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Peruvian Sheartail Thaumastura cora

  • Order: Caprimulgiformes
  • Family: Trochilidae
  • Monotypic
  • Authors: Clark, Christopher J.
Sections

Appearance

Distinguishing Characteristics

Peruvian Sheartail is a tiny hummingbird. Adult males are usually unmistakable, owing to the greatly elongated tail streamers with extensive white. These streamers often are broken or worn, however, and both streamers can be entirely missing. The remaining rectrices tipped in white.  The bill is short and straight; the body plumage has a solid green back, white or light gray belly, and an iridescent gorget that is pink in the center, and at most viewing angles, the hue shifts to cyan at the lateral edges.

Similar Species

Peruvian Sheartails is most similar in appearance to Chilean Woodstar (Eulidia yarrellii). The male sheartail, while usually unmistakable, can be difficult to distinguish from Chilean Woodstar if both streamers are broken; perched male Chilean Woodstar typically has a shorter tail with no white, and the tips of each side of the folded tail cross each other, whereas these tail tip does not cross in male Peruvian Sheartail.

Female Peruvian Sheartail is a challenge to distinguish from other small hummingbirds; it is pale on the ventral surface (throat, breast, belly, flanks), with the shade varying from off white to pale buff, it lacks the elongated tail or gorget of male, outer rectrices are ipped in white, and rectrix 2 (R2) is longest. Female Peruvian Sheartail are especially difficult to tell apart (in the field) from Chilean Woodstars where their ranges overlap in northern Chile. Chilean Woodstar female averages a whiter ventral surface (throat, breast and belly) than Peruvian Sheartail (Jaramillo 2003, van Dongen personal communication), but there is overlap and either species can be buff underneath (van Dongen personal communication, contra Jaramillo 2003). The proximal region of inner rectrices (R2-R3) is light buff in Chilean Woodstar and white in Peruvian Sheartail, but in the field this character will be difficult to assess because it is largely covered by tail coverts. Both species sometimes pump the tail repeatedly when foraging or hovering, in woodstar fashion; this is also not a good character to distinguish the species, contra Jaramillo (2003). In the field, the most reliable character appears to be the 'chip' call, which is produced frequently. Peruvian Sheartail produces a dry chip call that is lower pitched than that of the Chilean Woodstar. Female Chilean Woodstar also has a more rounded tail (R2 is only about 2 mm longer than R1) than Peruvian Sheartail, in which R2 is ca 6 mm longer than R1. In the hand, identification is easy: measurements of folded wing length, bill length, and tail shape are all diagnostic characters (see Measurements), in addition to the subtle color characters cited above.

Peruvian Sheartail is also similar in size to Short-tailed Woodstar (Myrmia micrura); besides differences in tail morphology, the male Short-tailed Woodstar’s gorget has a white malar stripe above it, lacking in Peruvian Sheartail. Female Short-tailed Woodstar is a similar shade of buff underneath but rectrices are diagnostic: and are shorter, more rounded, and with smaller white tips on the distal rectrices and entirely dark proximal rectrices. There is also little to no overlap in geographic ranges. Some overlap does occur with Purple-collared Woodstar (Myrtis fanny), but Peruvian Sheartail is smaller bodied, with a shorter, straighter bill. The back is a lighter shade of green than in Little Woodstar (Chaetocercus bombus).

Detailed Description

Adult male: Above: dull metallic (nondirectional iridescent) green, head with traces of buff, the shade of green becoming slightly darker caudally. Inner rectrices (R1) short, barely projecting beyond green uppertail coverts, dark green on outside vane, white on inner vane. R2 is highly distinctive: greatly elongated, with a black tip and black outer vane, white inner vane. R3, R4, and R5 are consecutively shorter, each black with the tip outlined in white. Remiges dusky. Loral and orbital regions dark green, with a small white postocular spot. Throat and neck (gorget) brilliant iridescent magenta in direct light, turning to cyan and then black as viewing angle changes. Gorget often contains individual non iridescent feathers apparently retained from an alternate molt. Gorget confined to head and rounded at the corners, i.e. lacks elongated 'tails'. Breast off white to light gray, forming a white collar around the gorget but that does not reach dorsal surface. Flanks merging gradually from green dorsally to gray/white on belly, sometimes tinged with a trace of buff (beige) fringes. Femoral tufts and undertail coverts white.

Alternate plumage not described. According to Mobbs (1982) (who observed captive hummingbirds), males undergo an eclipse molt after the breeding season, losing both iridescent gorget and elongated tail streamers. This eclipse molt would explain one specimen of a male taken in January, observed by Zimmer (1953) to have a dull whitish throat and a badly frayed adult tail. Breeding plumaged males caught in Chile in September 2010 often had a couple individual non iridescent gorget feathers (CJC), apparently retained from the prior eclipse plumage (see Molts).


Adult female: Similar to male, with the following exceptions: faint beige tinge throughout plumage, including in green of dorsal surface, throat, flanks; lacks gorget, throat cream, often with a trace of beige and few to no flecks of darker feathers; upper breast less white than male, with traces of beige; tail not greatly elongated, R1 off white basally, distally bronzy green on outer web, inner web grading from light proximally to nearly black distally. R2 longest with a white spot on proximal inner vane and tip, dark black elsewhere. R3 with white on both proximal inner and outer vane tip, black elsewhere, and R4 and R5 black except for white tip.

Immature male: Similar to adult female, except with buff (beige) fringe to body feathers and corrugations on the ramphotheca, up to ~6 months of age (Yanega et al. 1997).

Immature female: No descriptions available

Hybrids: Clark et al. (2013) describe the morphology, displays, and vocalizations of an adult male hybrid between Peruvian Sheartail and Chilean Woodstar (Eulidia yarrellii).

Molts

Adult male Peruvian Sheartails are reported to have an eclipse plumage (Johnson and Goodall 1967, Mobbs 1982) in which the iridescent gorget is largely or entirely replaced by dull white or gray feathers. Zimmer (1953) reports a male collected in May had a tail feather in sheath, while a male collected in January had a badly frayed adult tail (i.e. to be molted soon) and a mostly white throat (i.e. had already gone through eclipse molt). Several close relatives (e.g. Short-tailed Woodstar Myrmia micrura) also appear to molt into an alternate gorget plumage (Clark unpublished observations).

In sum, these data suggest basic molt might occur in adults shortly after austral spring breeding season (i.e. December?); alternate molt likely occurs right before breeding season (i.e. finishing in August). These are guesses are based on observations of individuals with apparently fresh gorget feathers but worn rectrices in early September Some individual males observed in September appear to retain individual non iridescent gorget feathers from previous alternate plumage.

Other patterns of molting are not known to differ from the general hummingbird pattern (e.g. Stiles 1995).

Bare Parts

Iris: dark brown

Bill: dull black

Toes: dusky

Measurements

Table 1.  Morphological measurements of adult Peruvian Sheartail, Chilean Woodstar, and a hybrid male (mean ± s.d, range).  From Clark et al. 2013, van Dongen et al. 2013.

 

Thaumastura cora

Hybrid

Eulidia yarrellii a

 

male (12)

female (6)

Male (1)

male (8)

female (27)

Body mass (g)b

2.5 ± 0.2 [2.3-2.8]

2.6 ± 0.2

2.45

2.3 ± 0.2 [2.0-2.8] (10)

2.3 ± 0.2 (40)

Folded wing chord (mm)

38.8 ± 0.9 [37.5-40.8]

42.9 ± 1.6

37.2

31.5 ± 1.1 [30.4 – 34.2]

36.7 ± 1.0

Exposed Culmen (mm)

16.4 ± 0.5 [15.6-17.5] (19)

17.6 ± 0.6 (35)

15.2

14.8 ± 0.4 [14.3 – 15.5]

15.7 ± 0.6

R1 (mm)

13.7 ± 1.2 [12.0 – 15.4]

26.6 ± 1.4

17.6

14.6 ± 0.5 [14 - 15]

23.7 ± 0.9 (25)

R2 (mm)

89.8 ± 7.7 [75.5-97.2]

32.5 ± 1.7

42.8

24.6 ± 1.0 [23 – 26]

25.8 ± 0.9 (25)

R3 (mm)

45.4 ± 5.2 [33.6-55.6]

30.4 ± 1.2

45.1

30.5 ± 1.0 [29 – 32]

25.1 ± 1.3 (25)

R4 (mm)

33.0 ± 3.2 [25.9-37.9]

25.8 ± 1.6

41.3

30.6 ± 1.0 [29 – 32]

23.9 ± 1.2 (25)

R5 (mm)

24.5 ± 1.8 [20.4-28.0]

22.1 ± 1.4

30.8

30.0 ± 1.0 [29 – 31]

21.2 ± 1.7 (25)

Hovering Wingbeat frequency (Hz)c

49 ± 4.6 (9)

42 ± 2.7 (5)

51.5

64.3 ± 2.0 (2)

52.4 ± 1.0 (3)

                 

 

Recommended Citation

Clark, Christopher J. 2013. Peruvian Sheartail (Thaumastura cora), version 1.0. In Neotropical Birds Online (T. S. Schulenberg, editor). Cornell Lab of Ornithology, Ithaca, New York, USA. https://doi.org/10.2173/nb.pershe2.01