A general warming of climate in the future may profoundly affect wildlife populations in terms of numbers, distribution and characteristics of the individuals, therefore leading to new challenges in terms of management and conservation. The effects of global warming can already be detected through the analysis of long-term databases, but insights into these processes can also be acquired by studying changes in wildlife populations during periods with clear trends in climatic changes. We analysed ringing data from more than 38,000 teal Anas crecca caught at the Station Biologique de la Tour du Valat in the Camargue, Southern France, between September 1954 and April 1971. Temperature in the Camargue clearly decreased over the ringing period. There was no correlation between average annual body mass and temperature in any age or sex class, nor a significant effect of temperature on the age ratio of the population. In adults, there were more males when average daily maximum winter temperature increased, while the opposite trend was found for juveniles. The clearest pattern we observed was a positive relationship between temperature and wing length of the individuals: in all sex and age classes, birds tended to get smaller as temperature decreased. It is unlikely that this pattern was related to harsh climate affecting teal feather growth. Rather, we hypothesise that climate affected the distribution of the individuals in Europe: as temperature got colder, small birds found it still more difficult to remain in northern areas and increasingly used the Camargue as a refuge. Reversing the observed pattern suggests that a global warming of climate in the future may have profound consequences for the distribution of wintering teal in Europe, as more and more birds will become able to remain in northern areas closer to their breeding grounds.