Identification of Female Rose-breasted and Black-headed Grosbeaks
(Published in Birding 23:220-223, 1991)
by Joseph Morlan
Although we have progressed in our ability to differentiate female Pheucticus grosbeaks, some individuals still defy field identification. Most field guides emphasize differences in the amount of buff on the breast and head, but many Black-headed Grosbeaks have the underparts and head as white or whiter than those of Rose-breasted Grosbeaks, and Rose-breasted Grosbeak females and immature males frequently have a band of cinnamon or tawny-buff across the breast, especially in fresh fall plumage.
It has been pointed out before (E.g., Jon Dunn [1977]; edited version reprinted in Birding 1978) that the two species have different call-notes. My experience confirms that the main calls are usually separable. The Rose-breasted has a much sharper, more metallic eek as opposed to the Black-headed's lower, harsher kichk. Both species give a whistled phew note (J. Dunn pers. comm.), and fledged juveniles of both give a slurred see-oo note (Bent 1968; Ritchison 1983). The primary songs of both are almost identical (Kroodsma 1974).
Ridgway (1901) and Pyle et al. (1987) detected a difference in the color of the underwing coverts (saffron yellow in Rose-breasted (Figure 4) but clear lemon-yellow in Black-headed). I can see this difference in skins I examined at the California Academy of Sciences, but only in direct comparison. The underwings are difficult to study in the field, and I have sometimes found myself disagreeing with other experienced birders regarding the color of the underwing coverts on some individuals.
The only totally reliable plumage difference is the width of the dark streaks in the middle of the breast, which are consistently thinner on Black-headed Grosbeak. This difference can be best described by likening the streaks on a Black-headed to lines drawn with a sharp pencil, and those on a Rose-breasted to lines painted with a fine brush. (See Pyle et al. [1987] for a nice drawing of this difference.) Claimed differences in flank streaking, however, are not consistent. Black-headed Grosbeaks with the whitest underparts invariably have the finest breast streaking. In many cases, especially in worn summer plumage, these streaks are entirely absent. Thus the palest Black-headeds, those most likely to be misidentified as Rose-breasteds, are actually the most different from Rose-breasted in their breast streaking.
Nevertheless, breast pattern is difficult to assess on many individuals, and direct comparison between the two species is not often possible in the field. I have seen Rose-breasted Grosbeaks with their body feathers fluffed up, obscuring their breast streaks entirely. Such birds could be mistaken for Black-headeds. In the briefly held juvenal plumage, Black-headed Grosbeaks can be more heavily streaked on the breast, with buff confined mostly to the throat. Such birds could easily be mistaken for Rose-breasteds.
While examining photographs, I noticed that female Rose-breasted Grosbeaks invariably had bills that were entirely pale pink or whitish (Figure 1). The bills of the Black-headed Grosbeaks were generally dark gray, especially on the upper mandible. Adult males showed the same difference. Adult male Rose-breasted Grosbeaks had all whitish bills and male Black-headed had dark upper mandibles (Figures 5 & 6). Only one photograph of a Black-headed Grosbeak, an immature male in fall, showed any noticeable pink on its bill. The pink on this individual was almost entirely confined to the lower mandible, with its upper mandible being very dark gray, especially on the culmen.
Bill color on specimens is unreliable because soft-part color changes with time, and none of the specimens I examined had the original bill color noted on their labels. The dark upper mandible was generally apparent on the female Black-headed Grosbeak specimens, however, while the female Rose-breasted Grosbeaks showed uniformly pale bills, suggesting the difference evident in photos.
Over the past several years, I have attempted to test this difference in the field and it seems to work very well. All female Rose-breasted Grosbeaks that I have seen recently had a noticeably pale, often pinkish, upper mandible, while all female Black-headed Grosbeaks had a dark-gray upper mandible.
Probably because bird artists normally use specimens as models, this difference in bill color has been misrepresented in all the standard field guides. Peterson's A Field Guide to Western Birds (1990) shows all Pheucticus Grosbeaks with light bills. The second edition of the National Geographic Society guide (1987) shows the female Rose-breasted with a dark bill, similar to female Black-headed, but has correct bill colors for the males. Birds of North America by Robbins et al. (1983) shows the female Black-headed with a slightly darker bill, but with much less difference than is actually present in life, and the male Black-headed Grosbeak in that guide incorrectly has a decidedly pale bill. Guides illustrated with photographs, such as the Audubon Society Master Guide to Birding (1983) show bill differences correctly as I describe, but no field guide mentions bill color as a field mark in the text.
Most of my attempts to test this proposed character have been in spring and summer. Fall and winter birds may show more variation (Figure 2). Photos and specimens of immature male Rose-breasted Grosbeaks in the fall appear to show fairly dark upper mandibles. Such birds can be identified, however, by their heavy, dark breast streaks, often combined with a tinge of red on the breast, and reddish wing linings (Figure 3). In males of both species, a partial molt in the first spring gives rise to a first alternate plumage similar to the definitive alternate plumage of the adult male but lacking the large white tail spots and retaining brownish flight feathers and usually some brown head striping (Figure 7). Adult males in basic plumage usually resemble males in first alternate plumage but show conspicuous white tail spots and black flight feathers lacking in immatures.
The Rocky Mountain population of Black-headed Grosbeak has been described as a separate subspecies, Pheucticus melanocephalus melanocephalus, in which the male is larger and usually lacks the orange post-ocular stripe of the West Coast race, P. m. maculatus (Bent 1968). I do not know if bill color differs between these two subspecies, and the specimens I examined were not segregated by race.
Occasional hybridization between Black-headed and Rose-breasted grosbeaks in the Great Plains (Anderson and Daugherty 1974, Rising 1983) ensures that some intermediate birds will not be identifiable. If a bird looks more or less intermediate, it is usually best to leave it unidentified.
Further study is needed to determine if bill color can be reliably used to separate females of these two species at all seasons and in all parts of their ranges. I would be interested in hearing from anyone who can confirm or deny the reliability of the differences I propose here.
Acknowledgments
I wish to thank Stephen F. Bailey for access and help with the collection at the California Academy of Science and Jon Dunn, Kenn Kaufman, Paul Lehman and Claudia Wilds for reviewing early drafts of this note.
References
Figure Captions
Figure 1. Typical adult female Rose-breasted Grosbeak, May 1985, Rockport, Texas. The heavy brown streaks in the middle of the breast are diagnostic and the warm buff coloration on the underparts, is typical. Note the striking pink bill.-- B. Schorre/VIREO
Figure 2. Winter female Rose-breasted Grosbeak, January 1971, Magdalina, Columbia. This photograph suggests that fall and winter Rose-breasted Grosbeaks may have darker bills than spring birds. This individual has its upper mandible not quite as dark as typical female Black-headed Grosbeak. Note the broad streaks in the center of the breast are typical of Rose-breasted Grosbeak. -- J. Dunning/VIREO
Figure 3. Immature male Rose-breasted Grosbeak, August 1986, Sawyer County, Wisconsin. Note the blackish, not brown head-stripes, wing-coverts and remiges. Juvenal rectrices have been retained and lack the large white spots found on adults. The heavy breast streaks are an excellent character distinguishing immature males as well as females. A faint reddish tinge can be seen just behind the marginal wing-coverts. -- S.J. Lang/VIREO
Figure 4. Immature female Rose-breasted Grosbeak, September 1987, Storrs, Connecticut showing dull "saffron-yellow" wing linings and the rich tawny-buff colorations on the underparts. Heavy breast streaks are evident. -- Louis R. Bevier
Figure 5. Female Black-headed Grosbeak, May 1982, Madera Canyon, Arizona. The white supercilium and median crown-stripes might are more typical of Rose-breasted, but occur on Black-headed as well. Despite the obvious flank streaks, the streaks are finest in the middle of the breast. The warm buff coloration on this bird can be matched by some Rose-breasted Grosbeaks, particularly immature males. The dark upper mandible is typical of Black-headed Grosbeaks. -- B. Randall/VIREO
Figure 6. Typical immature female Black-headed Grosbeak, May 1973, Silver City, New Mexico. The uniform tawny underparts are virtually unstreaked. Note the buffy supercilium and dark bill. -- D. & M. Zimmerman/VIREO
Figure 7. Immature male Black-headed Grosbeak. The blackish crown stripes, and upperparts indicate that this is a male and not a female as incorrectly listed in the VIREO catalog. Note also the prominent white spot at the base of the primaries. The worn remiges suggest that this individual is in its first summer. Note that most wing-coverts and tertials have been replaced and are adult type. -- H. Clarke/VIREO