Reproductive differences between urban and forest populations of great tits

Prof. András Liker

MTA-PE Evolutionary Ecology Research Group, University of Pannonia, Veszprém, Hungary

Date: Wednesday, 09.01.2019, 13:00, Cent Lecture Theatre 0142                                         How to get there: Lecture theatre 0142 is c. ~15 meters to the right after entering CeNT

Abstract. Urban birds often have lower reproductive success but higher densities than their conspecifics living in natural habitats, and it is still unclear what processes explain this paradoxical pattern. In a study started in 2012, we found that great tits breeding in two urban populations produce consistently fewer nestlings than birds in two nearby forest populations. This difference is likely explained by lower abundance/quality of nestling food in cities than in forests, because in cities (1) caterpillar biomass on trees is 8-20 times lower, (2) caterpillars constitutes a smaller part of nestling diet, and (3) although food volume per nestling shows no habitat difference, nestlings size and mass is lower. Furthermore, a food supplementation experiment showed that supplemented urban nestlings can achieve size and survival rate similar to control forest nestlings, whereas extra food has no effects on forest nestlings. The analyses of the frequencies of second broods suggest no habitat difference in the annual number of broods produced by individual females, and we also did not find consistent differences in the survival rate of breeding adult birds between cities and forest populations. Thus, the persistence and high densities of urban great tit populations can be related to higher survival rates of younger age classes (e.g. fledglings or first winter birds) and/or to immigration from surrounding natural habitats.

Photo credit: Bálint Preiszner