Stopover Strategies of Eurasian Blackcaps (Sylvia Atricapilla) During the Post-Fledging Period in Western Hungary

Ornis Fennica 94: 180193. 2017 Stopover strategies of Eurasian Blackcaps (Sylvia atricapilla) during the post-fledging period in western Hungary József Gyurácz*, Péter Bánhidi, József Góczán, Péter Illés, Sándor Kalmár, Zoltán Lukács, Csaba Németh, Péter Molnár & László Varga J. Gyurácz, Z. Lukács, P. Molnár, Eötvös Lorand University, Savaria Campus, Depart- ment of Biology, Szombathely, Károlyi Gáspár tér 4. H-9700, Hungary. *Corresponding authors e-mail: [email protected] P. Bánhidi, J. Góczán, P. Illés, S. Kalmár, Cs. Németh, L. Varga, Local Groupof BirdLife Hungary, Szombathely, Károlyi Gáspár tér 4. H-9700, Hungary Received 11 January 2017, accepted 30 September 2017 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. This might be particularly important in populations that are increasing, which is the case for the Blackcap. Our data support the idea that most Blackcaps were using the study site at Tömörd as a stopover area, but only a small number of them were using it as a site specifi- cally to fatten up. 1. Introduction research should focus on stopover strategies of birds, and ringers should undertake more recaptur- Migration of birds is divided into two main peri- ing and reweighing of birds during their stopovers ods; non-stop flight during which their energy re- (Bairlein 2003a). There is a need to collect more serves are depleted, and stopovers during which data on the relationship between fuel-deposition they need to rest and refuel their fat stores (Newton rate and departure fuel load in retrapped birds dur- 2011). Migratory birds spend about 90% of their ing migration, because migrant passerines need to whole migration time at stopovers and substantial accumulate sufficient fuel before undertaking en- mortality occurs during these periods (Heden- ergetically demanding migrations. Successful mi- ström & Alerstam 1997). Therefore, much more gration depends on time, energy or riskof preda - Gyurácz et al.: Stopover strategies of Eurasian Blackcaps in western Hungary 181 tion minimizing strategies (Alerstam & Lindström portion of Blackcaps, both during dispersal and in 1990, Chernetsov 2012). the migration periods, pass through the Carpathian At stopover sites, birds must find adequate Basin. The timing of their autumn migration food supplies that can be utilized for net energy shifted about two weeks later during the last 25 gain, therefore analysis of stopover has great im- years in Hungary (Kovács et al. 2010). The Hun- portance for understanding the behavior of mi- garian populations are migratory and the wintering grant species (Biebach et al. 1986, Ellegren & areas are in the eastern and central Mediterranean Fransson 1992, Bairlein 2003b). Survival of mi- territories (Csörgõ & Gyurácz 2009). grants may be affected by morphological and The trans-Saharan migrants exhibit four types physiological quality, sex, age, social status or ex- of fattening patterns during autumn migration perience (Moore et al. 2003). There are frequent (Schaub & Jenni 2000): 1) accumulate large fat relationships between migration and social domi- stores and fly non-stop from the northern edge of nance among passerines, raptors and seabirds the Sahara to sub-Saharan Africa (time minimi- (Catry et al. 2004, Newton 2011). According to zation model), 2) accumulate more fuel at each some studies, males often fatten more rapidly and stopover site and fly from one site to the next, 3) stop over for a shorter time than subordinate fe- migrate in short stages with accumulation of suffi- males on stopover sites, which is due to the greater cient fat to fly to the next stopover site, 4) similar inedominance of males (Morris et al. 1994, Otahal strategy as the third, but these birds stopover at 1995). desert oases or catch migrant insects (2, 3 and 4 are However, sex differences have not been ob- energy and predation minimization models). Male served in all passerines and at all stopover sites Blackcaps follow a time-minimization strategy, (Maitav & Izhaki 1994). Food availability deter- while females place more importance on energy- mines how fast and to what extent refueling takes maximization during spring migration (Yosef & place (Ellegren 1991, Fransson 1998, Dänhardt & Wineman 2010). Lindström 2001): when food is abundant, the ef- However, the positive relationship between fect of social status or scramble competition could departure body mass and mass deposition rate sug- be negligible (Moore & Yong 1991). Also, within gests a time-minimizing stopover strategy during a species, stopover duration can vary with year, autumn (Arizaga et al. 2008). In this study, over 18 site and fuel load (Biebach et al. 1986, Moore & years of recapture data were analyzed to improve Kerlinger 1987, Kuenzi et al. 1991, Gannes 2002). knowledge on stopover duration, body mass and The analysis of fat deposition at stopover sites may fat store changes. Considering types of migration explain how a species balances costs and benefits, strategy and earlier European studies, we suggest and can clearly reveal the species migration strat- the time-minimization model for the autumn mi- egy (Yosef & Wineman 2010). gration of the Blackcap sex classes during post- The Eurasian Blackcap (Sylvia atricapilla)isa fledging period in western Hungary. common passerine in Europe (Cramp 1992) and ringed in large numbers at European ringing sites We asked the following questions: (Berthold & Solenen 1997). Studies of its stopover ecology at some ringing sites in central Africa (1) What proportion of birds is retrapped in the (Hjort et al. 1996), the Middle East (Maitav & study area? Izhaki 1994, Izhaki & Maitav 1998, Gannes 2002, (2) What is the average stopover length of retraps? Erciyas et al. 2010, Yosef & Wineman 2010) and (3) Does the average stopover length differ be- Europe (Lövei et al. 1985, Turrian & Jenni 1991, tween sex classes? Ellegren & Fransson 1992, Grandío 1997, Arizaga (4) Do the amounts and rate of body mass gain and et al. 2008) have already been reported. Studies fat deposition differ between males and fe- are particularly scarce in Central Europe, although males? the region has a high interest for stopovering (5) What factors determine the length of stopover Blackcaps. Recaptured birds originally ringed in period and rate of body mass gain and fat depo- Scandinavia and Poland show that a certain pro- sition? 182 ORNIS FENNICA Vol. 94, 2017 2. Materials and methods the nearest 0.1 g using a digital balance. The fat re- serves (fat score) were estimated visually accord- 2.1. Study site ing to the SE European Bird Migration Network protocol (Busse & Meissner 2015) ranging from The study was carried out at the Tömörd Bird 0 (no fat) to 8 (bulging fat).As adult Blackcaps Ringing Station in western Hungary (47°21N were captured in small numbers, we pooled the 16°40E), located 15 kilometers from Szomba- data of age groups for both sexes. The condition thely. There are four natural habitat types around index (CI) was calculated according to Swanson the station of Tömörd. Bushes: bushes and herbs et al. (1999): are made up of compact, dense vegetation, which is dissected by small grass patches. Its characteris- CI = body mass/wing-length tic plant is the blackthorn (Prunus spinosa L.).Fo- rest: broadleaf trees and bushes show compact, To avoid the effect of body mass changes in the dense edge vegetation, forming an ecotone com- diel cycles (Winker et al. 1992), only data from munity with turkey oak (Quercus cerris L.) as the birds captured during the morning period were characteristic plant. There are plenty of crops and used. The individual capture dates were not stan- normal forestry management in the forest. Grass- dardized to the mean arrival date for the given year land with scrubs: this habitat type represents a (Yosef & Wineman 2010). transition between the wet habitats of the swamp In order to enable comparisons with other stud- and the steppe communities that used to cover the ies, minimum stopover length was defined as the croplands around the marsh. There are a few period from the date of first capture to the date of bushes in the grassland with two small patches of last recapture (Ellegren 1991). It should be noted dwarf elder (Sambucus ebulus L.). The grassland that this is often less than the stopover duration as is not managed. Marsh: a small (6 ha), permanent, assessed by Cormack-Jolly-Seber models (Kaiser and isolated wetland. The characteristic plant is 1999, Schaub et al. 2001). The body mass at the reedmace (Typha latifolia L.) in the marsh. first (arrival body mass, ABM) and last capture event (departure body mass, DBM) were available for each recaptured bird. Difference between 2.2. Data collection and analysis DBM and ABM was used to assess the mass deposition rate (MDR). The departure fuel load was The birds were captured-recaptured and ringed calculated as the percentage over lean body mass, from 1998 to 2015 (Appendix 1). Bird ringing LBM, i.e., mean body mass of individuals with tookplace during the post-fledging period (dis - zero fat score (Arizaga et al.

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