The tale of the three little tits: Different nest building solutions under the same environmental pressures

Evolutionary selection pressures, and species-specific ecology and behavior, promote a great variability in the size and composition of nests. However, it would be expected that phylogenetically close species, with similar ecological needs, breeding at the same time in the same place, would also build similar nests. In contrast with this, previous studies have found differences in nest mass and composition among closely related sympatric species. These differences have been attributed to small differences in body size (smaller species building larger and/or more insulated nests), or to the different ways in which species perceive the environment (e.g. perceived predation risk). In this study, for the first time, we searched for differences between nest mass, composition, and importance of the different functional parts of the nest between Blue (Cyanistes caeruleus), Great (Parus major) and Coal tits (Periparus ater) breeding under the same conditions. We found that smaller species built larger nests and/or include more thermoregulatory materials, probably having greater insulating capacity, which agrees with previous hypotheses. In particular, Blue Tits made greater use of bark, feathers and vegetable fiber, while Great Tits used wild boar hair in greater proportions. In addition, for the first time, we described in detail the nest composition of Coal Tits, which contained large amounts of fluff compared to the other two species. All these results are in line with previous hypothesis linking nest size and composition to the size of the birds, and the existence of species-specific characteristics in the selection of materials for nest building.