Appearance

A very small hummingbird; only slightly larger than the Bee Hummingbird (Mellisuga helenae) and roughly the same size as other tiny hummingbird species. It is unmistakable in its native range of Jamaica and Hispanola, where it is the only tiny species of hummingbird. Notably, males lack any iridescent feathering, unlike many other hummingbird species, thus the sexes are only slightly dimorphic. Both sexes are green dorsally and pale ventrally, with a short bill and short tail. The best field-characters for determining sex is the adult male’s entirely dark, slightly forked tail, which contrasts with the female’s rounded tail that includes white tips of the outer rectrices. Juvenile males and females are very similar; the immature male’s throat is more flecked with grey than the adult female’s, and there is no known way to distinguish between juvenile and adult females. Due to these similarities in appearance, to be trustworthy, field-observations of behaviors need to account for the similarity between juvenile males and adult females when the observer claims to know the sex of birds observed.

In the field, unmistakable in its natural range due to its minute size. Drabber than many other hummingbirds. It is similar to females and juveniles of the smaller Bee Hummingbird (Mellisuga helenae), but in addition to size, the feathers on the back are more blue-tinged in M. helenae. If only glimpsed, the Vervain could be mistaken for a hawkmoth (Manduca sp) or bumblebee (Bombus sp).

The following descriptions are from Ridgway (1911): “Adult male. – Above dark dull metallic green, darker (sometimes nearly black) on rump and upper tail-covers; tail black, including middle rectrices; remiges dusky, very faintly glossed with purplish; auricular and suborbital regions deep sooty gray; chin throat and chest pale gray, the first two with feathers dusky gray centrally producing a spotted effect; under parts of the body dark metallic green, intermixed along the median line with gray; under tail-coverts dark metallic green narrowly margined with pale gray and with base of feathers grayish; femoral and lumbar tufts white; bill dull black; iris dark brown; feet dusky.”

“Adult females.— Above rather dark metallic green, bluish green or (rarely) bronze-green, including basal two-thirds (approximately) of middle rectrices; lateral and terminal or subterminal portion of middle rectrices black, the outermost broadly, the next less broadly tipped with dull white, the third sometimes narrowly tipped with the same; remiges dusky, faintly glossed with purplish; under abdomen, deepening into sooty grey laterally (especially on auricular and suborbital regions and sides of neck), the sides and flanks glossed with metallic green; bill etc., as in adult male”

“Immature male.—Similar to the adult female but feathers of chin and throat with a darker gray mesial streak, and sides more strongly or extensively glossed with green”.  Bond (1936) adds that the white tips of the outer rectrices are less sharply defined in juvenile males.

Immature females are not mentioned by previous authors, and may not be distinguishable from adult females except by dissection. Unlike other hummingbirds, bill corrugations may not provide as accurate an index of age in this species, because juvenile birds (as determined by plumage and gonads) were captured that had no corrugations on their bills (CJC).

Very little information is available. One individual captured 14 August, 2004 in the Blue Mountains (Jamaica) was molting its rectrices (CJC). It is likely to be similar to relatives, exhibiting one complete molt per year after the breeding season. Subadults (juveniles) appear to have one plumage that resembles the female’s plumage, and they probably molt into their adult plumage in their first molt.

The legs and feet are bare and 'dusky' colored (Ridgway 1911).

Individuals are roughly 6 cm long, which includes the 1 cm bill. The average body mass (as measured with a digital scale with precision of 0.01g) fluctuated around 2.1 g with little obvious difference between the sexes (CJC); other reports may have overestimated body mass if the weighed individual had a full crop of nectar, or was weighed with an imprecise or inaccurate spring-scale. For example, a caged female Vervain weighed 2.38 g before feeding, and 2.83 g just after taking a meal (CJC). Detailed morphological measurements for both subspecies are presented in table 1.

(1) body mass recorded from individuals with no nectar in their crop; masses were measured with a digital scale (Acculab).
(2) muscle mass is the sum of the pectoralis and the supracoracoideus muscle masses
(3) sample sizes for muscle and heart masses are in parentheses.