The fieldwork, i.e. catching and ringing birds using mist-nets, was conducted at Tömörd Bird Ringing Station in western Hungary during the post-breeding migration seasons in 1998-2016. Altogether, 106,480 individuals of 133 species were ringed at the station. The aim of this paper was to publish basic information on passerine migration at this site. Migration phenology was described through annual and daily capture frequencies. Furthermore, we provide the median date of the passage, the date of the earliest or latest capture, the peak migration season within the study period, and the countries where the birds monitored at the site were ringed or recovered abroad. To compare the catching dynamics for the fifty species with total captures greater than 200, a reference period was defined: from 5 Aug. to 5 Nov. 2001-2016. Some non-passerines that are more easily caught with mist-nets or that are caught occasionally were listed as well. The two superdominant species, the European Robin and the Eurasian Blackcap, with 14,377 and 13,926 total captures, made up 27% of all ringed individuals. Among the fifty species analysed, there were ten species with a decreasing trend, five species with an increasing trend and thirty-five species with a stable (or uncertain) trend in their numbers from 2001 to 2016. The temporal pattern of migration of long-distance migrants was different from that of the medium- and short-distance migratory species.

Changes in biometric characteristics of a migrating bird population at a given capture site could reflect that the migration strategies of the species may be changing. A robust data set (15,520 records) was used to analyse the changes in biometric characteristics of the Eurasian Blackcap Sylvia atricapilla in western Hungary between August and October during the study period (2001–2019). All age and sex classes displayed similar phenology of monthly captures and biometric change: the average wing length, fat score and body mass increased in the migrating population from August to October. This could be explained by changes in the morphometric distribution of different migrating populations, in later months more birds might arrive from a larger distance, primarily from the Baltic regions and the Czech Republic. The biometrics of juvenile birds captured in August did not change significantly from 2001 to 2019, while the wing lengths decreased and fat scores increased significantly between 2001 and 2019 in September and October in both sex classes. This could be explained by a change in the migration distance or different morphology of individuals from the north which stopped over at the study area. Due to the global warming and habitat changes in the last decade, the shorter migration route and favourable conditions at overwintering areas north of the Sahara or around the Mediterranean could favour Blackcaps which migrate a shorter distance.

Estimating fuel load and potential flight ranges of migrant passerines are basic issues in understanding bird migration strategies. Thirteen sub-Saharan and three pre-Saharan migrant passerine species were analysed in this study. The birds were captured at the Tömörd Bird Ringing Station in the western part of the Carpathian Basin. A general linear model with body mass as the dependent variable and fat score, muscle score and wing length as independent variables were used to estimate lean body mass (body mass without fuel deposits) and fuel load. In ten of the species studied, models considering interactions between factors fit the data better than the main-effect models. Body mass was positively correlated with the fat score in all species, with muscle score in ten species and wing length in 14 species. During autumn, fuel load tended to be larger in the sub-Saharan migrants, especially in four species which pass over the Mediterranean Sea, Common Nightingale (Luscinia megarhynchos), Icterine Warbler (Hippolais icterina), Garden Warbler (Sylvia borin) and Barred Warbler (Curruca nisoria). Nine sub-Saharan migrants, Marsh Warbler (Acrocephalus palustris), Sedge Warbler (A. schoenobaenus), Eurasian Reed Warbler (A. scirpaceus), European Pied Flycatcher (Ficedula hypoleuca), Spotted Flycatcher (Muscicapa striata), Wood Warbler (Phylloscopus sibilatrix), Willow Warbler (Ph. trochilus), Common Whitethroat (C. communis) and Lesser Whitethroat (C. curruca) had estimated flight ranges similar (<1300 km) to two pre-Saharans, European Robin (Erithacus rubecula) and Eurasian Blackap (S. atricapilla). The three short-distance migrants, including the Common Chiffchaff (Ph. collybita) with the shortest distance, had sufficient fuel load to reach their southern European wintering sites without needing to refuel at stopover sites.

Stopover strategies of the Eurasian Blackcap (Sylvia atricapilla) during the post-fledging period were studied at Tömörd, western Hungary, between 1998 and 2015. Capture data of juveniles and adults were pooled for both sexes, and recapture rate, stopover length and fat deposition patterns were analyzed. During stopover, males and females did not differ significantly in stopover length, total change in body mass, proportion or rate of body mass change, or change in fat score. Among all recaptures, an overall significant positive correlation was recognized between mass deposition rate (g/day) and departure body mass. According to our results, both males and females use a time-minimization migration strategy in autumn. The benefit of this strategy might be that it favors early arrival in the overwintering areas, before competitors. The individuals arriving earlier at wintering sites might obtain higher-quality territories and achieve higher winter survival.

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Sciendo provides publishing services and solutions to academic and professional organizations and individual authors. We publish journals, books, conference proceedings and a variety of other publications.