“Black-backed” American Robins

Hi there,

This morning (7 April 2016) I spent several hours investigating American Robins (Turdus migratorius) at the Canadian Museum of Nature collections in Gatineau, Quebec. After reviewing 90-100 adult males from northern Ontario,  central and northern Quebec, and Newfoundland and Labrador, it became clear, even in this modest sample, that blackish tones throughout the upperparts, rich cinnamon tones throughout the underparts and heavily-streaked throats can manifest anywhere throughout a very wide swath of boreal forest stemming from coastal Labrador to eastern and southern James Bay. Compared to ‘typical’ southern Ontario* (James 1991) breeding T. m. migratorius,  birds from the southern and eastern areas of James Bay averaged a sootier base color to their upperparts and a greater extent of blackish tones extending down from the head onto the mantle (see Figure 1). These birds also averaged broader, more coalesced black streaks to the throat and deeper cinnamon tones to their underparts. Central, and especially northern, Quebec birds approached ‘classic’, well-marked T. m. nigrideus birds in both the extent of blackish tones to to the upperparts (denser and extending farther down the back) and cinnamon tones to the underparts. Interestingly, these birds, like those from Labrador, had a very slight cold, grayish suffusion to their upperparts (vs. an average of duskier and sootier in the birds in and around James Bay). The head to some of these birds, especially from the Schefferville and Fort Chimo area, was truly jet black and the throat streaking averaged broader and more coalesced than even the southern and eastern James Bay birds. These birds, like those from the Labrador peninsula, were examples of the extreme expression of the high-northeastern, blackish ‘type.’

In my opinion, clinal and natural variation obscure subspecific assignment of out-of-the-ordinary birds seen during migration. If/when tempted to assign a darkish presumed migrant among ‘typical’ ones, a cautionary prefix such as “possible” is essential (which, before today’s study, I did not fully believe was required). Here I provide a faint, amateurish echo to what Rand (1948) states in his findings re: bird species which provide examples of continuous individual variation. What I also found fascinating is that across the entire span of seemingly endless swath of boreal forest from James Bay east to the Labrador peninsula, birds typical of T. m. nigrideus can be observed (see Figure 2). Interestingly, birds typical of southern Ontario T. m. migratorius can also be found breeding in the high-northeast; this is true of even Labrador peninsula breeders. I did not observe breeding birds from southern Ontario which approached ‘classic’ T. m. nigrideus in appearance; however, I encountered moderately-marked T. m. migratorius which comfortably overlapped in plumage with weakly-marked breeding birds from Newfoundland and Labrador.

(Scratches head)…

I reviewed other subspecific features of purported note, such as the extent of white to the outer retricies (Aldrich & James 1991) but was unable to find consistency in this field mark. Several ‘typical’ T. m. migratorius showed white tail spots larger than richly-marked high northeastern birds; there was a great degree of overlap in this feature in the sample I studied.

Summary

Birds typical of  “Black-backed” American Robins breed throughout northern Ontario, Quebec, Labrador, Newfoundland and also Nova Scotia (northern peninsula?). The combined traits of black back; heavily-marked throat; and rich, cinnamon to the underparts is most common in breeding birds from the humid, high northeast, i.e. Labrador peninsula and this appears to be true of birds from northern and eastern Newfoundland, too, though I was not able to study a great deal of material from this region and as such the above statement involves conjecture.  A truly jet black head and back was only observed in the samples of birds from northeastern Quebec and Labrador; these immensely dark birds represent an extreme expression of the high-northeastern “dark impulse” and do not represent the norm. The norm, I suggest, is represented in this note in the bird at middle in Figure 3. With this all in mind, perhaps as a possible designation, “northern-type” can be assigned to these birds as migrants in the spring and fall. I always take time to study these birds, if/when found, and one thing I look for to aid in a designation is behavior. A dark bird that is loosely associating with other robins and is skittish and wary, more so than the others, even upon distant approach suggests to me possible northern lineage. Consider a bird such as this attempting to nest on a property in hustle-bustle suburbia! In any case, this approach is is pseudo-scientific at best and not in any way endorsed or recommended, most especially if results are uploaded to eBird (or other) as “hard evidence.”

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Figure 1: From left to right: adult male from Northumberland Co., Ontario, collected on 20 April 1984. CMN # 87461. The middle bird is an adult male from east James Bay, Ontario, collected on 29 June 1950. CMN # 37294. The rightmost bird is an adult male from south James Bay, Ontario, collected on 2 July 1960. CMN # 37283.

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Figure 2: At left, adult male from mouth of Moose River, Ontario collected on 16 June 1949. CMN # 36876. At right, adult male from South Brook, Newfoundland, collected on 28 June 1949. CMN # 35091.

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Figure 3: From left to right: adult male from Northumberland Co., Ontario, collected on 20 April 1984. CMN # 87461. The middle bird is an adult male from km 388 along Route de Caniapiscau, Quebec, collected on 22 June 1983. CMN # 80196. The rightmost bird is an adult male from Schefferville, Quebec, collected on 4 July 1977. CMN # 66106.

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Figure 4: Two examples of “Black-backed” American Robins, photographed in the southwest end of Ottawa, Ontario. Each April, I visit a small park near where I live. There is plenty of sumac in this area and the park is surrounded by damp woods with tangles and shrubby undergrowth. I have seen two “Black-backed” here; one on 28 March 2016 (at left above) and the other on 6 April 2015 (at right). Both birds were loosely associating with the other robins in the flock and were extremely skittish while the others could care less that I was standing, partially hidden, within 20 m of them as they foraged.

Ackowledgements

Thank you (once again) to Michel Gosselin of the Canadian Museum of Nature for kindly granting me access to the study skins.

References

Aldrich, J.W. and F.C. James. 1991. Ecogeographic variation in the American Robin (Turdus migratorius). Auk 108: 230–249.

James, R.D. 1991. Annotated Checklist of the Birds of Ontario. Second Edition. Life Sciences Miscellaneous Publications. Royal Ontario Museum, Toronto. *here I follow James’ definition of southern Ontario*

Rand, A.L. 1948. Probability in subspecific identification of single specimens. Auk 65:416-432.

Recommended Reading

Manning, T.H. 1952. Birds of the west James Bay and southern Hudson Bay coasts. Bulletin 125. National Museum of CanadaOttawa.

Todd, W.E.C. 1963. Birds of the Labrador Peninsula and Adjacent Areas. Carnegie Museum, Pittsburgh, Pennsylvania, and the University of Toronto Press, Toronto, Ontario.