A historical perspective
“It is a somewhat remarkable fact that not withstanding the extreme popularity of the subject of Birds’ Nests, no book has yet been published entirely devoted to these beautiful and curious objects. And yet their study — the science of Caliology — is one of the most fascinating branches of Ornithology, perhaps more intimately connected with those difficult problems and questions relating to the mental attributes of what man in his ignorance is pleased to consider the ” lower animals,” than any other. Indeed, there are many of us who would fain deny the existence of any reasoning faculties whatever in birds, classing their expression in a thousand different ways, all under the vague, meaningless and ridiculous term “Instinct.”
A bird’s nest is the most graphic mirror of a bird’s mind. It is the most palpable example of those reasoning, thinking qualities with which these creatures are unquestionably very highly endowed.
Evidence of this reasoning power confronts the student of Birds’ Nests as he gazes upon each procreant cradle, no matter how crude on the one hand, or how elaborate on the other…”
The role of cognition
Building a nest to hatch its eggs and raise its young in is probably one of the most important things a bird will do in its life time. The choices it makes about what sort of nest to build and what material to build it with will have a significant impact on the success of a nesting attempt. Despite some evidence that some learning is involved in such choices, nest building has historically been assumed to be largely genetically predetermined and inflexible. However, we believe that the ability to learn about which materials work best and refine building techniques would be so advantageous for improving the nest structure and therefore reproductive success, that learning and memory are probably more important to this process than has previously been considered. We are currently investigating the role of learning and memory in material choice and nest construction behaviour in both Weaverbirds and Zebra Finches.The nest below was constructed by and adult male Southern Masked weaverbird in Botswana.
That birds’ build camouflaged nests is well known, but whether this results from birds paying attention to the characteristics of their nest site and trying to find building material to match or simply from birds building with locally available materials that just happen to be camouflaged, had never been tested.
We wallpapered male zebra finches’ cages in one of five different colours and them gave them two colours of building material, one that matched the wall paper and one that did not. Most of the birds predominantly chose the colour of building material that matched the wallpaper indicating that birds pay attention to the colour of their nest sites and actively chose building material to match. This means that some of the variation we see within species in the wild in what materials they choose to build with may be due to individuals actively selecting locally camouflaged materials rather than just building a ‘standard’ nest and ‘hoping’ that it will be hard for predators to spot.
Read the full story published in AUK: http://research-repository.st-andrews.ac.uk/bitstream/10023/5517/3/Bailey_auk_14_77_1.pdf
Birds’ decisions about what nest-materials to use to build with have typically been considered to be genetically determined. We believed learning may also be important in nest material selection as birds are known to use learning to improve the quality of their decision in many other contexts.
We gave zebra finches lengths of either a stiffer or more flexible sort of white cotton string to build with. After they had some experience of building with their allocated string type, we then gave them a choice of both sorts of string to build with. We observed that those zebra finches that had previous building experience of the more flexible sort of string avoided it and opted to build with the stiffer string, whereas those birds that had only experienced the stiffer string were less choosy. We also noticed that birds who built nests out of the stiffer sort of string required fewer pieces of it to construct a typical zebra finch nest than birds that built nests with the more flexible sort of string, indicating that the stiffer sort of string was a more efficient nest building material.
If birds’ nest-material decisions had been entirely based on their genes then their prior building experience should not have affected their decisions. That it did shows that learning about what materials work best is, as we expected, important in their nesting building decisions.
Read the full story in the Proceeding of the Royal Society- B: http://rspb.royalsocietypublishing.org/content/281/1784/20133225.full
To implicate regions of the brain in nest construction behaviours, Zach Hall looked for correlations between levels of neuronal activity in different brain regions and the performance of nest building behaviours in male and female zebra finches. He measured regional neuronal activity by quantifying the number of cells expressing FOS, a protein expressed in neurons following periods of high activation (see diagram below).