It is typically assumed that it is a bird’s genes that cause it to choose the materials with which it builds its nest. To test this assumption, Dr Susan Healy and others from the School of Biology investigated whether learning plays a role in these decisions, specifically with regard to whether birds learn the physical properties of the materials they use in nest building.
In their experiments, zebra finches were given lengths of string that were either relatively stiff or relatively flexible. Once the birds had had some experience of building with their allocated string type, the researchers gave them a choice of both types of string. They observed that those zebra finches that had experienced building with the more flexible sort of string preferred to build with the stiffer string, whereas those birds that had experienced only the stiffer string were less choosy. We also saw that the birds that built nests using the stiffer string required many fewer (about 400) pieces to construct a typical zebra finch nest than did the birds that built a nest with the more flexible string (about 700 pieces). This indicates two things: (1) the stiffer string was the more effective nest building material and, (2) the birds readily learned to avoid the poorer 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 important in the decisions made by nest-building birds, much as it is important to people deciding what materials or tools to use for craft or DIY projects. In the wild this ability might allow birds to choose the most suitable material available, allowing them to respond flexibly to the habitat in which they are nesting.
The study, Physical cognition: birds learn the structural efficacy of nest material, is published in the Proceedings of the Royal Society – B.