Thursday, 13 July 2017

Bowerbirds; charismatic old Australians

Bowerbirds have long fascinated laypeople and scientists (not to mention the odd natural history blogger). Obviously enough the key focus has been on the remarkable behaviour which gave them their name - the males' extraordinarily complex display stage and performance - and I shall be taking up that theme here.
Great Bowerbird Chlamydera nuchalis at bower, Boodjamulla NP, Queensland.
Their very origin and nature has been long debated, but it seems the answer is more interesting, and perhaps surprising, than the position held until recently that they are very close to the birds of paradise. In fact they are not close at all to those other great displayers; there are three Australian super-families of the old Gondwanan passerines, and the bowerbirds belong to the oldest of them (Menuroidea), along with lyrebirds, scrubbirds and treecreepers. (Birds of paradise, in the super-family Corvoidea, are closest to the White-winged Chough and Apostlebird, monarch flycatchers, and crows and ravens.)

There are 20 species, 10 restricted to New Guinea, eight to Australia, and two shared. Most are tropical, suggesting that their origins lie there, though one has expanded well into the temperate south-east. Two in Australia are at home in semi-arid and even arid inland woodlands. All are primarily fruit-eaters, and most also eat leaves, unusually among birds (especially in Australia); invertebrates, and even frogs and small lizards are also widely taken, especially for feeding to chicks.

Building the bower is a huge undertaking. Firstly a platform is created, comprising a deep layer of sticks, into which curved sticks are inserted, facing inward to form an avenue. In a series of Great Bowerbird bowers in Queensland, between 1400 and 1800 substantial sticks were counted in the bower (not counting the platform). Decorations vary between species, but while the Satin Bowerbird of the east coast of Australia does use primarily blue items to reflect his own colour, others tend to use a range of paler objects.
Satin Bowerbird bower, Bomaderry Creek Regional Reserve, suburban Nowra.
Here the blue decorations are almost exclusively artificial - plastic straws above,
and milk bottle rings below. (Sadly the latter have proved fatal in some cases, getting caught around the bird's neck.)
In more natural situations I have seen blue feathers, flowers and berries, and more unusual
items (which are apparently highly sought) such as shed snake skins and bones.
The Great Bowerbird bower at Boodjamulla featured many stones, some bones, plastic,
green berries and beer can ring-pulls...
... while this one south of Darwin focussed almost entirely on big snail shells...

... and this one in the same area was captivated by green bottle glass.
This Western Bowerbird bower (note that unlike the previous species, this one is open at the top)
at the Olive Pink Botanic Gardens in Alice Springs, central Australia, had a more modest collection
of bones and white plastic...
.... while this one nearby was taken by the fruits of Quandong Santalum acuminatum.
Most species paint the inner walls of the bower with a 'brush' of bark, using charcoal and chewed-up leaves and fruits. The bower is aligned north-south to make the most of the light on the decorations.

In Australia all but one of the bower-builders construct these avenues; only the Golden Bowerbird of the ranges near Cairns in north Queensland belongs to the 'maypole bower' school of construction. In this group, sticks or orchid stems are piled up around a sapling, or pair of saplings, to two metres high, and decorated with lichens and white flowers and fruit.
Golden Bowerbird bower, Mount Elliott, north Queensland.
(Scan of old slide - sorry.)
There is a high level of aggressive competition between males, with constant theft of desirable decorations, and damage to the rival's bower, to put him out of the contest for a while. And it is a bitter contest, with the less successful males not mating at all. 

Some of the plainer species have a brilliant pink or lilac erectile crest, which is normally hidden in the plumage of the crown. 
Western Bowerbird Chlamydera guttata, Olive Pink Botanic Gardens in Alice Springs, central Australia.
This is the most arid-loving bowerbird, found in the central and western deserts.
It seems that the quality of the bower really is telling her something about the quality of its owner. Perhaps surprisingly, a study on Satin Bowerbirds found a high correlation between the quality of the bower (using four defined features) and his health with regard to external parasites, plus his size. They also found that a more intense body colour (measured by reflectance spectrometry) was a predictor of low internal parasite loads and healthy feather growth rate, as well as body size again.
Satin Bowerbird male, National Botanic Gardens, Canberra.
The display is frenetic and riveting. In the case of the Satin Bowerbird he goes into a trance-like frenzy of display, his violet eyes bulging, his necked arched and wings alternately flicking rapidly and held stiffly above his back. With a favoured item from the display platform in his beak, he lowers his bill and raises his tail, standing on tip toes, all the while buzzing and clicking more like a machine than a bird. After some time of this he suddenly goes quiet, stepping partly out of sight behind the walls of the bower, showing her just his head and the object. At this stage he often erupts into virtuosic mimicry of other birds.

There is a long apprenticeship to get to this level of panache. In the Satin Bowerbird, and others, it takes six years for a male to attain his adult plumage; until then he resembles the females, and builds scores of bowers, probably all of which will be destroyed by his peers and elders.
Female or immature male Satin Bowerbirds, Canberra.
Sixteen of the 20 species build a bower; the three more primitive catbirds do not do so, but form monogamous pairs for breeding. The Tooth-billed Bowerbird Scenopoeetes dentirostris of the Queensland Wet Tropics uses a cleared display area, but does not construct.
Spotted Catbird Ailuroedus maculosus, Millaa Millaa Falls, north Queensland.
This primitive rainforest bowerbird is one of the two bowerbird species found in both Australia and New Guinea.
The name comes from the hair-raising yowling calls, which can also sound disturbingly like
a human baby crying.
The bower-builders are exclusively polygynous, with a male attempting to lure as many females as possible by his bower and accompanying display. Should she be impressed she enters the bower or mounts the platform and mating takes place there. From then on she's on her own; she's already built her nest and all brooding and chick-raising is down to her. 

Let's just end with a few bowerbird portraits, including a couple I've not yet illustrated.
Great Bowerbird, Croydon, north Queensland.
There can be something slightly unsettling about the intensity of scrutiny applied by this bird,
the largest of the bowerbirds.
Green Catbird Ailuroedus crassirostris (in the rain), Bangalee, near Nowra, New South Wales.
This, the second Australian catbird, is found well to the south of the range of the tropical Spotted Catbird.
Spotted Bowerbird Chlamydera maculata, Bladensburg NP, central Queensland.
This beautifully patterned bird is one of the two inland species.
Western Bowerbirds, Olive Pink Botanic Gardens.
Once lumped with the Spotted Bowerbird, it is a more richly coloured bird and found to the west.
Bowerbirds, a special part of Australia.

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KayePea said...

An nteresting post thanks Ian, and love all the photos.

Ian Fraser said...

Thanks KayePea, and good to hear from you as ever!