We ran across the news report for an interesting study of bird nest building, which illustrates the common misconception that an instinct requires a rigid pattern of behavior.
The title is "New study says birds learn how to build nests."
I am certainly prepared to believe that a bird can improve its nest building with practice. In fact I would expect that to happen. How could it not?
The problem is that the researcher's evidence for this conclusion seems to be merely that individual birds built nests that varied over time. It is not that these successive nests got better over time, just that they varied, or so it seems from the news account.
One of the researchers -- Dr Patrick Walsh of Edinburgh University -- is quoted as saying "If birds built their nests according to a genetic template, you would expect all birds to build their nests the same way each time. However, this was not the case."
Dr. Walsh is simply mistaken about the supposed lack of flexibility in genetic templates. Instinct is expertise applied to a given situation. As the situation varies, so may the outcome.
For example, I have a bird's nest made completely of horse hair. I have another made from unwinding the filaments that coat Christmas bulbs, a very colorful example of the use of materials. I am sure there are no birds that depend on either of these materials. They merely used what was readily available.
I have also seen beaver dams made from very different materials. In one case our beavers built many dams using the materials from a grove of mature aspen trees, which they first felled. This dam included quite a few branches up to three inches in diameter. In the same area another set of dams, possibly built by the same pair of beavers, consisted entirely of saplings, as there were no mature poplar trees in the area. These constructions were very different, because the situations were different.
The point is that these instinctive activities allow for a great deal of local reasoning. That a bird, or a beaver, should build the same thing, the same way, every time is an incorrect view of how instincts work. An instinct is a body of expertise, not a specific set of behaviors. It is how to do something, not what to do in every different situation.