Plumages, Molts, and Structure

Blue-throated Barbet has 10 primaries (numbered distally, from innermost p1 to outermost p10, and with the p10 reduced in size), 12 secondaries (numbered s1-s8 proximally and including 4 tertials, numbered t1 to t4 distally), and 10 rectrices (numbered distally, r1 to r5, on each side of the tail). Geographic variation is moderate (see Systematics); the following pertains to the nominate subspecies and is based on descriptions in Short and Horne (1 Short, L. L., and J. F. M. Horne (2001). Toucans, Barbets and Honeyguides. Oxford University Press, Oxford, UK. Close , 2 Short, L. L., Jr. and J. F. M. Horne (2002). Family Capitonidae (Barbets). In Handbook of the birds of the World, Volume 7: Jacamars to woodpeckers (J. del Hoyo, A. Elliott and J. Sargatal, Editors), Lynx Ediciones, Barcelona, Spain. pp 140-219. Close ) along with examination of images in Macaulay Library. See Molts for molt and plumage terminology. Sexes are similar in all plumages. Definitive appearance is assumed following the Second Prebasic Molt.

Natal Down

No information.

Juvenile (First Basic) Plumage

Juvenile Plumage is similar to that of later plumages but colors are often muted and dull. The blue of the head can be reduced and sometimes replaced by dusky. The red of the forecrown can be dull or tinged orange. The dark forecrown bar is blue and black, the black being more sooty. The blue on the head is duller, as is the green of the body, and red on the underparts is absent. In some individuals these colors on juvenile feathers may be brighter. Juvenile flight feathers are narrower and edged with duller green than basic feathers, the outer primaries and rectrices being browner (with wear) and more rounded at the tips (less truncated) than basic feathers. Juvenile underpart feathers are more filamentous than in later plumages due to lower barb densities. The Preformative Molt may commence shortly after or even sometimes before fledging, as suspected in other Asian barbets; study is needed.

Formative Plumage

Formative Plumage is similar to Definitive Basic Plumage but is separable by the retention of the juvenile flight feathers and molt limits between formative and juvenile upperwing coverts and sometimes tertials, as has been found in other barbets (see Molts). Body plumage appears to be similar to that of definitive basic plumage but averaging duller green, with the blue, red, and black feathering of the head and breast averaging duller and the red spots of the underparts reduced or absent. Retained juvenile flight feathers are relatively narrow, browner and with duller edging, and worn, the rectrices and outer primaries tapered or rounded rather than truncated at the tips. See also Bare Parts for iris color changes that can be helpful in ageing.

Definitive Basic Plumage

Black rictal bristles project forward from the base of the bill. Forehead deep red with black feather bases forming a black line along the base of the bill towards the lore, and feathers above with dull yellow tips forming band across forecrown. A black band extends to either side of the crown, above the eye, which extends toward the nape on each side of the crown. This black band encloses a red patch that forms the rest of the hindcrown and the nape. A bright blue line is present above the eye and this blue encompasses most of the sides of the head, extending to the lores, chin, throat, and upper breast, with a small, red-and-black spot on the malar (sometimes missing entirely) and two red spots on either side of the blue on the throat; the rear portion of the auriculars and sides of the neck are green. Upperparts and upperwing coverts are generally dark green, sometimes with yellow-green edges to the body feathers and often with a blue wash to the primary coverts. Uppertail coverts green with dark feather shafts. Remiges and rectrices are dusky to blackish with bright green to yellow-green outer webs. The underparts below the blue breast are a paler yellower green that the upperparts; the undertail coverts can be cast bluish green. The underwing coverts are pale yellow-white at the base, grading to blue-green at the bend of the wing, and black distally.

Definitive Basic Plumage is separated from Formative Plumage by brighter average body feathering with the red, blue, and black feathering of the head and upper breast averaging brighter. Basic flight feathers are relatively broad and darker slate to blackish with bight glossy green edging, relatively fresh, and with the rectrices and outer primaries truncated at the tips. See also Bare Parts for iris color changes that can be helpful in ageing.

Aberrant Plumages

Some individuals of the nominate subspecies (notably in northwestern India) can exhibit striking erythrism, with body plumage other than the head and sometimes some upperwing coverts red or (undeprarts) red mottled yellow; these were at one time considered a separate subspecies (see Systematics).

Molt and plumage terminology follows Humphrey and Parkes (3 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. (4 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, the latter generally referred to as “life-cycle” molt terminology (5 Jenni, L., and R. Winkler (2020). Moult and Ageing of European Passerines. Second edition. Bloomsbury, London, UK. Close ; see also 6 Pyle, P. (2022). Defining moults in migratory birds: a sequence-based approach. Journal of Avian Biology 2022(5):e02958. Close ).

Molt strategies in Blue-throated Barbet are little studied (1 Short, L. L., and J. F. M. Horne (2001). Toucans, Barbets and Honeyguides. Oxford University Press, Oxford, UK. Close ) and complicated by likely year-round breeding in some but not all populations (see Breeding: Phenology). It appears to show a Complex Basic Molt Strategy with a partial preformative molt and complete (possibly occasionally incomplete) prebasic molts but no prealternate molts. The information below is based that in Short and Horne (1 Short, L. L., and J. F. M. Horne (2001). Toucans, Barbets and Honeyguides. Oxford University Press, Oxford, UK. Close , 2 Short, L. L., Jr. and J. F. M. Horne (2002). Family Capitonidae (Barbets). In Handbook of the birds of the World, Volume 7: Jacamars to woodpeckers (J. del Hoyo, A. Elliott and J. Sargatal, Editors), Lynx Ediciones, Barcelona, Spain. pp 140-219. Close ), and Johnson and Wolfe (7 Johnson, E. I., and J. D. Wolfe (2017). Molt in Neotropical Birds: Life History and Aging Criteria. Studies in Avian Biology 51. CRC Press, Boca Raton, Florida, USA. Close ) for New World barbets, along with examination of images in the Macaulay Library; details still need to be worked out.

Prejuvenile Molt

Prejuvenile molt occurs in the nest. There is no information on timing of development.

Preformative Molt

The Preformative Molt appears to be partial as described for new world barbets (7 Johnson, E. I., and J. D. Wolfe (2017). Molt in Neotropical Birds: Life History and Aging Criteria. Studies in Avian Biology 51. CRC Press, Boca Raton, Florida, USA. Close ), including most to all body feathering and upperwing lesser and median coverts, some proximal greater coverts, and sometimes 1-3 tertials, but no primary coverts, primaries, secondaries besides tertials. In other barbets some central to all rectrices may be replaced in some individuals. See images under Formative Plumage). Preformative molt probably begins early, shortly after fledging or perhaps commencing prior to fledging as can occur in other barbets and woodpeckers.

Definitive Prebasic Molt

The Definitive Prebasic Molt likely occurs within 1-5 months following breeding, which may be year-round. This molt appears typically to be complete but may occasionally often be arrested (incomplete) before all flight feathers are replaced, or may be suspended for breeding in some cases. As in most or all barbets, primaries molt distally from innermost p1 to outermost p10 and secondaries may have two molt centers: one from the inner tertial (t1) distally or 2nd or 3rd tertial (t2 or t3) bidirectionally, and another one from the outermost s1 proximally. Evidence for possible commencement at t3 instead of t2 in some barbets is of interest and may indicate that the extra tertial (compared with other birds that have three tertials and begin molt at t2) may have evolved among t1–t2. Barbets may also be diastataxic, whereby secondaries molt proximally from s1 and s5 as well as distally from the tertials; study is needed. Rectrices in barbets show various sequences (1 Short, L. L., and J. F. M. Horne (2001). Toucans, Barbets and Honeyguides. Oxford University Press, Oxford, UK. Close ) but a common pattern may be bidirectional replacement on each side of the tail from r2 or r3 (1 Short, L. L., and J. F. M. Horne (2001). Toucans, Barbets and Honeyguides. Oxford University Press, Oxford, UK. Close , 7 Johnson, E. I., and J. D. Wolfe (2017). Molt in Neotropical Birds: Life History and Aging Criteria. Studies in Avian Biology 51. CRC Press, Boca Raton, Florida, USA. Close ). Variation in rectrix replacement sequence may be expected and replacement may occur out of synch with that of primaries and secondaries.

Bill and Gape

The bill is short and curved with the lateral base of the maxilla expanded. Coloration is bicolored, black or blue-black along the ridge of the upper mandible to the tip, with a greenish-gray to yellowish base of the maxilla and about half of the lower mandible (1 Short, L. L., and J. F. M. Horne (2001). Toucans, Barbets and Honeyguides. Oxford University Press, Oxford, UK. Close ). The colors can be duller and the blackish less distinctly defined in juvenile and first-year birds.

Iris and Facial Skin

The eye in adults is reddish-brown to orangish and the orbital skin is brown, green-brown, or yellowish grading into orange-brown eyelids. In juveniles and first year birds the iris is duller and grayer than adults and the orbital skin can be dull and dusky (1 Short, L. L., and J. F. M. Horne (2001). Toucans, Barbets and Honeyguides. Oxford University Press, Oxford, UK. Close ).

Tarsi and Toes

Tarsi and toes are slate gray to gray-green with paler soles and slaty-black claws (1 Short, L. L., and J. F. M. Horne (2001). Toucans, Barbets and Honeyguides. Oxford University Press, Oxford, UK. Close ).

Linear Measurements

Linear measurements are given in Table 1.

Mass

Masses are given in Table 1.

The olfactory bulb of this species is small, only 15.4% of the diameter of the corresponding cerebral hemispheres, compared to over 30% for procellariform seabirds that have a well-developed olfactory system (8 Bang, B. G., and S. Cobb (1968). The size of the olfactory bulb in 108 species of birds. Auk 85(1):55-61. Close ).