A Southern Masked Weaverbird nest building in Botswana
Building on Experience
There are thousands of species of birds, most of which build nests. Some nests, like those of swallows, are made through spitting out mud and binding it together. Other birds like hummingbirds use spider webs to hold their nests together. My personal favourite is the tailorbird, which actually sews both edges of a large leaf together using silk to make its nest.
But how do birds know how to build nests? In humans, building a house or even making a bed is something that we learn to do through practice. We might copy our parents doing it, or learn from watching others over time. We also often have an image in mind of what we are trying to achieve, so that we don’t just start building mindlessly and end up with an igloo instead of castle. Whether birds do anything at all similar to us is something we know very little about.
In weaverbirds, the magnificent birds pictured here, the male builds a nest and then uses it to attract a female. The male rips off a long, fresh strip of grass, and knots it to a branch. He then adds more grass strips, weaving them together using stitches also used by humans. Weaving is a complicated business, involving his beak and both feet. As he weaves the female inspects his work, if his nest impresses her then she will mate with him. As soon as a male secures one female, he will start building again to try and obtain another one.
A male Zebra Finch -an important part of building a nest is choosing the right materials.
Not all nests are as striking as those of weaverbirds. Zebra finches build nests that at first glance appear less impressive, yet even when building these humble abodes it helps to learn a trick or two. An important part of building a nest is choosing the right materials. Like the weaverbirds, it is zebra finch males that choose the nest materials, although in this case the female will also get involved in the actual building of the nest. Zebra finch males have particular preferences for what colour of nest material they choose to build their nest from. However, they learn through experience which materials work better for a nest and can change their preferences accordingly.
For example, if a male initially did not choose a colour (say, green) to build with, but was then given only this colour to build a nest out of, and it then resulted in successful breeding, he chose this colour in the future. On the other hand, if he built a nest out of this colour and then his eggs were removed before the chicks hatched, he did not change his behaviour and choose this colour in the future.
This finding that zebra finches learn about the nest material they choose to build with is but one piece to the puzzle. However, it does show that birds can be flexible in their nest building behaviour. Future experiments will reveal even more about how birds know how to build nests.