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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Changes in the circannual rhythm of selected migratory bird species in and around Hamburg since the 1960s. (2023)
Auteurs :	Ronald Mulsow, Auteur ; Luisa Wieczorek, Auteur
Type de document :	Article
Dans :	Vogelwarte (61(1) 2023)
Résumé :	After numerous publications about changes of the first arrival of migratory bird species, we tried to clarify which changes within the circannual cycle are happening in the study area. For this purpose, we used all available bird records from Hamburg and the surrounding area. We evaluated data of 14 passerine and eleven non-passerine species from the period 1960 to 2021. The data have been collected by the "Arbeitskreis Vogelschutzwarte Hamburg" (Hamburg and surroundings = 2,122 km(2)). Species were selected according to the number of records available for the analysis. Changes in the circannual cycle were evaluated by regression analysis and comparisons between two periods.Results: The date of first arrival shifts forward for 23 out of 24 species. The only species with a delayed arrival is the Garden Warbler. This species, however, has declined strongly, and the delay in arrival time could be an artefact related to the reduced population size. The largest forward shift has been observed for Stock Dove, White Stork, and Eurasian Blackcap. The mean shift for all species was 0.26 days/year, for short-distance migrants (SDM) 18.1 days and for long-distance migrants (LDM) 10.2 days. The difference is statistically significant. As for the comparison between the two periods, the forward shifts for the selected species are more pronounced during the earlier period 1960 to 1990. Comparable data from Berlin show mostly positive correlations. There was a distinct forward shift in the arrival of the 20th record in the year for all species.Territorial behaviour, indicated by the first song or display activity, started earlier for all studied species; the mean period of forward shift amounts to 13.2 days. As expected, the shift was more distinct in SDM. An earlier start of breeding was evident for White Stork and Northern Lapwing. Despite the limited data availability, spring migration showed a general forward shift (median) of 1.7 pentads for all species except Garganey.In contrast to spring migration, the results for autumn migration dates show greater variability. For nine species, there is no change at all, for seven species a forward shift and for seven species a delay. For the Eurasian Reed Warbler, ringing data (number of caught birds) even show a shift in trend: until 2007, there was a trend towards earlier migration, after that year a trend towards later departure. For species that breed only once a year, it might be of benefit to arrive early in the Sahel in order to take advantage of the rainy season, whereas other species may tend to increase the number of offspring by increasing the number of broods.Departure: The mean delay is 18 days for 23 of 24 species, again a longer period for SDM than LDM. Only the European Honey Buzzard shows a forward shift in departure of 2.2 days.Annual recording period: The forward shift of the first observation (12.9 days) and the mean delay of the last observation (18.4 days) result in a prolongation of the period a species is present (and can be recorded) in its breeding area by 31.3 days. The opportunity to realise more broods is used by SDM; in a longer term, this strategy resulted in a population increase. For LDM, besides global warming, habitat changes in the breeding or wintering area probably also affect the decision for earlier or later migration.

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