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Heavily-marked Male Brewer’s the next early fall, as do all black species of blackbirds occurring in Colorado (see Leukering 2011 concerning Blackbirds Red-winged Blackbird). TONY LEUKERING THE PROBLEM Rusty Blackbird (Euphagus carolinus) occurs in Colorado as a rare wintering species on the East Slope While the typical fresh basic plumage (fall into winter) of the state, primarily from the eastern foothill edge of male Brewer’s Blackbird does not differ dramatically and east. Fall and spring migration records extend the from worn basic plumage (spring, summer), there is typical occurrence period from mid-October through sufficient variation in the width and coloration of the early April (eBird 2020). Because of the species’ scarcity pale fringes on many head and upperparts feathers on in the state, it is sought by many of the state’s birders, males as to suggest caution in using plumage coloration many of whom have little experience with it. Brewer’s to distinguish them from male Rusty Blackbirds. In Blackbird (Euphagus cyanocephalus) is very similar some male Brewer’s, the colored feather fringes are not to Rusty Blackbird but is a common breeding species only wider, but warmer-colored, with some sporting an and uncommon wintering species in Colorado. Eye orangish color not significantly different from the rusty color helps greatly in distinguishing females of the fringes of male Rusty Blackbirds. two species – yellow-white in Rusty, dark in Brewer’s. THE SOLUTION The occasional female Brewer’s Blackbird exhibits pale eyes (McKee and Jaramillo 1999), so caution is Please refer to the photos of male Rusty Blackbird (Fig. warranted in using eye color as the sole identification 1; top) and male Brewer’s Blackbird (Fig. 2; bottom). Note character of female Rusty Blackbirds. Males of both that the two photos were captured only a day apart in Euphagus species have very similar pale eyes, and the same year, minimizing any temporal difference in many birders rely on the color and pattern of fresh wear between the two birds. basic plumage (see Leukering 2010 for plumage terminology) in distinguishing male Rusty Blackbirds While only a tiny percentage of male Brewer’s from male Brewer’s Blackbirds in Colorado. Blackbirds sport feather fringes that approach the bright rusty color of Rusty Blackbird feather fringes, In late summer and early fall, adults and juveniles of quite a few have warmer-colored fringes than is typical both Rusty and Brewer’s blackbirds conduct a molt of the species. The Brewer’s Blackbird depicted in that replaces all (definitive prebasic molt in adults; see Fig. 2 has more-extensive tipping and fringing than is Leukering 2010) or virtually all (preformative molt in typical of the species, particularly for so late in the juveniles) of their previous feather sets. Most of the plumage year (February). While this bird’s fringes are individual feathers of this new plumage of male Rusty fairly dull, they do approach orange, particularly on Blackbirds are tipped or fringed with rusty-orange, a the crown and back. It is easy to imagine that if this facet resulting in the species’ English name. Those rusty bird were among a few other male Brewer’s Blackbirds fringes begin wearing immediately and, depending with more-typical plumage for February, it could cause upon the width of those fringes, the individual feathers an elevated heartbeat. In fact, this individual even become entirely dark sometime between January and has fringes on most of the wing feathers, contra the May, inclusive. statement in at least some editions of the National Geographic Society Field Guide to the Birds of North Male Brewer’s Blackbirds typically have more-subdued America (National Geographic Society [NGS] various fringes to their new feathers, with those fringes years): “A few fall males show rusty feather edgings, generally being narrower and, particularly, duller, but never as rusty as in Rusty Blackbird and never on being brown or gray-brown (T. Leukering pers. obs.). tertials or wing coverts.” As in most aspects of biology, An additional difference between the males of the one can get into trouble using words such as “always” two species is that Brewer’s Blackbirds only rarely have and “never,” as organisms are often more-variable than paler fringes to feathers on the wings, which results in a we understand, and most of them do not read the stronger wing-to-back color contrast in fresh plumage. printed word. Neither species has a prealternate molt, thus adults wear only a single set of feathers from early fall until

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Figure 1. This Euphagus with very wide and very orange fringes on the upperparts feathers can be easily and safely identified as a Rusty Blackbird. Late in winter, however, when fringes have mostly worn off and male Rusty Blackbirds are mostly black, distinguishing the two Euphagus species gets more problematic. Note this Rusty Blackbird’s relatively short tail as compared to that of the Brewer’s Blackbird, below. Barr Lake State Park, Adams County, Colorado; 11 February 2014. Photo by Loch Kilpatrick.

Figure 2. This heavily-marked male Brewer’s Blackbird illustrates the problem with identifying Rusty Blackbirds solely on the presence of wide, paler feather fringes. To be certain of a Euphagus identification, check out the tail length, which on this Brewer’s is notably long; compare it to the tail length of the Rusty Blackbird, above. Laytonville, Mendocino County, California; 12 February 2014. Photo by Giff Beaton.

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While the letter of the above NGS quote is incorrect, LITERATURE CITED the spirit is right, given that all else is equal, such as beginning width of fringes and wear rate of fringes. eBird. 2020. eBird: An online database of bird Unfortunately, in biology, only very rarely is all else distribution and abundance [web application]. eBird, actually equal. The tips or fringes on wing feathers Ithaca, New York. Available: http://www.ebird.org. such as tertials and wing coverts of Rusty Blackbird are (Accessed: 1 August 2020). typically wider, particularly on the tertials, than that shown by the bird in Fig. 2. However, some late-season Leukering, T. 2010. Molt and plumage: A primer. male Rusty Blackbirds (https://tinyurl.com/RUBL- Colorado Birds 44:135-142. https://cobirds.org/CFO/ Feb-male) sport fringes that are similarly insignificant; ColoradoBirds/InTheScope/24.pdf particularly note the nearly invisible rusty tertial tips Leukering, T. 2011. Spring plumage change in passerines: on the male Rusty in the linked photo and compare Prealternate molt vs. wear. Colorado Birds 45:154-157. them to the obvious fringes on some of the tertials https://cobirds.org/Publications/ColoradoBirds/ on the Rusty in Fig. 1. Of course, on the bird in the InTheScope/20.pdf linked photo, the back feathers still sport very orange and very wide fringes, making that bird’s identification McKee, B. and A. Jaramillo. 1999. Variation in iris color straightforward. of female Brewer’s Blackbirds. Western Birds 30:131-132. The solution is to study the whole bird, particularly National Geographic Society. 1999. Field Guide to the various shape aspects. Of course, that is the solution Birds of North America, 2nd Edition, Washington, D.C., to every identification quandary. Perhaps the single National Geographic. best distinguishing feature in this conundrum is tail length, as, except during molt, tail length is always Pyle, P. 1997. Identification Guide to North American reliable. Brewer’s Blackbirds have noticeably long Birds, part I (pp. 637-638). Slate Creek Press, Bolinas, CA. tails, hence the frequent identification confusion with Tony Leukering, 771 Hidden Valley Ct., Fairborn, OH Common Grackle. Rusty Blackbirds have unremarkable 45324 ([email protected]) tails, being similar in proportion to body length to that of Red-winged Blackbird (K. Mihm Dunning, pers. comm.). Given the similarity in overall length of Rusty and Brewer’s blackbirds, the distinctively longer tail of Brewer’s (92-118 mm; Pyle 1997) as compared to that of Rusty (77-96 mm; Pyle 1997) should be quite noticeable. Another very helpful feature, when present, is the obvious pale supercilia, often yellowish, of many male Rusty Blackbirds. The small number of male Brewer’s Blackbirds that sport pale supercilia have those supercilia much less distinct and of generally dull gray color (see https://tinyurl.com/BRBLsuper). Other features that can be useful in distinguishing the two species include the smaller, rounder head of Brewer’s and the longer, thinner bill of Rusty, though bill-length differences are small (6.0-6.9 mm bill depth at tip of nostrils in male Rusty versus 6.7-7.9 mm in male Brewer’s [Pyle 1997]). ACKNOWLEDGMENTS

I greatly appreciate the review of a draft of this essay by Kathy Mihm Dunning.

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