March 20, 2013 | 2
This move from my old site to the Scientific American network has also coincided with my own physical move from the UK to the USA to start some new research. Given this is the closing of a chapter of my life (or rather, my PhD thesis, which will now no doubt sit on a dusty shelf somewhere until a grad student picks it up in 10 years time to use as a door stop), I felt now might be an appropriate time to write a little bit about what I have been doing for the past three years. In the past I have only written about other people’s research, but given that I am now a few months beyond the shock (I will resist using the word ‘trauma’ here) of it ‘all being over’, I feel like it might be time now to share a bit of what I did over my PhD.
In one of my first meetings with my PhD supervisor, she said to me, ‘The way that I see it, you can either spend three months reading the limited amount of literature in your subject area, or you can go to Africa and get some data for yourself.’ This may have been the point where I realised I had chosen a good topic to study. Not only did not having much ‘literature’ to read due to the dearth of previous work done on this topic mean that I could kid myself that I was an ‘expert’ in the field after a few weeks, it was also liberating to know that most experiments that I carried out would be finding out new things.
So, even before moving my books into my new PhD office, I was on a plane to Botswana to collect data on the nest building behaviour of the Southern masked weaverbird. When I tell people that the aim of my research is to work out how birds learn how to build nests, I usually get one of two responses. The first is, ‘they don’t learn anything of course, nest building in birds is innate.’ The other response is ‘surely that’s been done already?’ But actually, both of these (perfectly reasonable) assumptions are incorrect.
There have been a handful of people who have tried to work out how birds build nests: Robert Hinde did a great set of experiments back in the 1960s with canaries, and got some feel for how these birds might be deciding how to choose material they build with. Then in the 1960s and 70s a couple (Elsie and Nicholas Collias) did a lifetime’s work with village weaverbirds and found strong evidence that this species do indeed learn many aspects of their nest building behaviour. However, despite this solid groundwork, hardly anything else was done to try and find out how birds build nests.
One of the first questions I asked when starting to think about this topic was whether birds might learn about building a nest from their own experience. The zebra finches I worked with were great for looking at nest building, as they would try and build with practically anything I’d put in the cage with them. Even if I didn’t want them to build, and so took what I thought was all possible building material from their cages, they would still pile up the kitty-litter pellets on the floor into a nest-shaped bulge to sit in. This ability of theirs to flexibly use whatever material was available was a useful feature that I exploited in my experiments with them. By giving pairs of birds a particular colour to nest with, I could see whether they then later preferred to build with this colour when building a second time.
Firstly, I gave pairs of zebra finches a choice between green and brown nesting material (dry hay dyed with food colouring), by giving them a small amount of each below their nest box. The males (who choose the material for building in this species) would then fly to either the green or the brown, take some to the nest, and then return to either colour and take some more. After they had made ten trips I took away all the material from them. I used these ten visits to tell which colour the males preferred. Almost all of them chose ten strands of a single colour, showing that their preference for one colour was strong (rather than say five of one and five of another). However, they did not all choose the same colour: most of the males preferred green, but some of them preferred brown. I then gave all the pairs of birds only one colour to build a full nest of: either the colour the male had preferred, or the colour he had not chosen (be it green or brown).
All the males seemingly happily built nests out of whichever colour I gave them, and the females then laid eggs and both partners incubated them. I wanted to see not only whether birds would prefer to build again with a colour they had previously built with, but also whether this was affected by the experience they had in the nest (i.e. a good experience where they fledged chicks from the nest, or a bad experience where they failed to reproduce). To address this, I let half of my birds (from each of the different treatment groups) fledge chicks from their coloured nests, but for half of them I took away their eggs after they laid them.
After the birds had either fledged chicks from their coloured nest, or had a ‘bad’ breeding experience where they had lost their eggs, I re-tested the males to see which colour of material they now preferred. I found that if a male built with the colour he had preferred to begin with (be it green or brown), he still preferred this colour, no matter whether he had had a good or bad breeding experience with it. However, if a male built with the colour he had not preferred to begin with, but then had a ‘good’ breeding experience with it where he built a nest and fledged chicks from it, he then preferred this colour after. On the other hand, if a male built using the colour he had not preferred to begin with, and then had lost his eggs from that nest, he continued not to like it.
Behaving this way might make sense in the wild, because if a bird chooses a material that leads to a bad breeding experience (for example, it doesn’t camouflage well, or doesn’t build a good structure), it might make sense for the bird not to choose it again in the future. On the other hand, if they find something that works, stick with it.
Although nest material colour is but a small facet of all the choices that go into building a nest, this experiment does show that there is some flexibility in nest building and that at least in zebra finches, males do change their decisions of what to build with based on their own personal experiences.
Collias, N. & Collias, E. 1984. Nest building and bird behavior, Princeton, Princeton University Press.
Hinde, R. & Matthews, L. H. 1958. The nest-building behaviour of domesticated canaries. Proceedings of the Zoological Society of London, 131, 1-48.
Hinde, R. & Steel, E. 1972. Reinforcing events in the integration of canary nest-building. Animal Behaviour, 20, 514-525.
Muth, F. & Healy, S. D. 2011. The role of adult experience in nest building in the zebra finch, Taeniopygia guttata. Animal Behaviour, 82, 185-189.
For more on bird nest building, see:
Secrets of the Universe: Past, Present, FutureX