Biology session

The extension of the cities thrives all around the world. As a result of this, natural habitats are changing continuously thus animals must adapt to these changes.

The populations of the great tit (Parus major) living in the urban sites have a lower breeding success compared to those living in the forest sites and it is not compensated by their nesting success. However, previous studies support the idea that they have a higher density exceeding that of the forest populations. One possible reason for the contradiction is that great tits who live in the cities have better chance for survival than those who live in the forests.

In our research we tested two forest (Szentgál, Vilma-puszta) and two urban populations (Veszprém, Balatonfüred). We collected re-capture and re-sighting data from 626 birds in the breeding season during five years and analysed them with Cormack-Jolly-Seber models. We tested the effects of the area, sex and the year for the annual survival and recapture probability.

The recapture probability was constant, but the survival was dependent on the nesting area and the year. The avarage annual survival probability of the great tits was 0.454 according to the best model. The effect of urbanization was not consistent because we found the highest survivals in Veszprém, one of our city areas. In Balatonfüred we had the lowest survivals, while in the case of our two forest areas we always received a value that was somewhere between the values of the two city sites. We found considerable difference between the years. In 2015 we found much lower survival probabilities in all the areas compared to the rest of the periods. The effect of sex on the survival was only detectable when we analysed the areas separately. In Veszprém and Szentgál, one city and one forest habitats, models estimated that the females had a higher survival probability while in Balatonfüred and Vilma-puszta we estimated higher survivals for the males. This result suggests the idea that in the case of great tits the effect of sex on the survival can be changed by the environment. Based on our experiments, it is not the urbanization of the habitat that has an impact on the annual survival as we found remarkable differences between distinct cities. Further investigation should be carried out to detect the role of various environmental parameters.