Three interesting Brant from Massachusetts

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Note: I’m preparing posts on the range and identification of Brant subspecies, which will help make the following more understandable to those who are not already well-versed in the intricacies of Brant.

Over the last fifteen or so years I have seen several odd “gray-bellied” Brant along the US Atlantic coast. This spring I finally made a small effort to study Brant identification, and even though I have only been able to examine a few hundred Brant closely, I’ve seen at least five birds (and photographed three) that stand out from the standard Pale-bellied Brant that are expected here.

Mystery Brant 1 - Typical Pale-bellied Brant (left) and slightly darker gray-bellied Brant (right). This is a composite photo, but these two birds were less than ten feet apart and the photos were taken seconds apart, so the comparison of colors is accurate. The slightly darker-bellied bird also had a slightly darker back. The almost absent white necklace on the Mystery Brant is a variation shown by at least 10% of Pale-bellied Brant. Photo 8 Feb 2011, Boston, MA; copyright David Sibley.

The first was a slightly darker bird (photo above) that I would not have noticed without being very attentive to subtle differences. It could be the dark extreme of “normal” variation in Pale-bellied Brant (B. b. hrota), but it stands apart from all of the several hundred Pale-bellied Brant I’ve studied this spring. If we assume it is dark-bellied because of mixed parentage, then it could be an intergrade with either Black Brant (B. b. nigricans from western Canada) or Dark-bellied Brant (B. b. bernicla from Siberia). In favor of Black Brant is the slightly darker back and fairly clean white flanks. In favor of Dark-bellied is the fact that pure Black Brant has a much more prominent necklace, and one could argue that the white flanks are invaded by more gray than is typical on Pale-bellied, suggesting Dark-bellied parentage. Either way, it’s probably a backcross with Pale-bellied, since the intermediate features are so weak, and it’s probably unidentifiable, but I’ll speculate that it’s something like a Black x Pale-bellied intergrade back-crossed with Pale-bellied.

Mystery Brant 2 (right) - Pale-bellied Brant (left) and slightly darker gray-bellied Brant (right) tipping up to feed on eel-grass. 10 April 2011, Nahant MA. Photo from video copyright David Sibley.

The next bird was another gray-bellied adult swimming with Pale-bellied Brant (above). I noticed it when the birds tipped up to feed, and it was distinctly darker gray on the belly than any of the Pale-bellied Brant present, which were all very pale gray (nearly white) on the belly.

Mystery Brant 2 (right) - Pale-bellied Brant (left) with the same darker gray-bellied bird from the photo above. 10 Apr 2011, Nahant, MA. Photo from video copyright David Sibley.

Overall this second mystery Brant is very similar to Pale-bellied, but two things stand out besides the gray belly. The back is about the same color as the Pale-bellied Brant nearby, if anything slightly paler, and definitely not darker. The flanks are extensively mottled with gray, not as white or as sparsely-marked as the Pale-bellied Brant. Both of these features (and the unremarkable white necklace) suggest that this bird is part Dark-bellied Brant (B. b. bernicla) rather than part Black Brant. I don’t think the belly is dark enough, or the flanks gray enough, for this to be a pure Dark-bellied, but I propose that this is a Pale-bellied x Dark-bellied intergrade.

Mystery Brant 3 - A very dark-bellied Brant tipping up to feed. 10 April 2011, Nahant MA. Photo from video, copyright David Sibley.

The third mystery Brant (above) was also detected as it tipped up to feed, revealing a dark gray belly even darker than on Mystery Brant 2, as well as a contrasting dark band bordering the rear edge of the flanks.

Mystery Brant 3 - A very dark Brant showing dark breast sides, white flanks, and dark back. 10 April 2011, Nahant MA. Photo from video, copyright David Sibley.

This bird was more obvious than Mystery Brant 2 when swimming. It shows a very dark and very brownish back. At many angles there is no visible contrast between the black neck and dark back. The dark gray-brown sides show relatively little contrast with the black breast, but the flanks are as white as any Pale-bellied. This all looks good for a pure Black Brant (B. b. nigricans) but the white necklace is broken on the front of the neck, and the belly color may be a bit on the pale side. I propose that this bird is a Black x Pale-bellied intergrade.

Any of these three could be the enigmatic Western High Arctic Gray-bellied Brant (subspecies unassigned), which nests on Melville Island in far northwest Canada and winters mainly in Puget Sound. I have no personal experience with Gray-bellied Brant, but based on what I’ve read I think Mystery Brant 1 is the best prospect for Gray-bellied. Unfortunately the Gray-bellied Brant is very similar to Pale-bellied, and some paler individuals may be indistinguishable from Pale-bellied. It seems likely, then, that most Gray-bellied Brant would look essentially identical to some Pale-bellied x Black Brant intergrades. In addition, since Gray-bellied itself probably interbreeds with both Pale-bellied and Black, there must be a “stew” of confusing and unidentifiable intermediate Brant coming from northwestern Canada.

Clearly there is a lot to learn about Brant in the US. The common wintering Pale-bellied birds in the east are very consistent in belly color, and any individual showing a distinctly darker gray belly (even if only slightly) can be assumed to have some mixed parentage. These gray-bellied Brant are a fascinating puzzle, and any careful observer can add to our understanding and help move closer to solving the puzzle.

2 thoughts on “Three interesting Brant from Massachusetts”

  1. Dear David,
    Most interesting. I wish I had some relevant experience to share, but any Brant is rare in Texas, and it’s been more than 20 years since I used to see Pale-bellieds regularly on my local patch in southern England.
    However i will provide this link to some birds from Barrow, Alaska, as one of them looks like a possible hybrid (or even Melville Island type?); note especially the weak neck collar on a non-juvenile bird:
    http://www.martinreid.com/Main%20website/brant.html
    Regards,
    Martin

    1. Hi Martin, Thanks for the link. That’s definitely not a Black Brant, as you know. Geography favors the Western High Arctic (Melville Island/Gray-bellied) form rather than a vagrant Pale-bellied from the east, and the belly looks a little dark for a true Pale-bellied, but it’s hard to say for sure and that wouldn’t rule out an intergrade. On the other hand there is a lot of molt movement in late summer around the Arctic, and it’s conceivable that some Pale-bellied Brant from eastern Canada could head west to molt in Alaska, then migrate back east for the winter.

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