After reading Dale A. Zimmerman’s (1955) paper on shrike identification, I began to investigate whether Northern Shrikes could be sexed and age-classified (in some cases) in the field. I wasn’t sure at what confidence level sex/age classifications could be attributed while in the field but considered that in some cases, birders reviewing their photographs from the field could analyze their shrike subject further and possibly assign to ‘category’ level. I soon encountered another paper on the subject, this time by Brady et al. (2009), and my interest in the subject piqued even more so.
Figure 1: A probable adult male Northern Shrike (Lanius excubitor) showcasing an uninterrupted jet black mask (loral region lacking grayish spur or grayish flecking throughout) (Zimmerman 1955); light gray upperparts devoid of any brownish flecking; unmarked, whitish throat; light, crisp barring below (Brady et al. 2009). Photo: Katherine Scott Jarvis. Algonquin Highlands, Haliburton County, Ontario. 4 February 2016.
Figure 2: A probable adult male Northern Shrike (Lanius excubitor). This example again showcases the uninterrupted jet black mask (loral region lacking grayish spur or grayish flecking throughout); light gray upperparts devoid of any brownish flecking; unmarked, whitish throat typical of adult males. The under-barring on this individual has been almost entirely obliterated by wear/fading, as can occur in late winter/early spring individuals (Pittaway 1999). Photo: Charmaine Anderson. Whitby, Durham Region, Ontario. 10 February 2016.
What I believe to be true at this point in my thinking:
- Adult males can be classified in the field with a high degree of certainty (given good, close looks in the field) or analysis of high-quality photos afterwards. Classic adult males showcase an uninterrupted jet black mask (loral region lacking grayish spur or grayish flecking throughout) (Zimmerman 1955); light, silvery-gray upperparts devoid of brownish flecking; unmarked, whitish throat; and average fainter and crisper barring below. Perhaps only adult males can be safely sexed in the field?
- Compared to adult males, adult females average more coarsely barred and brownish below; light brownish barring to the throat; brownish flecking throughout the upperparts and a more significant interruption to the loral region of the black mask (Zimmerman 1955).
- First winter birds are brownish throughout and similar in appearance with both males and females showcasing a lack (or complete absence of) black/deep brown to the loral region, with the mask being restricted to a post-ocular wedge. Black tones are said to be restricted to males with brownish tones restricted to females (Zimmerman 1955). Here’s a link to a photo of a bird that I believe is likely a first-winter female. Note on this first winter bird that the post-ocular wedge is brownish (vs blackish in males) in tone: https://www.flickr.com/photos/56326961@N03/5236605424/in/photolist-8YJYmq-ruNaJh-rPs186-rMgudf-hK5rka-DbeKab-8PKsNY-7TaMto-6d7hoX-e6ehnS-4yBM5H-C6SSXN-3MMsJ2-4nvpuc-phkdnG-7cppJw-63dkCW-oHzMDb-AdP8cP-zfXAur-aU3vfk-qLK6AW-joYvvb-oqpCHJ-94UTjc-BHD5sM-9mEPmf-njRqrU-9cSwQE-qBKtDZ-qBDkyd-nqiq6D-wJdSFd-9jRRGb-kKBTDL-qKyomp-9jLD7u-dWgk3T-9jHyQH-9o7FL4-9jLDWJ-dP6Ef7-bJ4vke-4BK8wx-9aNg2N-bwfLEj-iKyrbD-j8BJ5w-dvCAL4-gucx1F.
- Immatures can be quite adult-like in appearance. See Ryan Brady’s blog post for more information, including excellent photographs and commentary: http://northwoodsbirding.blogspot.ca/2008/01/ageing-northern-shrikes-in-field_10.html
- Late winter adults are less barred throughout with some birds (esp males, which average lighter barring to the underside) may be near completely unmarked by March, and this must be considered when analyzing birds in the field or photos (Pittaway 1999).
Comments on the content or thoughts from your field observations are welcomed!
Sincere thanks to Katherine Scott Jarvis and Charmaine Anderson for kindly availing the use of their excellent captures of Northern Shrikes. Ryan Brady shared his thoughts and also provided a link to a blog post of his from 2008 which details techniques on ageing shrikes in the field. Thanks also to Marcel Gahbauer for giving helpful feedback on some vague and potentially misleading terms used in the first installment of this post.
Brady, R.S., J.D. Paruk, and A.J. Kern. 2009. Sexing adult Northern Shrikes using DNA, morphometrics, and plumage. Journal of Field Ornithology 80:198–205.
Pittaway, R and M. King. 1999. Loggerhead and Northern Shrike ID. OFO News 17(1): 6-7.
1955. Notes on shrike identification and comparative behaviour of shrikes in winter. Wilson Bulletin 67(3): 200-208.