Identification of juvenile Lincoln’s Sparrow
Head: 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 is poorly-defined, and blends into the lateral crown stripes; the lateral crown stripes are greyish and finely marked with dark brown/blackish streaking. The edge to the upper portion of the supercilium averages more weakly defined than on Swamp Sparrow. 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. Lincoln’s appear more muted in colour, overall. They have less sharply-defined edges throughout the head; have less blackish (more brownish) detailing throughout, and average slightly duller chestnut edging throughout the flight feathers.
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 perceptibly more delicate in build compared to Swamp. The bill averages slightly lighter in build, being more slender and narrow, and sometimes appears shorter; when viewing the ‘face’ in its entirety, this sets off a “cuter” expression.
Greater coverts: Next in rung, in terms of field-applicability, is a look at the greater coverts. In Lincoln’s, each greater covert feather is dark, mainly blackish, with buff edging. This contrast averages slightly duller than the black-centred, bright buff edging seen with Swamp Sparrows. Note that this detail could 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 streaking to the underside of Lincoln’s average slightly more extensive, marginally crisper, somewhat lighter in colour (lighter brown) than Swamp? I believe so, but these are averages, not absolutes.
Legs and feet: After reviewing hundreds of photos of both species, I couldn’t help but notice that the tarsi and feet of Lincoln’s Sparrows are daintier in build compared to Swamp. I’m not sure if this is described in the literature? Perhaps it’s an old hat field impression.
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, 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, 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 challenging and requires a multi-character analysis of plumage detail. Hopefully, this ID guide proves to be helpful to those looking to separate the two species!
Acknowledgements
Thank you to Wayne Renaud and Frank King for the use of their photos of juvenile Swamp Sparrows.
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.