Separating juvenile Lincoln’s from Swamp in the Field

Several summer’s ago, I made a brief attempt to approach the study of juvenile Lincoln’s vs. Swamp sparrows, and noticed that all apparent avenues to field ID success were blocked by the lore. I sputtered in interest the following summer, and again wound up turned off/disinterested. Just yesterday, however, I posted a photo of a juvenile Melospiza on my Facebook page, and a birder inquired “not LISP (Lincoln’s Sparrow) ?” My curiosity peaked, and I decided the following day (today, 24 July 2017) I would sit down and study the two. I poured myself some coffee, prepped a study soundtrack, and gathered all pertinent materials (Rimmer 1986, Pyle 2001,  Sibley 2014). I opened up Flickr, and opened up both species’ photo pages in Migration Research Foundation, and the Macaulay Library. I set aside a notepad, two of my favourite pens, and was ready to give this identification dilemma another effort.

A comment on juvenile plumage

For eastern and southern Ontario birders, juvenile Lincoln’s Sparrows are not often (or should I say, are rarely) encountered. This briefly-held plumage (July-August) occurs on this species’ natal grounds. Before Lincoln’s migrate south from their boggy, shrub wetland habitat throughout the boreal, they molt into first basic (first year; HY) plumage, which is more-or-less adult-like, and less likely to cause confusion among birders. Swamp Sparrows are widespread throughout eastern and southern Ontario, and for birders spending time in the field during the summer months (July-August), they become acquainted with the juvenile plumage of this species.

Eastern Ontario bogs — the wellspring of the dispersed?

Curiously, the juvenile Lincoln’s Sparrow that was found at the Embrun Sewage Lagoons on 23 July 2017 was found within reasonable distance to known breeding sites for this species. Take for example the following list of sites, followed by the distance (as the wee Lincoln’s flies) from: Larose Forest (probable sites within; 8-10 km), Morewood Bog (likely sites within; 12 km), Mer Bleue (known site; 25 km), and Alfred Bog (known site; 36 km). Therefore how does the above information affect the role of probability in making quick assessments of juvenile LISP/SWSP in the field whenever one birds within the vicinity of eastern ON “bog country?” Is it a safe assumption to immediately label a mid-summer juvenile as a Swamp Sparrow, as I did on 23 July 2017, based on probability? Yesterday, the answer was yes, today the answer is no. The new answer is: if photos are obtained, the bird can be identified by reviewing a suite of features, then combining the multiple parts of the analysis to form the whole picture of the bird. Can juveniles of the two be differentiated in the field, given short views through binoculars, sans review of photos afterward? Hard to say. For me, right now, I will lean on post-outing analysis to develop my Melospiza legs before brazen attempts at quick field identifications. For me, the gateway to learning more about this particular ID issue has only just re-opened…so, lot’s to learn!

Identification of juvenile Lincoln’s Sparrow

In order to prepare myself for analysis, I read Rimmer 1986, and read the species’ accounts in Pyle 1997, Rising & Beadle 2002, and browsed Sibley 2014. I spent several hours reviewing photos of both species online, via Macaulay Library. I visited Flickr, but there were many mis-ID’s, so I closed the page to avoid confusing myself! After this morning’s study, I see that the identification of juvenile Lincoln’s Sparrows is possible in the field, but requires correct interpretation of multiple characters. These characters, from greatest weight to least weight, are as follows:

Head: For the purposes of field ID, the greatest potential analytical weight stems from this region. On Lincoln’s, the crown detail is especially important. The crown is wholly brown to buffy-brown with distinct black streaking throughout. The median crown stripe being poorly-defined, blending, and showing low contrast with, the lateral crown stripes ; the lateral crown stripes are grayish-brown and finely peppered with dark brown/blackish streaking. The edge to the upper portion of the supercilium averages more weakly defined than on Swamp Sparrow (personal observation). The moustachial and malar stripes appear, on average, less distinct, and slightly narrower compared to Swamp. The throat is often lightly streaked, especially along its edges. In its entirety, the head detail of a Lincoln’s Sparrow is quite muted overall compared to that of Swamp. There are less blackish tones throughout, and less sharply defined edges.

The bird in its entirety: In my opinion, second-rung behind head detail. Take in the entire bird, as a single package. Lincoln’s appear more muted in colour, overall. They appear not as dark as Swamp Sparrows. They have less sharply-defined edges throughout the head; have less blackish (more brownish) detailing throughout; and average slightly duller chestnut edging throughout the remiges.

Bill: Regardless of morphometric measurements, the importance for here is field applicability: is the difference perceptible. Photo after photo, the bill of a Lincoln’s is, by in large, perceptibly more delicate in build compared to Swamp. The bill averages slightly lighter in build, being more slender and narrow, and sometimes appears shorter. This sets off a “cuter” expression when the “face” is viewed as a whole.

Greater coverts: Next in rung, in terms of field-applicability, is a look at the greater coverts. In Lincoln’s, the each greater covert feather is dark, essentially blackish, with buff edging. This contrast averages slightly duller than the black-centered, bright buff edging seen with Swamp Sparrows. Note that this detail would be extremely difficult to correctly interpret without the use of photos of the specimen to examine once back home from the field.

Underpart streaking: Lincoln’s average more heavily-streaked throughout the underside, especially along the sides of the breast and just below the edges of the chin, where dense streaks rain down upon a buffy bloom to the entire chest. There is a surprising degree of overlap in this feature, however, so it’s not at all bulletproof. Does the underside streaking on a Lincoln’s average slightly more extensive, slightly crisper, slightly lighter in colour (lighter brown) than Swamp? I believe so, but these are averages, not absolutes.

Legs and feet: As far as I know, this is not described, and may not even be a real thing, but. After reviewing hundreds of photos of both species, I noticed that the tarsi and feet of Lincoln’s Sparrows are daintier in build compared to Swamp. The tarsi appear thinner, and each of the toes is also thinner.

Buffy “bib”: This is a shared characteristic of juveniles of both species. My assumption is Lincoln’s are more likely to show consistency in this feature; Swamp possibly less likely. I wouldn’t give it much weight. It’s easy to see the classic adult Lincoln’s-buff in a juvenile bird, but know that it’s a shared character between the two species.

Photographs

Figure 1: Crown detail. Juvenile Lincoln’s Sparrow, Embrun Sewage Lagoons, Embrun, Ontario. 23 July 2017.

Figure 2: Crown detail. Juvenile Lincoln’s Sparrow, Embrun Sewage Lagoons, Embrun, Ontario. 23 July 2017.

 

Figure 3: Overall bird detail, juvenile Lincoln’s at left; juvenile Swamp at right. At left photographed at the Embrun Sewage Lagoons, Embrun, Ontario on 23 July 2017. At right photographed at the Nonquon Sewage Lagoons in Port Perry, Ontario on 21 July 2017. Copyright Wayne Renaud. Note also in this photo the delicate build of the legs and feet of the Lincoln’s in direct comparison to the Swamp (relative size difference between birds in photos was manipulated by eyeballing, so therefore it is not exact)

Figure 4: Overall bird detail, juvenile Lincoln’s at left; juvenile Swamp at right. At left photographed at the Embrun Sewage Lagoons, Embrun, Ontario on 23 July 2017. At right photographed in St. John’s, Newfoundland, on 22 July 2017. Copyright Frank King. Note also in this photo the delicate build of the legs and feet of the Lincoln’s in direct comparison to the Swamp (relative size difference between birds in photos was manipulated by eyeballing, so therefore it is not exact)

Figure 5: Overall bird detail, juvenile Lincoln’s at left; juvenile Swamp at right. At left photographed at the Embrun Sewage Lagoons, Embrun, Ontario on 23 July 2017. At right photographed in St. John’s, Newfoundland, on 22 July 2017. Copyright Frank King. Note also in this photo the delicate build of the legs and feet of the Lincoln’s in direct comparison to the Swamp (relative size difference between birds in photos was manipulated by eyeballing, so therefore it is not exact)

Figure 6: Bill detail. Juvenile Lincoln’s Sparrow, Embrun Sewage Lagoons, Embrun, Ontario. 23 July 2017.

Figure 7: Bill detail. Juvenile Lincoln’s Sparrow, Embrun Sewage Lagoons, Embrun, Ontario. 23 July 2017.

Figure 8: Greater covert detail. Juvenile Lincoln’s Sparrow, Embrun Sewage Lagoons, Embrun, Ontario. 23 July 2017.

 

Closing comments

Separating juvenile Lincoln’s from Swamp is extremely difficult, and requires a multi-character analysis of plumage detail. Obtaining photos and reviewing them on a high quality, colour-corrected monitor is highly recommended. Revealing un-subtantiated field ID to others, such as walking up to a group of eastern Ontario birders and stating “I saw a juv Lincoln’s today” (takes sip of water, walks away) just doesn’t feel right … at least not yet (if ever?) The next step in this undertaking (learning more about separating the two) is posting this segment to the Facebook group, Advanced Bird ID, to see if it receives a passing grade. In fact, perhaps I’ll post this to ID Frontiers to really give myself the impression of slowly waving my hand back and forth above a heated element. Next up after that: perhaps a visit to the Canadian Museum of Nature. I must dodge the savvy birding brain of Michel Gosselin and pore over the collections completely independently, and without biases/impressions. Thank you very much for reading all 1300 words of this web article!

Acknowledgements

Thank you to Wayne Renaud for use of his photo of a juvenile Swamp Sparrow, thanks also to Greg Neise for posing the Q, “not Lincoln’s?” on my Facebook page and thank-you to the following members of the Advanced Birding in Ontario page for weighing in on the ID online: Victor Dillabaugh, Richard Beardon, Fred Urie, and Alison Jane Bentley. After these online comments, I was motivated to get to the bottom of this perplexing ID dilemma (if possible) 🙂

Recommended Reading/Reference List

Migration Research Foundation, McGill University: http://www.migrationresearch.org/mbo/id/lisp.html

Pyle, P. 1997. Identification guide to North American Birds. 2nd printing. Part I, Columbidae to Plocidae. Slate Creek Press, Bolinas CA.

Rimmer, C.C. 1986. Identification of juvenile Lincoln’s and Swamp Sparrows. Journal of Field Ornithology 57: 114-125. https://sora.unm.edu/sites/default/files/journals/jfo/v057n02/p0114-p0125.pdf.

Sibley, D.A. 2014. The Sibley Guide to Birds. 2nd ed. New York: Alfred A. Knopf.