Do experiments with captive non-domesticated animals make sense without population field studies? A case study with blue tits' breeding time

A complete understanding of the spatio-temporal variation in phenotypic tra its in natural populations requires a combination of long-term field studie s with experiments using captive animals. Field studies allow the formulati on of realistic hypotheses, but have the disadvantage that they do not allo w the complete control of many potential confounding variables. Studies wit h captive animals allow tests of hypotheses that cannot be examined in the field, but have the disadvantage that artificial environments may provoke a bnormal behaviour. Long-term studies that follow simultaneously captive and wild bird populations are rare. In a study lasting several years, we show here the unexpected patterns that two populations with a similar breeding t ime in the wild have non-overlapping breeding times in outdoor aviaries, an d that two wild populations separated by a short geographical distance show differences in the expression of natural behaviour in captivity. The exper imental design used is exceptional in the sense that the captive population s were held at similar latitudes and altitudes as the wild populations. Our case study shows that studies with captive animals can lead to wrong concl usions if they are carried out without population field studies, and withou t knowledge of the natural habits and habitats of the species involved. To examine the reliability of experiments with captive animals, comparisons wi th findings from population field studies are essential.