SPECIES SPLIT (proposal)
Bean Goose Anser fabalis
Since the mid 1800s, two morphologically and ecologically divergent groups of bean beese
have been recognised in Europe: a northern, tundra-breeding group that winters on arable
land (rossicus) and a southern, taiga-breeding group wintering on moorlands and meadows
(fabalis) (Naumann 1842, Berry 1938, Coombes 1951, Huyskens 1977, 1979, van Impe
1980a, 1980b, van den Bergh 1985, Burgers et al. 1991). In addition to differences in their
summer and winter habitats, tundra and taiga bean geese also differ in average size and
proportions (greater body size, longer neck, longer wings, more slender bill with straight
lower mandible in fabalis; smaller body size, shorter neck and wings, shorter bill with curved
lower mandible in rossicus; Coombes 1951, Roselaar 1977, Burgers et al. 1991), the
frequency distribution of bill colour and pattern (in fabalis yellow bills are commonest and
dark bills infrequent; in rossicus dark bills predominate and yellow bills are almost non-
existent; van Impe 1980a, Burgers et al. 1991), vocalizations (more acute in rossicus,
resembling A. brachyrhynchus; Coombes 1951, Barthel 1995), diet (fabalis feeds on grasses
whereas rossicus mostly feeds on bulbs; van Impe 1980b), photosensitivity (nocturnal
feeding observed in fabalis but absent in rossicus; van Impe 1980b), activity pattern (fabalis
arrives earlier on feeding grounds and departs later than rossicus; van Impe 1980b), and
behaviour (fabalis always drinks fresh water, rossicus predominantly drinks brackish water;
van Impe 1980b). In eastern Asia, tundra (serrirostris) and taiga (middendorffii) bean geese
seem to differ in the same way as their European counterparts, showing differences in
proportions (Roselaar 1977), vocalizations, habitat preferences and phenology (Yokota et al.
1982, Miyabayashi et al. 1994).
Phylogenetic analysis of mitochondrial DNA sequences found no overlap of
haplotypes between fabalis and rossicus/serrirostris, but could not differentiate rossicus from
serrirostris (Ruokonen et al. 2008). Phylogenetic analysis of nuclear DNA sequences (41,736
exons, representing 5887 genes) provides evidence that Tundra Bean Goose (rossicus) is
more closely related to Pink-footed Goose A. brachyrhynchus than to Taiga Bean Goose
(fabalis) (Ottenburghs et al. 2016). A more recent phylogenomic analysis, based on fixed or
nearly-fixed nuclear differences between the taxa, found that Taiga Bean Goose (fabalis)
was more closely related to Pink-footed Goose than to Tundra Bean Goose (rossicus).
These findings are inconsistent with continued treatment of Tundra Bean Goose as a
subspecies of A. fabalis. Further genomic comparisons have shown that Taiga and Tundra
Bean Geese can be reliably separated by their genomes, despite evidence for past gene flow
(Ottenburghs et al. 2020).
Suggestions that Taiga and Tundra Bean Geese intergrade (e.g. Delacour 1951)
were based on a typological view, according to which yellow-billed birds were regarded as
pure fabalis, black-billed birds as pure rossicus, and all intermediate phenotypes as
‘intergrades’ (Sangster & Oreel 1996). Study of museum specimens and live birds shows that
morphological variation is bimodal (Coombes 1951, Burgers et al. 1991) ruling out the
hypotheses that Taiga and Tundra Bean Goose are just endpoints of clinal variation (Hartert
1915) or that these taxa are connected by broad intergradation zones (Delacour 1951).
Pair formation in arctic wildfowl occurs on the wintering grounds. In winter, Taiga and
Tundra Bean Goose are mostly segregated by habitat (Huyskens 1977, 1983, van Impe
1980b) which prevents formation of mixed pairs. Nevertheless, these taxa are frequently in
contact, but direct observations indicate no interaction (Ouweneel 1979). Importantly, ringing
recoveries during the breeding season of Taiga and Tundra Bean Goose trapped in winter in
Western Europe are from non-overlapping areas in Siberia, indicating that they possess
allopatric or parapatric breeding ranges and that mixed pair formation must be rare at most
(Sangster & Oreel 1996).
East Asian middendorffii forms a separate lineage from fabalis and
rossicus/serrirostris in a mitochondrial gene tree and is sister to other bean geese (Ruokonen
et al. 2008). However, these DNA sequences represent a single marker, there is a wide
geographic gap between sampling localities of breeding fabalis and breeding middendorffii in
central Russia that makes interpretation of taxonomic boundaries difficult, and morphological
variation of fabalis and middendorffii is clinal (Roselaar 1977). MtDNA haplotypes typical of
fabalis and middendorffii were both obtained from Tomsk Oblast but the identity of all these
individuals could not be ascertained by morphology (Ruokonen et al. 2008); the fabalis were
sampled in early May and may have been migrants. We believe there is insufficient evidence
to regard middendorffii as a full species and that further study of middendorffii (its
phylogenetic position and its interaction with fabalis) is warranted.
The putative subspecies A. f. johanseni was described by Delacour (1951) from a
small number of specimens collected on the wintering grounds in China. This name was
arbitrarily assigned to a breeding population located geographically between fabalis and
middendorffii (i.e. east of the Urals). However, fabalis wintering in the Netherlands recovered
from this area included both yellow-billed and black-billed birds (Burgers et al. 1991). This is
evidence that A. f. johanseni, characterized by its black bill, represents a morphological type,
rather than a separate population. Thus, the name johanseni is best considered a synonym
of fabalis (Sangster & Oreel 1996).
Concordant differences in morphology, ecology, behaviour and mitochondrial and
genomic DNA, in combination with evidence for reproductive isolation and phylogenomic
support for a non-sister relationship provide strong evidence that Taiga and Tundra Bean
Geese represent distinct lineages that are best treated as species:
Taiga Bean Goose Anser fabalis (polytypic, with subspecies fabalis and tentatively
middendorffii)
Tundra Bean Goose Anser serrirostris (polytypic, with subspecies rossicus, serrirostris)
Barthel, P.H. 1995. Identification des oies grises du genre Anser. Ornithos 2: 27–41. [In
French.]
Berry, J. 1938. Some taxonomic problems presented by geese of the type Anser fabalis.
Proc. Int. Ornithol. Congr. 8: 339–344.
Burgers, J., Smit, J.J. & van der Voet, H. 1991. Origins and systematics of two types of the
Bean Goose Anser fabalis (Latham, 1787) wintering in the Netherlands. Ardea 79:
307–316.
Coombes, R.A.H. 1951. Two races of Bean Goose Anser arvensis in Western Europe. Proc.
Int. Ornithol. Congr. 10: 185–188.
Delacour, J. 1951. Taxonomic notes on the Bean Geese, Anser fabalis Latham. Ardea 39:
135–142.
Hartert, E. 1915. Die Vögel der Paläarktischen Fauna 2. R. Friedländer & Sohn, Berlin.
Huyskens, G. 1977. De verspreiding van Anser fabalis fabalis en Anser fabalis rossicus in
Europa buiten het broedseizoen. Watervogels 2: 69–75. [In Dutch.]
Huyskens, G. 1979. De Europese Rietganzen A. fabalis fabalis en A. fabalis rossicus-
ondersoorten of soorten? al of niet schadelijk? Mens en Vogel 17: 204–208. [In Dutch.]
Huyskens, G. 1983. De veldkenmerken van de Taigarietgans Anser fabalis fabalis en de
Toendrarietgans Anser fabalis rossicus. Wielewaal 49: 257–275. [In Dutch.]
Miyabayashi, Y., Sugawa, H. & Kurechi, M. 1994. Inventory of goose habitat in Japan:
compilation of the inventory and conservation issues identified. Pp. 35–65 in
Miyabayashi, Y. (ed.). Inventory of goose habitat in Japan. Japanese Association for
Wild Geese Protection, Wakayanagi, Japan.
Naumann, J.F. 1842. Vögel Deutschlands. Band XI. Leipzig.
Ottenburghs, J., Honka, J., Müskens, G.J. & Ellegren, H. 2020. Recent introgression
between Taiga Bean Goose and Tundra Bean Goose results in a largely homogeneous
landscape of genetic differentiation. Heredity 125: 73–84.
Ottenburghs, J., Honka, J., Heikkinen, M. E., Madsen, J., Müskens, G.J. & Ellegren, H.
- Highly differentiated loci resolve phylogenetic relationships in the Bean Goose
complex. BMC Ecology and Evolution 23(1), 2.
Ottenburghs, J., Megens, H.-J., Kraus, R.H.S., Madsen, O., van Hooft, P., van Wieren,
S.E., Crooijmans, R.P.M.A., Ydenberg, R.C., Groenen, M.A.M. & Prins, H.H.T. 2016.
A tree of geese: a phylogenomic perspective on the evolutionary history of true geese.
Mol. Phylogenet. Evol. 101: 303–313.
