolutionary forces which has shaped their appearance and behaviour: sexual selection.
What is a bowerbird?
Bowerbirds are medium to large songbirds mostly famous for their elaborate courtship behaviour which generally includes some form of constructed “bower” along with a display of decorative items, dance, song and mimicry.
The various species of bowerbirds have a large distribution which reflects our ancient connection with Papua New Guinea and climatic changes which Australia has undergone across tens of millions of years. Thus bowerbirds can be found in habitats ranging from rainforest to woodlands to semi arid and arid shrublands.
Although it was thought in the past they are closely related to the Birds of Paradise, more recent analysis indicates that they’re more closely related to the treecreepers. This positions them closer to the lyrebirds in the family tree of birds and therefore among the most ancient of the world’s songbirds. Here we will only deal with the Australian bowerbirds.
There are three main groups of bowerbirds, those which construct an “avenue” of twigs which they decorate with various colourful objects, those which create elaborate, decorative arrangements or collections of plant material, usually around the base of a small sapling or stump. This is called a “maypole”. The third group, the catbirds (comprised of the Green Catbird, Spotted Catbird and Black-eared Catbird) creates no bower. There is a fourth, comprised of a single species, the Tooth-billed Bowerbird, the male of which clears a small court on the forest floor which he decorates with leaves to display with as he dances.
Satin Bowerbird identification
One of the best known bowerbirds of eastern Australia is the Satin Bowerbird. They can be found in tall wet forests, woodlands and even gardens on urban fringes throughout much of Victoria and the coast and ranges of much of New South Wales and Queensland. A population also exists in north Queensland, this seperate subspecies is a little smaller than its more widely distributed sister species.
Satin Bowerbirds can be mistaken for a crow or raven as they fly rapidly and directly through their forest or woodland homes. However, on a closer examination they are very different. The males are very flashy. Their plumage appears to be black until the light strikes them, revealing the gorgeous deep satin blue for which they are named. They have a chunky bone-coloured bill and a captivating bright purple eye.
The female Satin Bowerbird is a mixture of browns, creams and greens in various streaks on the upper body and breast and chevron shapes along her flanks and belly. Her equally chunky bill is quite dark. Immature males look very similar to the females though their bill will appear light after the first six to twelve months. They will not acquire the uniform satin black plumage of the adults for seven years.
Satin Bowerbird courtship and display
Young male Satin Bowerbirds can sometimes be found in small groups, building a simple “practice” bower where they will practice their decorating and courtship skills. However, they will all visit the bower of the local “maestro”, the adult males to observe more closely the intricacies of bower construction, decoration, dance, mimicry and showing off in general. Here they will find the adults create first a mat of small twigs upon which they will create a beautifully formed pair of walls, thick at the base and curving elegantly upward to comprise the “avenue”. They will decorate this with various blue objects. Before human occupation these would have been berries and the blue primary wing feathers and tail feathers of the Crimson Rosella (which are still commonly used today). Since the coming of Europeans they have taken to using discarded or stolen blue objects of human manufacture. They also use use yellow flowers and the crest feathers of Sulphur-crested Cockatoos, as well as shiny objects like snail shells and sometimes metallic objects.
The Satin Bowerbird is polygynous, meaning that the male will mate with many females but plays no part in the raising of their young. He devotes all his energy to pleasing the local female bowerbirds and she devotes all her energy to finding the right male, producing eggs and raising her young. The males will build their bower in a slightly open area where the sun can shine into it during the critical hours when they like to display. The site should have a tree nearby where the male can sit and call in a somewhat raucous, raspy fashion to attract a female. When she turns up he will fly down to his bower, call her over and she will stand at one end and sometimes in the bower avenue whilst he proceeds to show off. This will include repetitive dance steps, waving his favourite blue items for her to inspect, flashing his eyes as he dilates his pupils and sometimes perform mimicry. If the female is impressed, they will mate, she will depart and lay up to three eggs, two days apart, and raise the young entirely on her own. He will return to the top of the tree and commence to call the next female. She may visit several males before choosing.
The level of competition is very high among the males and it is common practice for them to visit the bowers of other males when they are unattended. They will proceed to smash them up and steal their decorations. It’s not sure how much value there is to this behaviour ultimately, as it is generally the case that few or even only one male in a given locality will be successful and he will sire all the young. The other males may never be successful.
When breeding season is over the females tend to gather in considerable numbers, sometimes with the younger males too. They will forage for fruit and invertebrates together until the weather begins to warm again. The older males tend to spend this time in solitude and will often seek out orchards and gardens on urban fringes where food is plentiful.
The Power of Sexual Selection
What drives the bowerbirds to adopt this odd lifestyle and extremely complex behaviour? Wouldn’t it be easier for the male and female to just find a mate to stay with and then help each other raise their young? The answer to this lies back to around 15 million years ago, back to the dawn of the bowerbirds.
Scientists studying the genetics and ancestry of bowerbirds have come up with two possible scenarios, that the bowerbird groups who create maypoles and avenues independently evolved this behaviour or that one group evolved this behaviour but through hybridisation. By this they mean that a species from a group of bowerbirds which evolved the behaviour of creating bowers bred with a bowerbird from the group which wasn’t. Their offspring retained the drive to produce bowers too and gradually as the genes from the hybrid bird moved through the population this became the common practice throughout that species.
However, the initial drive of the male birds to go through so much labour and so much seemingly odd behaviour is driven by the choices of the females. This is because ultimately, it is the female who will choose which male will mate with her.
In most instances female birds choose a male who will be able to provide well for her young, help feed her whilst she is brooding eggs, defend their territory and perhaps help build the nest too. In this way, strong males are usually selected and this ensures that she produces more offspring, whilst weaker males tend to be less successful. This helps keep the population viable, as the genes of the stronger birds will be more common. Even in this scenario, the female is looking for appearance and behaviour which indicates that the male is strong, healthy and on his best behaviour. This is called “fitness”.
Among the bowerbirds who went down the road of building bowers it seems that the females have been particularly fussy, constantly looking for that “something extra”, something which demands that the male have a strong constitution, not to produce elaborate plumage or to find food for her, which is common among many bird species. It seems that the female bowerbirds have acquired the behaviour of demanding that the males have the energy to create and elaborately decorate a complex construction upon which to display a dance which is just so and also produce the right vocalisations and mimicry.
As each generation keeps selecting along increasingly demanding lines, gradually the new sought after behaviour – the successful behaviour – becomes more widespread in populations and bowers along with their decorations and the behaviour of the males has come to resemble what we have today. This process is ongoing and in thousands of years to come the bowerbirds will possibly become even more elaborate in these things.
Humans are not immune from this behaviour, however it cuts across both sexes as we are a highly complex, intelligent and communal species. If we examine human (and other great ape) societies we can often see the behaviour of males and females tending to be styled to attract the opposite sex. Whilst females tend to advertise fertility, males tend to behaviours which demonstrate the capacity to provide and protect (much like so many male birds) . . . think of the red sports car or an expensive gold chain: frivolous but expensive trinkets which demonstrate to females that the owner can obtain excess abundance which could be used to support her and her children. These trinkets also demoralise the males which can’t acquire them, thus reducing competition.
Aussie Wild acknowledges the traditional custodians of the land which we visit, the Dharawal and Darug people. We pay our respect to their elders past, present and emerging.