Plumages, Molts, and Structure

Rufous-brown Solitaire has 10 primaries (numbered distally, from innermost p1 to outermost p10, the p10 reduced in length), 9 secondaries (numbered proximally, from outermost s1 to innermost s9 and including 3 tertials, s7‒s9 in passerines), and 12 rectrices (numbered distally, from innermost r1 to outermost r6 on each side of the tail). Geographic variation is moderate among populations with disjunct ranges (see Subspecies); the following plumage descriptions cover all subspecies and are based on those of Ridgely and Tudor (2 Ridgely, R. S., and G. Tudor (1994). The Birds of South America. Volume 2: The Suboscine Passerines. University of Texas Press, Austin, TX, USA. Close ) and Collar (3 Collar, N. J. (2005). Family Turdidae (thrushes). In Handbook of the birds of the World, Volume 10: Cuckoo-shrikes to thrushes (del Hoyo, J., A. Elliott and D. A. Christie, Editors), Lynx Edicions, Barcelona, Spain. pp. 514–810. Close ), along with examination of Macaulay Library images; see Pyle (4 Pyle, P. (2022). Identification Guide to North American Birds. Part I, Second Edition. Slate Creek Press, Forest Knolls, CA, USA. Close ) for age determination criteria among similar species of solitaires and thrushes. See Molts for molt and plumage terminology. Sexes appear similar in all plumages. Definitive appearance is attained following the Second Prebasic Molt. Timing of breeding and thus plumage development unknown but plumages may be expected to occur throughout the year among all populations; study is needed.

Natal Down

Natal Down is present in the nest and is undescribed for Rufous-brown Solitaire. In other solitaires (e.g. Townsend's Solitaire (Myadestes townsendi)), natal down is blackish neutral gray, sparsely distributed on capital and dorsal pterylae.

Juvenile (First Basic) Plumage

Likely present 1–3 months following fledging. As in other thrushes and solitaires, Juvenile Plumage appears to be like later plumages but is duller overall and has diffuse buff spots to the upperpart and breast feathers and diffuse buff marks or tips to the inner and often outer upperwing secondary coverts. Spots on juvenile body feathers appear to be rather indistinct as compared with those of some other solitaires and thrushes. Juvenile body feathering, especially undertail coverts, is more filamentous due to lower barb densities, and juvenile remiges and rectrices are relatively narrow and more tapered or pointed at the tips.

Formative Plumage

Likely present 3–10 months following fledging, becoming increasingly worn over this period. Similar to Definitive Basic Plumage but may average duller and can be distinguished by molt limits among the upperwing coverts along with condition of retained juvenile flight feathers. Most to all lesser coverts, some to all inner median coverts, and no to a few inner greater coverts appear to be replaced during Preformative Molts, the formative coverts are fresher, darker rufous or brownish rufous, and of better quality, contrasting with weaker and more faded pale rufous-orange juvenile outer coverts, some to many of which can show diffuse buff markings or tips if not worn off. Flight feathers are retained, the juvenile outer primaries are relatively narrow, tapered at the tips, and becoming increasingly abraded with wear. Retained juvenile rectrices are narrow, tapered or pointed at the tips, and relatively worn compared to basic rectrices at the same stage of the molt cycle.

Definitive Basic Plumage

Likely present from 2–11 months following breeding, becoming increasingly worn over this period. Head, upperparts, throat, and upper breast are rufous-brown, dark cinnamon, or brownish rufous, the head and throat are often slightly more saturated in color. Pale whitish to yellow orbital skin forms a variably distinct eye ring on the plain face. Rectrices, remiges, and upperwing coverts are dusky with rufous-brown to brownish rufous outer webs, rather uniform in color with the upperparts. Underparts are dingy whitish, the central breast (below the rufous bib) washed gray, the lower flanks and ventral feathers washed tawny, and the undertail coverts bright cinnamon. Underwing coverts dingy whitish.

Definitive Basic Plumage is best separated from Formative Plumage by averaging brighter rufous overall; upperwing coverts are uniform in wear, without molt limits, and without diffuse buff spots or tips; outer primaries and rectrices are broader, duskier, relatively fresher, and more truncate at the tips than juvenile feathers.

Molt and plumage terminology follows Humphrey and Parkes (5 Humphrey, P. S., and K. C. Parkes (1959). An approach to the study of molts and plumages. Auk 76(1):1–31. Close ) as modified by Howell et al. (6 Howell, S. N. G., C. Corben, P. Pyle, and D. I. Rogers (2003). The first basic problem: a review of molt and plumage homologies. Condor 105:635–653. Close ). Under this nomenclature, terminology is based on evolution of molts along ancestral lineages of birds from ecdysis (molts) of reptiles, rather than on molts relative to breeding season, location, or time of the year (see 4 Pyle, P. (2022). Identification Guide to North American Birds. Part I, Second Edition. Slate Creek Press, Forest Knolls, CA, USA. Close , 7 Pyle, P. (2022). Defining moults in migratory birds: a sequence-based approach. Journal of Avian Biology 2022(5):e02958. Close for more information). Rufous-brown Solitaire shows a Complex Basic Molt Strategy, as in all other solitaires and thrush species (4 Pyle, P. (2022). Identification Guide to North American Birds. Part I, Second Edition. Slate Creek Press, Forest Knolls, CA, USA. Close ), with a partial preformative molt and complete prebasic molts but no prealternate molts. Timing of breeding and thus of molts are poorly known and likely variable among populations (see Breeding: Phenology) but the occurrence of each molt might be expected throughout the year among all populations; study is needed.

Prejuvenile (First Prebasic) Molt

The Prejuvenile Molt occurs in the nest. There is little information on this molt in Rufous-brown Solitaire.

Preformative Molt

Partial, including most or all body feathers, some to all upperwing lesser coverts, no to most or all median coverts, and no to a few inner greater coverts, but no primary coverts, primaries, secondaries, or rectrices (based on examination of Macaulay Library images). This extent is typical of Turdidae, although appearing to average less extensive than migratory North American species (cf. 4 Pyle, P. (2022). Identification Guide to North American Birds. Part I, Second Edition. Slate Creek Press, Forest Knolls, CA, USA. Close ). See images under Formative Plumage.

Definitive Prebasic Molt

Few to no images of birds undergoing this molt are present in the Macaulay Library, suggesting that birds are furtive and hiding during this process. As in most passerines and all Turdids, primaries are undoubtedly replaced distally (from innermost p1 to outermost p10), secondaries bilaterally from the second tertial (s8) and proximally from the innermost (s1), and rectrices from the central feather (r1) distally on each side of the tail, with some variation in sequence to be expected.

Descriptions below based primarily on examination of Macaulay Library images. Bill and leg color may become brighter during courting and pre-breeding periods and duller during molting periods; study is needed.

Bill and Gape

The bill is relatively stout, pointed, and slightly hooked at the tip. In adults, the maxilla is blackish and the mandible is bright yellow to orangish yellow. In juveniles it is dingy grayish with a yellow base, gradually becoming brighter yellow during the first year. The gape is bright yellow, swollen, and conspicuous in younger juveniles and still thinly evident in adults.

Iris and Facial Skin

The iris is dark reddish brown to reddish in adults. In juveniles it is duller and grayer brown, gradually becoming browner or dull reddish brown during the first year. The orbital skin in adults can be bright yellow to dull yellowish (perhaps brighter during prebreeding periods); in juveniles, the color is duller and grayer.

Tarsus and Toes

In adults, legs and feet are yellowish to brownish yellow and may become brighter during prebreeding periods. Legs and feet are darker and grayer in juveniles and become dull yellowish during the first year.

Linear Measurements

Overall length: 20–21 cm.

Beak length (total culmen): male, 18.57 mm ± 1.48 SD (n = 3); female, 18 mm ± 0.71 (n = 2) (8 Tobias, J. A., C. Sheard, A. L. Pigot, A. J. Devenish, J. Yang, F. Sayol, M. H. Neate‐Clegg, N. Alioravainen, T. L. Weeks, R. A. Barber, P. A. Walkden, et al. (2022). Avonet: Morphological, ecological and geographical data for all birds. Ecology Letters 25:581–597. Close ).

Beak width: male, 4.97 mm ± 0.61 SD (n = 3); female, 4.55 mm ± 0.07 (n = 2) (8 Tobias, J. A., C. Sheard, A. L. Pigot, A. J. Devenish, J. Yang, F. Sayol, M. H. Neate‐Clegg, N. Alioravainen, T. L. Weeks, R. A. Barber, P. A. Walkden, et al. (2022). Avonet: Morphological, ecological and geographical data for all birds. Ecology Letters 25:581–597. Close ).

Beak depth: male: 4.87 mm ± 0.23 SD (n = 3); female: 5.45 mm ± 0.07 (n = 2) (8 Tobias, J. A., C. Sheard, A. L. Pigot, A. J. Devenish, J. Yang, F. Sayol, M. H. Neate‐Clegg, N. Alioravainen, T. L. Weeks, R. A. Barber, P. A. Walkden, et al. (2022). Avonet: Morphological, ecological and geographical data for all birds. Ecology Letters 25:581–597. Close ).

Tarsus length: male, 22.6 mm ± 0.72 SD (n = 3); female, 22.9 mm ± 0.42 (n = 2) (8 Tobias, J. A., C. Sheard, A. L. Pigot, A. J. Devenish, J. Yang, F. Sayol, M. H. Neate‐Clegg, N. Alioravainen, T. L. Weeks, R. A. Barber, P. A. Walkden, et al. (2022). Avonet: Morphological, ecological and geographical data for all birds. Ecology Letters 25:581–597. Close ).

Wing length: male, 106 mm ± 1.73 SD (n = 3); female, 104.5 mm ± 3.54 (n = 2) (8 Tobias, J. A., C. Sheard, A. L. Pigot, A. J. Devenish, J. Yang, F. Sayol, M. H. Neate‐Clegg, N. Alioravainen, T. L. Weeks, R. A. Barber, P. A. Walkden, et al. (2022). Avonet: Morphological, ecological and geographical data for all birds. Ecology Letters 25:581–597. Close ).

Mass

61 g (9 Dunning, J. B., Jr. (2008). CRC Handbook of Avian Body Masses. Second edition. CRC Press, Boca Raton, FL, USA. Close ).