Recently I read David Haskell’s book ‘The Forest Unseen – a year’s watch in nature’. Haskell is a biologist living in Tennessee, and almost every day for a year he visited a single square metre of old-growth forest and described it in great detail as the weather and seasons changed. The book is beautifully written, almost poetically describing the interconnectedness of the ecosystem while capturing the scientific importance and wider implications of his observations.
I was inspired by Haskell’s book to pay more attention to my local environment and record some of my observations as I eat my lunch in the courtyard outside my building at the ANU Fenner School. We are so lucky in Canberra and particularly at the ANU to be surrounded by the bush and loads of wildlife, and as an aspiring ecologist I should really take advantage of the opportunity for some backyard observations.
Last week I was sitting on a bench reading a book, when I was distracted by a strange noise coming from the hawthorn tree behind me. I looked up and saw a pair of king parrots, quite a common sight at this time of year, feeding on the red hawthorn berries. But it wasn’t them making the weird noise.
It was a mechanical sound, buzzing and whirring like a wind-up toy. Then I caught sight of dark, glossy blue-black feathers and a purple eye – a satin bowerbird. His feathers were puffed up and he was flicking his wings in and out and bouncing up and down on the branch, quite a bizarre dance which I assumed must be part of his mating display – but where was the female? Sure enough, after a few minutes she flew down from a neighbouring tree and sat a few branches away from him. Unlike the male, her mottled green and brown feathers made her quite difficult to see amongst the autumn foliage, but her violet eyes were easy to pick out.
The male then ducked down to the ground and returned with something in his beak – which turned out on closer examination to be the yellow crest feather from a sulphur-crested cockatoo. The male continued his singing and dancing, trying to get closer to the female with his bright yellow offering. She kept her distance though, and eventually flew off after which the male gave up and disappeared into the thick bushes below the tree. I assumed that his bower must be there, so I looked underneath for his collection of blue treasures – but no such luck, although I did frighten a couple of rabbits (their numerous diggings were obvious in the litter and the nearby lawn).
Afterwards I thought that this behaviour seemed a little strange, so I did some research (as you do) and found out that bowerbirds are even more fascinating than I thought!
Firstly, the mating season is in summer, when the bowerbirds normally disappear from Canberra to breed in the wet forests to the west. Many Canberra birds to this, and return to the urban area in winter where there is more food. But it’s April, so why were they apparently mating now? The internet failed me on that question, so if anyone knows please leave a comment!
Secondly, why a yellow feather and not something blue? I always thought bowerbirds chose blue objects to decorate their bowers, but it turns out they also like yellow and often collect yellow leaves or fruits. Blue objects are less common though, so they are more impressive to the females.
Thirdly why were they up in a tree? Everything I have seen shows the female sitting in the bower itself, while the male dances and sings on the ground (see this youtube clip). While I was trying to find an answer to this question, I found an interesting paper in Nature by Seth Coleman et al. (2004), which looked at what drives female mate choice and how this affects the males’ displays. They found that younger females can be intimidated by intense male displays, so they base their choice mainly on the bower and decorations. Older females however can tolerate the most full-on song and dance, and males will often increase the intensity of their display to impress them. Coleman et al. hypothesised that the physical display is a better indication of mate quality because it can’t be faked, whereas the blue objects can be stolen from other bowers.
So perhaps this was an older, more experienced female who was more interested in the physical display than the bower itself…but it still seems odd that they were in a tree, away from the bower altogether. Any ideas please let me know!
Haskell, D. (2012) The Forest Unseen – A Year’s Watch in Nature. Viking, New York, USA.
Coleman, S. et al. (2004) Variable female preferences drive complex male displays. Nature, vol. 428 pp. 742-745