The UK has a longstanding milk distribution system in which milkmen in small trucks bring the milk in bottles to the door of each country house. At the beginning of this century, these milk bottles had no top. Birds had easy access to the cream which settled in the top of the bottle. Two different species of British garden birds, the titmice and the red robins, learned to siphon up cream from the bottles and tap this new, rich food source.
This innovation, in itself, was already quite an achievement. But it also had revolutionary effect. The cream was much richer than the usual food sources of these birds, and the two species underwent some adaptation of their digestive systems to cope with the unusual nutrients. The internal adaptation almost certainly took place through Darwinian selection.
Then, between the two world wars, the UK dairy distributors closed access to the food source by placing aluminium seals on the bottle.
By the early 1950s, the entire titmouse population of the UK – about a million birds – had learned how to pierce the aluminium seals. Regaining access to this rich food source provided an important victory for the titmouse family as a whole; it gave them an advantage in the battle for survival. Conversely, the red robins, as a family, never regained access to the cream. Occasionally, an individual robin learned how to pierce the seals of the milk bottles, but the knowledge never passes to the rest of the species.
In short, the titmice went through an extraordinarily successful institutional learning process. The red robins failed, even though individual robins had been as innovative as individual titmice.Moreover, the difference could not be attributed to their ability to communicate. As song birds, both the titmice and the red robins has the same wide range of means of communication: colour, behaviour, movements, and song. The explanation, said Wilson, could be found in the social propagation process: the way titmice spread their skill from one individual to members of the species as a whole.
In spring, the titmice live in couples until they have reared their young. By early summer, when the young titmice are flying and feeding on their own, we see the birds moving from garden to garden in flocks of eight to ten individuals. These flocks seem to remain intact, moving together around the countryside, and the period of mobility lasts for two or three months.
Red robins, by contrast, are territorial birds. A male robin will not allow another male to enter its territory. When threatened, the robin sends a warning, as if to say, “keep the hell of here”. In general, red robins tend to communicated with each other in an antagonistic manner, with fixed boundaries that they do not cross.
Birds that flock seem to learn faster. They increase their chances to survive and evolve more quickly.