Ornithol Sci 13: 83 – 90 (2014)

ORIGINAL ARTICLE Testing the effect of migratory restlessness on the occurrence of vagrant continental 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 may reach the Far East.

Key words Japan, Migratory restlessness, , 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 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 been considered in previous studies including printed material (e.g., Onishi & Maki 2000; (Thorup 2004; Pfeifer et al. 2007), allowing com- Kawaji et al. 2003; Nihon-san Chorui Kiroku Iinkai parison of the results with preceding studies. The 2005; Onishi & Kuroda 2012; Ornithological Soci- following species belonging to the four genera were ety of Japan 2012) and communications with expert excluded: (1) species with a normal distributional members of the Ornithological Society of Japan and range that includes Japan (common species), e.g., the the Wild Society of Japan (Table 2). I only con- Brown Shrike Lanius cristatus and the Buff-bellied sidered autumn and winter records, i.e., initial sight- Pipit Anthus rubescens; (2) regularly recorded spe- ings reported between August and February. I used cies with a normal distributional range that lies within the sum of all autumn and winter records for each a 1,500-km radius of Japan (uncommon but regular species as an index of the occurrence of each species species), e.g., the Chinese Grey Shrike Lanius sphe- as vagrants. nocercus, Radde’s Warbler Phylloscopus schwarzi, Migratory distance, distance from the normal dis- and the Grey-backed Thrush Turdus hortulorum; (3) tributional range, migratory direction, and population species with autumn/winter records from Japan that size were estimated from data provided by BirdLife are under review by the Ornithological Society of International (2012). When data were not available Japan, i.e., the Song Thrush Turdus philomelos; and in the BirdLife International report (2012), I referred (4) small island breeders, rare local endemics, and to the Xeno-canto Foundation reports (2005–2012) species with a limited or poorly elucidated distri- and relevant monographs (e.g., Alström et al. 2003). butional range, e.g., the Canary Islands Chiffchaff When the maps from these publications depicted dif- Phylloscopus canariensis and the Limestone Leaf ferent ranges, I adopted the smallest range. First, I Warbler Phylloscopus calciatilis. Species previously measured the extent of the breeding and wintering recorded at least once in Japan were considered as ranges in north-south and east-west directions, and continental vagrants. A list of 105 species from the used the point where the two midpoints meet as the four genera was initially generated. From the list, center of the breeding and wintering ranges. The dis- 34 common/regular species were excluded, leaving tance between the center of the breeding and win- 13 autumn/winter vagrants and 58 non-recorded spe- tering ranges was measured to the nearest 500 km cies that were subjected to analysis (Table 1). Spe- (= migratory distance, Fig. 1a). Second, the shortest cies classification was performed according to the distance from the edge of the distributional range to approach by Gill and Donsker (2013). I followed Japan was measured to the nearest 500 km, using BirdLife International (2012) to delineate the distri- Tokyo (Japan) as an arbitrary reference point (= dis- bution of each species. For species without a distribu- tance from the normal distributional range, Fig. 1b). tion map in BirdLife International (2012), I referred Migratory restlessness was estimated by calculating to the monographs of each genus (Baker 1997; the ratio of the migratory distance to the distance Lefranc & Worfolk 1997; Clement 2000; Alström et between the breeding range and Japan (Pfeifer et al. al. 2003). 2007). Third, migratory direction was estimated by drawing a line between the center of the breeding and wintering ranges, and measuring the angle of the line

Table 1. Numbers of common/regular, vagrant, and non-recorded continental passerine species in Japan.

Genus Common/regular species Autumn/winter vagrants Species without records Lanius 6 2 9 Phylloscopus 12 3 32 Turdus 9 5 12 Anthus 7 3 5

85 Y. UMEGAKI - Reference Fig. 1. Migratory distance (a), distance from the normal dis- tributional range to Japan (b), and migratory direction (c) of the Yellow-streaked Warbler Phylloscopus armandii. Original map generated by CraftMAP (http://www.craftmap.box-i.net/).

(Fig. 1c). I used migratory direction as a categorical variable (e.g., SW, SSE). Population size or abun- dance affects vagrancy (Thorup 2004; Newton 2007). Since population size is known to be positively cor- related with distribution size (Gaston 1994), I used normal distribution size (BirdLife International 2012) Onishi & Maki 2000; Ornithological Society of Japan 2012 Ornithological Society of Japan 2012; Shinsuke Takagi personal communication Nihon-san Chorui Kiroku Iinkai 2005; Onishi & Kuroda 2012 Nihon-san Chorui Kiroku Iinkai 2005; Umegaki & Onishi 2012; Onishi Toshikazu personal com - munication Nihon-san Chorui Kiroku Iinkai 2005; Toshikazu Onishi personal communication Iozawa 2000; Hirano 1999–2012 Ornithological Society of Japan 2012; Hirano 1999–2012; Toshikazu Onishi personal communi - Masayuki Senzaki personal communication cation; Kawaji et al., 2003; Toshikazu Onishi personal communication; Shinsuke Takagi personal com munication Kawaji et al., 2003; Shinsuke Takagi personal communication Ornithological Society of Japan 2012 Ornithological Society of Japan 2012; Toshikazu Onishi personal communication Hirano 1999–2012; Toshikazu Onishi personal communication Ornithological Society of Japan 2012 as an index of population size. For species for which the distribution size was not described, I referred to the Xeno-canto Foundation reports (2005–2012) and relevant monographs (e.g., Alström et al. 2003). 11 4 3 77 27 21 2 18 13 17 3 28 1 To test whether species from a certain genus tend to show more frequent vagrancy than those from other genera, the effect of genus was considered as a cat-

Autumn/winter records egorical variable.

3) Analysis Analysis of Covariance (ANCOVA) was conducted to examine the effects of migratory distance, distance from the normal distributional range, migratory rest- lessness, migratory direction, population size, and English name genus on the occurrence of vagrants. Table 3 shows

Red-backed Shrike Isabelline Shrike Warbler Willow Warbler Wood Black-throated Thrush Red-throated Thrush Fieldfare Redwing Mistle Thrush Meadow Pipit Pipit Tree Rosy Pipit the Pearson’s correlation coefficients between the quantitative variables. Because migratory distance and migratory restlessness were strongly correlated (r=0.874, P<0.01), the effects of migratory distance and migratory restlessness were independently exam-

Number of autumn/winter records of continental vagrants in Japan. ined to avoid multicollinearity. The first ANCOVA was conducted by using the number of autumn/ Scientific name winter records as a dependent variable. Independent Lanius collurio Lanius isabellinus Phylloscopus trochilus Phylloscopus collybita Phylloscopus sibilatrix atrogularis Turdus ruficollis Turdus pilaris Turdus iliacus Turdus viscivorus Turdus Anthus pratensis Anthus trivialis Anthus roseatus

Table 2. variables were migratory distance, distance from the

86 Vagrant continental passerines in Japan

Table 3. Pearson’s correlation coefficients between the quantitative variables.

Distance from normal Migratory Distribution size Migratory distance distribution range restlessness Autumn/winter records 0.501** −0.134 0.624** 0.721** Distribution size −0.138 0.404** 0.448** Distance from normal distribution range 0.080 −0.269* Migratory distance 0.874**

*: P<0.05, **: P<0.01.

Table 4. Summary statistics for the ANCOVA analyses of the number of autumn/winter records.

Independent variable df F P Migratory distance 1 24.715 0.000 Distribution size 1 3.574 0.065 Distance from normal distribution range 1 0.543 0.465 Migratory direction 8 0.472 0.869 Genus 3 1.315 0.282 Migratory direction* Genus 13 0.651 0.798

Independent variable df F P Migratory restlessness 1 40.865 0.000 Distribution size 1 2.472 0.123 Distance from normal distribution range 1 1.846 0.181 Migratory direction 8 0.497 0.851 Genus 3 1.139 0.344 Migratory direction* Genus 13 0.821 0.636

normal distributional range, normal distribution size, distribution range: F1, 43=0.54, P=0.47; migratory migratory direction, and genus. The second ANCOVA direction: F8, 43=0.47, P=0.87; genus: F3, 43=1.32, was conducted by replacing migratory distance with P=0.28). The interaction effect of migratory direc- migratory restlessness as an independent variable. tion and genus was not significant (F13, 43=0.65, All analyses, including calculation of Pearson’s cor- P=0.80) (Table 4). relation coefficients and ANCOVA, were conducted The results of the second ANCOVA revealed a using SPSS ver. 21 (IBM Corp 2012). For both the significant positive effect of migratory restlessness ANCOVAs, Levene’s test of equality of error vari- (F1, 43=40.87, P<0.001). The effects of the remain- ances indicated that the relationship between the ing independent variables were not significant dependent and independent variables did not differ (normal distribution size: F1, 43=2.47, P=0.12; dis- significantly as a function of the independent vari- tance from normal distribution range: F1, 43=1.85, ables. P=0.18; migratory direction: F8, 43=0.50, P=0.85; genus: F3, 43=1.14, P=0.34). The interaction effect RESULTS of migratory direction and genus was not significant (F13, 43=0.82, P=0.64) (Table 4). The results of the first ANCOVA revealed a significant positive effect of migratory distance DISCUSSION (F1, 43=24.72, P<0.001). The effects of the remaining variables were not significant, although normal distri- To the best of my knowledge, the present study bution size showed a marginally significant positive is the first to undertake a scientific evaluation of the effect (F1, 43=3.57, P=0.065; distance from normal factors influencing the occurrence of avian vagrants

87 Y. UMEGAKI in Japan. The occurrence of continental vagrant kept in mind that direction may differ dramatically, passerines in Japan was previously thought to be even within the same species. For example, subpopu- affected by the vicinity of their regular distributional lations of the Eurasian Blackcap Sylvia atricapilla ranges. Consequently, there was no clear explanation use completely different migratory routes in autumn, for the regular occurrence of species from distant with individuals from central Europe moving south- locations (Ikenaga et al. 2012; Young Guns 2014). west and individuals from eastern Europe moving In some cases, this phenomenon was even thought southeast (Berthold 1988). Further research should to originate from the escape of caged birds (Birder consider migratory direction at the subpopulation Henshubu 1999; Ikenaga et al. 2012). The results of level, if possible, or at least be aware of the variety this study indicate that the occurrence of vagrants of directions within the same species. is predicted by migratory distance, rather than the Compared to previous findings (Pfeifer et al. 2007), distance between the normal distributional range and the positive effect of distribution size was only mar- Japan, which is consistent with previous studies con- ginally significant. There may be various interpre- ducted in Western European countries (Thorup 2004; tations to account for this difference; however, the Pfeifer et al. 2007). Among the independent variables results of the analyses conducted in the present study examined, migratory restlessness showed the stron- depend on the data used. On the basis of the specified gest positive effect on the occurrence of continental criteria for selecting the species used in this study, I vagrants. This effect was significant, even when the included non-recorded species with wide distribu- effects of other variables were controlled, as shown tion ranges, e.g., the Southern Grey Shrike Lanius by Pfeifer et al. (2007). Therefore, hypothesis 2 was meridionalis, and excluded recorded species with supported. The positive effect of migratory restless- wide distribution ranges, e.g., the Water Pipit Anthus ness on the occurrence of vagrants strongly indicates spinoletta. The operational definition of continental that the movement of continental vagrants to Japan vagrants may have contributed to the less pronounced is affected by a navigational error in the endogenous effect of distributional size. Furthermore, observer migratory program of individuals, as only birds that coverage is considerably lower in Japan compared are sufficiently restless arrive in Japan. with northwest Europe, resulting in limited records The present findings support the fact that Japan of vagrants. has more vagrants from the Western Palearctic than The present study has a number of limitations. from Taiwan, China, or Mongolia. Although located First, this study does not explicitly test the reverse at a distance of approximately 111 km, very few orientation hypothesis. Thus, it cannot be concluded Taiwanese birds have been recorded in Japan. Even whether the occurrence of continental vagrants the commonest Taiwanese birds, e.g., the Black is explained by reverse orientation. However, the Bulbul Hypsipetes leucocephalus and the Bronzed results have a number of implications. Logically, Drongo Dicrurus aeneus, have not been recorded, reverse orientation does not explain the occurrence probably due to their high level of residency. of some of the investigated species, because their Migratory direction did not significantly predict vagrancy shadow does not cover Japan (e.g., Siberian the abundance of vagrants; thus, hypothesis 1 was Chiffchaff Phylloscopus collybita tristis). In com- only partially supported. This discrepancy may be parison, the vagrancy shadow of the Wood Warbler because many birds primarily migrate in a south- includes the northern half of Japan, which is the only ward direction to wintering areas in the northern area where this species has been recorded. This phe- hemisphere, whether recorded in Japan or not, with nomenon may indicate different degrees of reverse little variation to the west. In addition, Thorup (2004) orientation among migratory species, even for those only considered the species that have been recorded within the same genus (Thorup 2004). However, it in northwest Europe when showing that migratory remains unclear whether the occurrence of conti- direction predicts the occurrence of vagrants. Because nental vagrants in Japan is affected by reverse ori- the current study included non-recorded species in entation, random scatter migration (Gilroy & Lees the analysis, the possibility that migratory direction 2003), or migration toward a certain angle (Berthold does predict the abundance of certain vagrants can- & Terrill 1988). The possible effect of observer cov- not be discounted. Further study with a specific focus erage should also be taken into account. For example, on species recorded in the region is required. When Hegura-jima (Japan), like Fair Isle (Shetland Islands, considering migratory direction, it should also be United Kingdom), attracts many birders. Therefore,

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