One of the most fascinating things about my favorite birds — the nightingale-thrushes (genus Catharus) — is how they change color. The birds molt once per year, in the late summer after breeding has concluded. Over the next few months, the rich colors of the fresh fall plumage start to fade, and by the following spring they have changed so much that differences among subspecies are masked by individual variation. The best (and sometimes only) way to see the geographic variation in color among the various subspecies is to examine specimens collected in fresh fall plumage — or, to catch different subspecies in the Darién Gap of Colombia during their fall migrations.
Modern field guides do not depict the changes that occur within each individual throughout the year. Nor, to my knowledge, has any field guide attempted to depict the geographic variation in color that occurs in the five species that breed in North America. Our only means of studying this variation is in the museum, where specimens from distant localities can be compared under a single light source.
On a recent trip to the American Museum of Natural History (AMNH) in New York, I assembled a series of specimens in fresh fall plumage to illustrate, via digital photograph, some of the subspecific variation in coloration that occurs within and between Hermit Thrush (C. guttatus) and Swainson’s Thrush (C. ustulatus) in eastern and western North America. (Many thanks to Paul Sweet, Bentley Bird and Thomas Trombone for their assistance in the AMNH collection).
I doubt that many people have seen such an image before. Note how closely the plumage of the eastern Hermit Thrush (C. g. faxoni) matches that of (one of the) western (coastal) forms of Swainson’s Thrush (C. u. oedicus). Also, there is considerable color variation between two specimens of C. g. osgoodi collected at the same locality, on Middleton Island in southern Alaska. You may also note the similarity in dorsal coloration of the darker individual of C. g. osgoodi to eastern Swainson’s Thrush (C. u. swainsoni).
For more information about nightingale-thrushes, check out some of my papers about their evolutionary history, behavior and taxonomy:
- Halley, M. R. 2018. The ambiguous identity of Turdus mustelinus Wilson, and a neotype designation for the Veery Catharus fuscescens (Stephens). Bulletin of the British Ornithologists’ Club 138(2): 78–91. DOWNLOAD PDF
- Halley, M. R., Klicka, J., Sesink Clee, P., and J. D. Weckstein. 2017. Restoring the species status of Catharus maculatus (Aves: Turdidae), a secretive Andean thrush, with a critique of the yardstick approach to species delimitation. Zootaxa 4276(3): 387–404. DOWNLOAD PDF
- Halley, M. R., Heckscher, C. M., and V. Kalavacharla. 2016. Multi-generational kinship, multiple mating, and flexible modes of parental care in a breeding population of the Veery (Catharus fuscescens), a trans-hemispheric migratory songbird. PLoS ONE 11(6): e0157051. doi:10.1371/journal.pone.0157051
- Heckscher, C. M., Halley, M. R., and P. Stampul. 2015. Intratropical migration of a Nearctic-Neotropical migratory songbird (Catharus fuscescens) in South America with implications for migration theory. Journal of Tropical Ecology 31: 285–289. DOWNLOAD PDF
- Halley, M. R. 2014. Slaty-backed Nightingale-Thrush (Catharus fuscater), Neotropical Birds Online (T. S. Schulenberg, Editor). Ithaca: Cornell Lab of Ornithology. READ ONLINE
- Halley, M. R. 2014. Kin structure and mating system of the Veery (Catharus fuscescens) in the Mid-Atlantic Piedmont. MS Thesis, Delaware State University READ ONLINE
- Halley, M. R., and C. M. Heckscher. 2013. Interspecific parental care by a Wood Thrush (Hylocichla mustelina) at a nest of the Veery (Catharus fuscescens). Wilson Journal of Ornithology125(4): 823–828. DOWNLOAD PDF
- Halley, M. R., and C. M. Heckscher. 2012. Multiple male feeders at nests of the Veery. Wilson Journal of Ornithology 124(2): 396–399. DOWNLOAD PDF