Food hoarders and non-hoarders in Paridae - a cognition perspective.

Parids are well-known birds both in Europe and North America. Despite being arboreal foragers of similar size, there is a striking dichotomy in the wintering strategies in the family. Most species are food hoarding specialists that store large amounts of winter food in autumn. A small stable group will then defend a large winter territory in which they store food. From a cognition perspective these species are spatial memory specialists with the volume of the hippocampus, a brain structure that is important for spatial memorization, correlating to the degree of specialisation for food hoarding. The wintering strategy in non-hoarding parids, the Eurasian great and blue tits, and species that are closely related to these, is very different. They are generalist foragers that have adapted especially well to anthropogenic habitats such as gardens and city parks. The great tit stands out as being especially innovative and good at observational learning, deserving its reputation as being "smartest among tits". As the great and blue tits do not occur in North America it is possible that some chickadee populations have adapted to anthropogenic habitats as opposed to their Eurasian close relatives. The black-capped chickadee, for example, has been observed mastering foraging techniques that only the great tit does in Europe. In conclusion, there is a trade-off between two cognitive specialisations in the family with hoarding parids being spatial memory specialists and non-hoarding innovative problem solvers. The starkness of this dichotomy probably depends on that the selection for optimal foraging in winter is especially strong in small birds.