Late Sunday afternoon (5 Jan), Patricia Lindsay and I studied a very
distinctive dark Brant at Pt Lookout, Nassau County, Long Island. The
bird was among a large flock on the flat immediately east of Lido
Boulevard, but all the birds were flushed in short order by a
dog-walker.
Clearly not an example of the locally abundant subspecies hrota
("Atlantic" or "Pale-bellied"), this bird also differed in multiple
respects from Pacific Black Brant (orientalis):
-Its overall dorsal plumage tone was very slightly, if at all, darker
than that of accompanying hrota (vs. obviously darker, as in Black
Brant)
-Its dark ventral apron extended less far rearward and blended diffusely
with its white lower belly (rather than forming an obvious, abrupt
dividing line posterior to the legs, as in Black Brant)
-Its ventral neck collar was only slightly bolder than that of adult
hrota nearby, lacked well-defined webbing, and was incomplete ventrally
(vs. broad and ventrally complete, with bold webbing, as in Black
Brant).
Photos showing these features can be seen here:
https://picasaweb.google.com/109808209543611018404/LongIslandMiscellany2014
Birds of this appearance have puzzled ornithologists for more than a
century and a half, beginning with a specimen collected in New Jersey in
1846, and continuing with a sparse but consistent accumulation of
records from the east coast of North America and elsewhere. Because
their appearance is in various ways intermediate between Atlantic
Pale-bellied and Pacific Black Brant, they have been suspected as
hybrids--although no direct evidence supports this view. Alternatively,
these birds' close resemblance to the population breeding in the western
Canadian High Arctic, known as Gray-bellied Brant, suggests that they
might be vagrants rather than hybrids.
It is a signature feature of this conundrum that the identity of the
1846 NJ specimen is itself controversial. Published by Lawrence as the
type of a new taxon, nigricans, it was regarded for a century as the
type for Pacific Black Brant, but it was distinguished from that taxon
by Delacour and Zimmer (1952). P. A. Buckley and I (2002) documented the
congruence among this specimen, other eastern North American records,
and Gray-bellied Brant, and proposed that the name nigricans be
restricted to Gray-bellied Brant (previously not formally named).
Shai Mitra & Patricia Lindsay
Bay Shore, NY
Delacour and Zimmer (1952): https://sora.unm.edu/node/20044
Three geese resembling Gray-bellied Brant/Lawrence's Brant from Long
Island, New York. 2002, Buckley, P.A.; Mitra, S.S. North American Birds,
56: 502 - 507.
Abstract available online here:
http://pubs.er.usgs.gov/publication/5224228
BNA account (Lewis et al. 2013):
http://bna.birds.cornell.edu/bna/species/337/articles/systematics
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