Biology session

In recent decades, the pattern of migration of several passerine bird species has been changed. These changes are also detectable at long distance migrant species having less plastic behaviour, and being under strong genetic control. In our study we’ve used the long term ringing datasets of the Ócsa Bird Ringing Society to compare the migration phenology of two closely related long distance migrant flycatcher species, the pied flycatcher (Ficedula hypoleuca) and the spotted flycatcher (Muscicapa striata). In the recent decades these species had strong population decline. It’s reasonable to study the changes in the migrating and wintering conditions, since the reason of the declanation is presumably in these circumstances. The birds are caught with mist nets under standard conditions. We treated the age groups at both species and at the pied flycatcher, because it’s possible to determine based on plumage, the sexes separately during the analysis. We’ve used quantile regression to study the changes in timing of migration and the relationship between timing and the biometrics of the birds, and linear regression to analyse the changes in the biometrics. We compared wing length of bird’s caught in spring and in autumn with Welch-test. The relationship between the median of spring and autumn arrival times and mean monthly minimum and maximum temperatures and mean monthly precipitation calculated for the study period has been studied.

In our results the timing of spring migration has been shifted earlier and the timing of autumn migration later in both species. The probable reason of these phenomenon are the shift in the spring and autumn weather conditions and the vegetation period affecting the spring gradation of the food taxas. The relationship between the timing and wing length is different at the two species. In case of pied flycatcher the longer winged individuals arrive earlier in spring and the shorter winged ones in autumn, in case of spotted flycatcher longer winged individuals arrive earlier in both periods. In both species the lighter on average individuals arrive earlier to the study area. Probably the migrating populations are different in spring and autumn meaning - in accordance with western European studies - that pied flycatcher is a loop migrant using different routes in the two periods. In case of spottted flycatcher we can hardly draw conclusions. It’s possible, that the difference between the timing of sexes or the leap-frog migration strategy makes this pattern. The cause of the increase in average wing length could be the raised ratio of trans-migrant individuals originated from northern populations. We couldn't find significant relationship between local weather variables and migration timing. An explanation is that local meteorogical variables are possibly not adequate indicators of the effects of climate change on bird migration.