BASIC PRINCIPLES
Autumn migration is so often characterised by one family: thrushes. The tseep of Redwings overhead in clear October skies, and hulking Fieldfares
chacking as they arrive noisily from a North Sea crossing often harbour highly prized, mouth-watering rarities from the east that are eagerly sought by rarity-hunters from Scilly to Shetland (see pages 22-25).
But it is also at this time of year that British and
Irish birders may encounter thrushes from North America – namely the elusive, Song Thrush-eseque Catharus thrushes. Subtle in nature, they can offer a bit more of an identification headache than their Old World cousins. Four of the five species have been recorded in Britain and Ireland, while another, similar thrush from another genus,
Hylocichla – Wood Thrush – has also been recorded in Britain and is included for completeness.
Catharus thrushes are small and typically shy and retiring, often remaining hidden in woodland glades or thickets rather than parading out in open furrows. Occasionally, though, tired vagrants can be less furtive and even downright showy.
Song Thrush, the benchmark comparison when it comes to identification, has a subtly more variegated face pattern with mealy, dark-bordered ear coverts, a thin eyering and more obviously spotted underparts that extend with consistent intensity further onto the lower belly and flanks.
It is also larger than the five American thrushes, significantly so in the case of the Catharus species.
Vagrancy potential
Note that Bicknell’s Thrush, a fifth species of Catharus, has not yet been recorded in Europe and is not safely separated in the field from Grey-cheeked, thus is not covered here.
All five species of Catharus thrush are, for the most part, nocturnal migrants. Swainson’s and Grey-cheeked are long-distant migrants and thus are the more expected vagrants in Europe.
Veery is also a relatively long-distance migrant, but with a slightly more southerly distribution, as well as an earlier migration, it is one of the lesser-recorded Catharus in Europe.
Hermit Thrush has a more northerly distribution and leaves its breeding grounds later than other Catharus thrushes, but compared with Grey-cheeked and Swainson’s, it is a shorter-distance migrant and thus is likely to be encountered less frequently in Europe.
With a single British record and three from the Azores, plus a bird found dead in Iceland, Wood Thrush remains exceedingly rare in Europe – presumably a result of its more southerly breeding range and earlier migration out of north-eastern USA.
Grey-cheeked Thrush
Breeds from northern Alaska across northern Canada to Newfoundland south to central Quebec, with peak migration dates in New York from 14-28 September. It is a small thrush with uniform, cold grey-brown upperparts and tail; many show a purer grey wash to the ear coverts that contrast with a brighter yellow base to the mandible. Unlike other Catharus thrushes, it lacks a conspicuous eyering, but be aware some individuals can show a paler area around the eye, though this is often diffuse, and not well defined as in Hermit or Swainson’s Thrushes. The streaked malar blends into a clean, dark-spotted upper breast overlain with a warmer buff suffusion that fades into pale greyish flanks.
Separation of Grey-cheeked and Bicknell’s is compounded by Newfoundland-breeding Grey-cheeked being described as intermediate between the two species (Sibley 2000). The ranges are allopatric, with Grey-cheeked breeding farther north and wintering farther south than Bicknell’s.
Swainson’s Thrush
Breeds from northern Alaska across northern Canada to Newfoundland and, in the east, south to northern New England. Autumn migration of eastern populations is mostly along the Atlantic coast and peaks between 1 September and 15 October.
At first glance it is more likely to be confused with the larger and more heavily spotted Song Thrush, rather than Grey-cheeked, due to its more contrasting pattern of pale lores and buff eyering, giving a ‘spectacled’ or ‘surprised’ look. The overall colour is warm toned, being a swarthy olive-brown above with a noticeable warmer buff wash across the upper breast, ear coverts, lores and eyering. The breast spots are dark blackish-brown and appear slightly coalesced; as with most other Catharus, these are most prominent across the upper breast, fading out towards the flanks.
Hermit Thrush
Breeds from central Alaska east to Newfoundland and south to southern California, northern New Mexico, Wisconsin and Virginia. In the east, migration peaks from late September to mid-October. It is one of last thrushes to leave and is a shorterdistance migrant, wintering from southern New England southward.
This furtive Catharus is very nightingale-like due to its narrow, pale eyering, greytoned brown upperparts and a contrasting rufous tail which is often cocked, but the heavily spotted upper breast rules out a Luscinia.
Compared to other Catharus, Hermit Thrush appears longer legged, with a relatively longer and spikier bill. The upper breast is often paler, lacking the warm buff hues of Swainson’s, making the dark malar and spotting of the upper breast more contrasting and distinct. A Catharus thrush with a combination of pale eyering and a dull rufous tail is a Hermit.
Veery
Breeds from southern
British Columbia east to Newfoundland and south to New Jersey and Georgia, wintering in South America. It migrates earlier than the previous species, peaking in the east between 24 August and 7 September.
The warm, foxy-toned upperparts make nailing a Veery rather straightforward. Like Grey-cheeked, it lacks a prominent eyering. The lower throat is a rich buff, contrasting with the rest of the silky, greyish-white underparts. The dark malar blends into breast spotting that is smaller, more muted and browner than the other species, fading quickly into greyish markings on the lower breast. On weakermarked birds, the upper breast may be almost devoid of any noticeable markings, especially when seen side on. On the ground, Veery often appears to be disproportionately longer
2 Cold plumage tones, lacking a contrasting rufous tail and strong spectacles, point to Grey- cheeked. Side on, this species often appears a uniform olive- grey overall, with a distinct yellowish base to the bill. There is often some lightening around the eye and the most obvious feature is the dark-streaked malar that merges into a dark necklace of spots that fade out, blending into the clean grey- brown flanks. A pale throat and cold buff wash across the lower throat is typical of autumn Grey- cheeked. Bicknell’s would appear similar and is described as warmer coloured and having a more extensive yellow bill base, but this species is not safely separable outside breeding areas.
6 A wellmarked bird, with obvious spots across the breast overlain with a light buff wash. Seen briefly, it could easily be initially mistaken for Song Thrush, but note the uniform pale grey flanks and lack of obvious spotting on the lower half of the underparts. The head pattern on this bird shows less solidly dark ear coverts and a pale grey area around the eye that may be mistaken for an eyering, but note the area is diffuse and whitish, not buff. The lack of an adjoining well- defined buffy loral line eliminates Swainson’s.