Ornithol Sci 13: 83 – 90 (2014) ORIGINAL ARTICLE Testing the effect of migratory restlessness on the occurrence of vagrant continental passerines in Japan Yusuke UMEGAKI# Faculty of Human Life and Environment, Nara Women’s University, Kita-Uoya-Nishimachi, Nara City 630–8506 Japan ORNITHOLOGICAL Abstract Many vagrant passerines from the Western Palearctic have been docu- mented in Japan. In the present study, I tested the following two hypotheses: (1) SCIENCE the vagrancy of continental passerines migrating to Japan is affected by migratory © The Ornithological Society distance and migratory direction, rather than distance from the normal distributional of Japan 2014 range; and (2) the vagrancy of continental passerines migrating to Japan is related to migratory restlessness. Data on vagrants were collected from various sources, and the effects of migratory distance, distance from the normal distributional range, migratory restlessness, migratory direction, and normal distribution size were examined. The results revealed significant positive effects of migratory distance and migratory rest- lessness, with these effects being significant even when the effects of other variables were controlled. The normal distribution size had a marginally significant positive effect, but none of the remaining variables predicted the occurrence of vagrants. The vicinity of the normal distributional range of continental passerines was not a predic- tor of vagrancy. These findings indicate that the endogenous migratory program of individuals is responsible for the occurrence of vagrants in Japan, and that sufficiently restless birds may reach the Far East. Key words Japan, Migratory restlessness, Passerine, Reverse orientation, Vagrancy Some Siberian passerine species have been (Prunellinae), and shrikes (Laniidae) (Thorup 2004). recorded in Europe on a relatively regular basis Although many vagrants from the opposite end of and, in some cases, in large numbers. For example, the continent are known to occur in northwest and Pallas’s Leaf Warbler Phylloscopus proregulus and central Europe, data are lacking on the occurrence the Yellow-browed Warbler Phylloscopus inornatus of vagrants in Asia. Nevertheless, a similar situation breed in eastern Siberia (thousands of kilometers occurs in East Asia. Some birds from the Western from Europe) and winter in Southeast Asia; how- Palearctic are documented fairly regularly in Japan. ever, both species are regularly recorded in north- According to the latest checklist of Japanese birds west Europe. In some autumns, more than 300 of the (Ornithological Society of Japan 2012), the number former and 1,000 individuals of the latter species, of Western Palearctic passerine species recorded in may be documented in the United Kingdom alone Japan is high. Even birds with a normal distributional (Fraser & Rogers 2006). Some Asian passerines are range thousands of kilometers west of Japan, e.g., also recorded relatively regularly in northwest and the Wood Warbler Phylloscopus sibilatrix and the central Europe, particularly in autumn (Pfeifer et Meadow Pipit Anthus pratensis, have been recorded al. 2007). These birds mainly include leaf warblers more than 10 times. Other species, such as the Mistle (Phylloscopus), thrushes (Zoothera and Turdus), Thrush Turdus viscivorus, Whinchat Saxicola rubetra, pipits (Anthus), and buntings (Emberiza) (Pfeifer and European Pied Flycatcher Ficedula hypoleuca, et al. 2007), in addition to warblers (Sylviini), fly- have also been recorded more than once. Although catchers (Muscicapini), chats (Saxicolini), accentors some view these vagrants as mere curiosities, only to meet their fate in an unknown place, others claim (Received 18 November 2013, Accepted 12 August 2014) that these records call for scientific evaluation. Veit # Corresponding author, E-mail: [email protected] (2000) and Pfeifer et al. (2007) suggest that scien- 83 Y. UMEGAKI tific evaluation of the causes and consequences of individual causes long distance vagrancy, which con- vagrancy among birds may aid the elucidation of trasts with the weather hypothesis in which vagrancy avian population dynamics. In this regard, the occa- is attributed to external factors such as wind. sional occurrence of the Cattle Egret Bubulcus ibis Support of the reverse orientation hypothesis in South America (Maddock & Geering 1994) and by many studies has led to the assumption that an the House Finch Carpodacus mexicanus in eastern erroneous endogenous migratory program is partly North America (Veit & Lewis 1996; Veit 2000) pre- responsible for vagrancy in some individuals. Pfeifer ceded these species colonizing these areas. Studying et al. (2007) showed that migratory restlessness, not the occurrence of vagrants may thus provide insights distance from the normal breeding grounds, predicts into on-going distributional changes of certain spe- the occurrence of vagrants in Europe, with the authors cies. In addition, studying vagrancy may enhance suggesting that a combination of the migratory pro- our understanding of the migratory system of birds gram and associated restlessness are important fac- (Rabøl 1969; Thorup 2004). tors that determine the occurrence of certain vagrant Several hypotheses have been proposed to explain species. This finding supports the fact that, in central the occurrence of vagrants in extralimital areas. For or northwest Europe, the incidence of vagrants from instance, the weather hypothesis assumes that certain Siberia is higher than that from the Mediterranean weather conditions, such as anticyclones, transport (Thorup 2004). Thorup (2004) has also shown that vagrants to distant locations (Baker & Catley 1987). the occurrence of vagrants in Europe is influenced In Japan, prevailing westerly winds are generally by migratory direction. Birds that migrate eastward in believed to bring Western Palearctic birds. However, autumn from their breeding grounds, mostly in eastern birds are known to select favorable wind conditions Europe, are more likely to occur in northwest Europe. to save energy during migration (Liechti 2006). Fur- Therefore, it may be assumed that, in autumn, an error thermore, it has been reported that vagrant passerines in the migratory program drives individuals of certain from Siberia occur in Europe, even in years with- species on the great circle route. In addition, only birds out strong easterly airstreams (Gilroy & Lees 2003; that are sufficiently restless will reach Europe, because Pfeifer et al. 2007). In Japan, some vagrants from the short-distance migrants will stop at some point along Western Palearctic occur almost every autumn and the erroneous route before reaching Europe. even in years when westerly winds are not strong. On the basis of these assumptions, the continental Even though weather invariably plays a role in deter- vagrants recorded in Japan may be birds that are suffi- mining the abundance of vagrants (Moss 1995; Gilroy ciently restless such that they reach the Far East. This & Lees 2003), wind drift alone does not offer a sat- is because short-distance migrants will stop at some isfactory explanation for the occurrence of vagrants. point along their erroneous migratory route before Alternatively, the misorientation of migratory reaching Japan. Furthermore, continental birds that birds may account for vagrancy. One of the most reach Japan will have a vagrancy shadow (a reverse well-known examples of misorientation is the projection of species’ regular migratory trajectories; reverse orientation hypothesis, in which the autum- Cottridge & Vinicombe 1996) that includes Japan. nal occurrence of vagrants is explained by reversed Thus, it may be possible to predict vagrancy by using long-distance migration from the normally expected existing knowledge about migratory directions. This direction (Rabøl 1969). It is believed that some birds study aimed to test the following hypotheses: (1) the follow the great circle route (Alerstam & Pettersson autumnal vagrancy of continental passerines migrat- 1991; Thorup 1998), which would lead East Asian ing to Japan is predicted by migratory distance and species to central or northwest Europe. The reverse migratory direction, but not by distance from the orientation hypothesis appears to fit well with the normal distributional range; and (2) the autumnal vagrancy patterns of some species recorded in north- vagrancy of continental passerines migrating to Japan west Europe (Rabøl 1969; Thorup 1998, 2004; Pfeifer is related to migratory restlessness. et al. 2007). Despite some skepticism (e.g., Gilroy & Lees 2003), reverse orientation has been supported MATERIALS AND METHODS by various studies (Sandberg 1994; Thorup 1998; 2004; Pfeifer et al. 2007; Thorup et al. 2012). The 1) Definition of continental vagrants reverse orientation theory is based on the concept that On the basis of the studies by Thorup (2004) and an error in the endogenous migratory program of an Pfeifer et al. (2007), I included all Eurasian spe- 84 Vagrant continental passerines in Japan cies belonging to four passerine genera: Lanius, 2) Records of vagrants Phylloscopus, Turdus, and Anthus. The four genera Databases containing records of the selected were selected because (1) each genus consists of vagrant species in Japan are not available. There- balanced numbers of common, regular, vagrant, and fore, I collected all available records to generate a unrecorded species from Japan, and (2) these gen- database. Data were extracted from various sources, era have also