Appearance

Zimmerius tyrannulets are very small tyrant flycatchers, with short stubby bills. Zimmerius do not have wing bars, but the wing coverts and most remiges are edged with yellow green. Paltry Tyrannulet is a typical member of the genus, with a black bill, gray crown, white supercilium, greenish back, and a lightly striped white breast. This species is best identified by the Zimmerius pattern of its wing feathers, which are all edged with yellow.

The wing pattern is unique throughout most of the range of the species: Paltry Tyrannulet lacks wing bars, and instead has pale edges to the wing coverts and all flight feathers. The yellow leading edge of each feather is wider than the trailing edge. Paltry Tyrannulet overlaps geographically with its congener Golden-faced Tyrannulet (Z. chrysops) in Colombia and Venezuela; Golden-faced Tyrannulet is similar but has a yellowish face and a green (not gray) crown. Paltry Tyrannulet otherwise is most likely confused with some Tolmomyias flycatchers (especially Yellow-olive Flycatcher T. sulphurescens), but Tolmomyias species are larger bodied, with a much larger and broader bill, and tend to have pale lores and pale mandibles. In Central America, Slate-headed Tody-Flycatcher (Poecilotriccus sylvia) has similar wings but with additional yellow wing bars, and a larger bill. Some elaenias (Elaenia spp.) may show similar wing patterns, but they are larger birds with an upright stance, and typically have a bicolored bill as well as a crest. Olivaceous Flatbill (Rhynchocyclus olivaceus) has similar overall colors and wing pattern, but is much larger, has an eye ring, and distinctive larger, broad bill.

Adult: In Central American populations (vilissimus and parvus; includes Colombia along the Panama border), the upperparts are olive green, except the crown is grayish, and there is a moderate, short whitish supercilium. Primaries, secondaries, tertials, and upperwing coverts are edged in yellow, and the leading margin of each of these feathers is more substantial than the tip and trailing edge. Significantly, there are no wing bars. Underparts are off white, with indistinct light streaks on the breast. A weak yellow wash may be visible on the belly and undertail coverts. The tail is narrow and long (as compared to other small tyrannids), and is dark gray. The sexes are identical, though tail length is shorter in females (Restall et al. 2006a). See also Ridgway (1907) and Wetmore (1972); and see Geographic Variation for comments on South American taxa.

Immature: Similar to adult, but with brown irides, an olive gray crown, broader but indistinct wing edgings, and yellow tinge in the supercilium (Stiles and Skutch 1989, Restall et al. 2006a).

Nestling: Skutch (1960) described the appearance of freshly hatched nestlings in Costa Rica as having pink skin covered with long, gray down, and bright yellow bare parts.

Molts of Paltry Tyrannulet apparently are undescribed.

Iris: light brown, brownish white, or grayish white in Central American populations, and darker in South American populations (Dickey and van Rossem 1938, Wetmore 1972, Stiles and Skutch 1989, Restall et al. 2006a).

Bill: the short, narrow, rounded black bill is unusual among flycatchers; Skutch (1960) noted that its shape recalls the bills of chickadees (Poecile, Parus, etc.).

Tarsi and toes: black, brownish black, or dark gray (Dickey and van Rossem 1938, Wetmore 1972); the tarsi are relatively long for a flycatcher.

Total length: 9.5 cm (Stiles and Skutch 1989; parvus), 11-12 cm (Howell and Webb 1995; vilissimus), 12 cm (Hilty and Brown 1986; improbus group), 12.7 cm (Hilty 2003; improbus group and petersi)

Linear measurements (subspecies parvus; Wetmore 1972):

male (n = 10)

wing length: mean 51.4 mm (range 47.7-55.2 mm)

tail length: mean 42.2 mm (range 39.0-46.7 mm)

bill length (culmen from base): mean 9.4 mm (range 9.0-9.9 mm)

tarsus length: mean 16.1 mm (range 15.6-16.7 mm)

female (n = 10)

wing length: mean 45.2 mm (range 42.5-50.8 mm)

tail length: mean 34.2 mm (range 31.7-37.0 mm)

bill length (culmen from base): mean 9.0 mm (range 8.6-9.7 mm)

tarsus length: mean 14.5 mm (range 13.9-15.0 mm)

Mass:

parvus, mean 9.5 g ± 0.7 g (n = 4; Leck 1975); mean 9.8 g ± 0.9 g (n = 11; Leck 1975); 8.5 g (n = ?, range?; Stiles and Skutch 1989)

improbus, 10.9 g (n = ?, range?; Hilty 2003)