Blue-billed teal

Adult males have dark brown crown contrasting with paler face, throat, breast and side except for a blackish thumb-shaped patch on the ear region.[8] The back of the neck is spotted with black and this spotting extends down through the neck and become intensively spotted on the breast, the spots appear to be larger and less obvious on the light brown flanks and abdomen, and the posterior underparts and under tail coverts becoming vermiculated with black.[8] The scapulars and tail are dark brown to black, the upper wing surface is blackish as well, with the coverts giving a greenish gloss.[8] An iridescent green speculum exists on the secondaries, bounded posteriorly by narrow black and terminal white bars.[8] The iris is brown, the legs and feet are bluish gray, and the bill is light bluish gray with a blackish culmen and nail.[8]

Females have browner crowns, they have less contrasting facial markings and more rounded scapulars, the under tail coverts are not vermiculated, and the wing is less glossy and colorful than that of an adult male.[8]

Juveniles resemble adult females but are duller throughout the body and less distinctively marked with spots.[8][10] Ducklings have grayish brown underparts and yellowish grey below, the cheeks is paler with pinky puff wash and grey-brown ear patch.[10]

See External Links for duck external anatomy.

The blue-billed teal was described as the smallest known duck by D. D. Thomas and J. B. Condy in 1965.[11]

• Length: 330–350 mm[10]
• Weight: 53-288 g[8][10]
• Wing: 147–157 mm[10]
• Tail: 55–66 mm[10]
• Bill: 32–42 mm[10]
• Eggs: 43×33 mm in average, creamy, 25 g[8]

The blue-billed teal prefers feeding at muddy edges, it will also feed on lands and flooded fields like rice paddies, and in waterside that is disturbed heavily by livestock.[10] It feeds in well-vegetated areas by dabbling, swimming or on foot.[10] No diving during foraging is recorded.[8] It is omnivorous,[10] although its diet consists mainly of grass seeds, especially of the grass Sacciolepis,[8] however it may also consume aquatic invertebrates almost exclusively such as crustaceans like ostracods, molluscs, water insects such as beetles and their larvae, if these are super abundant.[8][10]

Molt is poorly understood in the blue-billed teal, there is no identified eclipse plumage in males, but breeding males are much brighter than females and the breast spots are more distinct.[10]

Both sexes produce series of clicking notes, given as harsh ke-ke-ke when they are disturbed, during flying or within flock.[10] Males produce a highly distinctive wooden rattling call that sounds like a mechanical rattle, while the female has a typical quack and a decrescendo call of only a few notes.[10]

The breeding behavior of the blue-billed teal is relatively undemonstrative. Based on current research, the bond of blue-billed teal does not extend beyond the female's incubation period, suggesting the bond is presumably reestablished annually.[8] Although majority of breeding is observed in summer, this species also breed in winter, and thus courtship behavior can be seen throughout the whole year.[8] The most common display in this species is the combination of female inciting and male turning the back of the head.[8] Female blue-billed teal incites males by doing lateral movements silently or nearly silently, and males usually respond by swimming ahead and turning the back of the head.[8] However, the males may respond by drinking, they raise their neck vertically and produce a soft mechanical series of call notes (burping) and they sometimes combine these two displays in a burp-drinking order.[8] Moreover, during social display, the duck frequently perform a wing-flapping and both-wing-stretch sequence of behavior that seems to be a significant part of the display.[8] Pre-copulatory behavior consists of mutual head pumping, and post-copulatory display by the male may vary from no perceptible activity to a swimming shake, wing flapping, or burping.[8] The female most usually only bathes after copulation.[8] The cluster size for this species ranges from 6 to 8 eggs with 7 being the most frequently encountered number.[8] However, based on Clark's observation on the Witwatersrand, the ducklings in families ranges from 1 to 7 with 3 predominating.[15] Incubation period ranges from 25 to 27 days for naturally incubated clutches.[8] The male may remain nearby as the female incubates, but there is no indication of further male participation in brood rearing.[15] So far as is known, the species is not multiple-brooded, although nest failure may lead to re-nesting.[8]