The Vervain Hummingbird has a protracted breeding season with nests reported in late December through early August (table 2). According to March (1863), the species breeds year-round, but this may be an exaggeration, for no authors report nests in Sept., Oct., Nov., or early Dec. (table 2). A female collected 29 July, 2004 in the Blue Mountains had a greatly enlarged ovary, and another female collected 14 August 2004 had an ovary that was not quite as large and may have been regressing (possibly indicating the end of the breeding season; CJC). More information on the seasonality of breeding would be valuable. It seems likely that females produce multiple clutches per year, but no direct information on this is available.
The nest is a minute cup, lined interiorly with hair, seed fuzz, wool, plant down, or other soft material, and with lichen or moss attached to the outside for camouflage (see photos on p. 156 of Tyrrell & Tyrrell 1990) (Christy 1897; Griswold 1960; Wetmore and Swales 1931). Spiderweb is extensively used to hold the nest together, and to anchor it. Nests are often within 1m of the ground (Wetmore and Swales 1931), often in an inconspicuous location on the branch of a tree, bush, or bamboo (Gosse 1847).
Eggs are always two in number, white, and measure 11.6 x 8.3 mm (n = 2, Bond 1928). When laid they weigh 0.38 g (n = 3) (Lack 1976), and are laid on successive days (Pearson 1971). Lack (1976) and Pearson (1971) indicated that eggs are incubated for 16 or 17 days (n = 4 nests) and (Miller 1969) reported an incubation time of 19 days; secondary reports that incubation lasts 12 days (Tyrrell and Tyrrell 1990; Wetmore and Swales 1931) appear to all originate from Vieillot’s (1802) unreliable description (citation in Wetmore and Swales 1931). Vieillot also claims that males perform incubation (Wetmore and Swales 1931), whereas male contributions to nesting are not mentioned by any of the careful observations of nests (e.g. Griswold 1960; Miller 1969; Paterson 1973; Pearson 1971; Pomeroy 1970). It therefore appears that only the female participates in nesting and rearing the chicks, as is the case in related species.
Nestlings hatch naked, weighing 0.315 g (n = 3) (Lack 1976), and at first the mother broods the offspring (for ~10 days; Pomeroy 1970) and removes wastes (Paterson 1973), but at about two weeks of age the young eject fecal matter from the nest themselves, by raising their posteriors so as to eject feces over the edge of the nest (Gosse 1847; Griswold 1960; Paterson 1973). Fledging occurs at approximately 21 days (range: 19-22; n = 13 nestlings) (Lack 1976; Paterson 1973; Pearson 1971; Pomeroy 1970) or even 25 days (Miller 1969). Miller (1969) also reports a severe storm, which may have deprived the nestling of food for a couple of days, thereby delaying their development. The two young often fledge asynchronously, with one individual leaving the nest up to three days before the other (C. Rimmer pers. comm., Lack 1976, Paterson 1973). When one offspring is fledged and the other is not, the fledged young remaining in the vicinity of the nest while the female cares for both offspring. The female feeds her offspring a combination of insects and nectar; the proportions of each are unknown and it is possible that juveniles are fed primarily insects. Food is swallowed by the female and then regurgitated for the offspring, which gape for food, but might not produce any begging vocalizations, for this detail is not mentioned in detailed accounts like that of Griswold (1960). It is unknown how long juveniles are dependent on their mother after fledging.
|# of nests||2||2||7||3||1||1||2||2||0||0||0||2|
Each individual report of an active nest (or gathering of nesting material), by month. Tallied from various references (C. Rimmer pers. comm., CJC unpubl. data, Sallé -- cited in Wetmore & Swales 1931; Bond 1928; Christy 1897; Diamond 1974; Gosse 1847; Miller 1969; Paterson 1973; Pearson 1971; Pomeroy 1970; Wetmore and Swales 1931). This chart does not account for observer bias such as if more observers have taken note of the Vervain’s behaviors during December - August.