Abstract
F ew groups of birds are more characteristic of the neotropics than are the motmots, members of the coraciiform family Momotidae, which is distributed from northern Mexico south to northern Argentina and southern Brazil. Motmots are robust birds with a distinctive overall appearance that comes from a broad head with a proportionately long, stout bill, as well as proportionately long tarsi and, in most species, an acutely gradated tail with elongated central feathers.
It is the shape and structure of the tail, probably more than any other feature, that typifies the motmots and attracts most interest. In some species and subspecies, the elongated central tail-feathers are denuded subterminally, with the fully intact tips forming flaglike spatules. When newly acquired through molt, the central tail-feathers are without bare subterminal shafts, so it has been claimed that the birds deliberately strip away the barbs by passing each feather through the bill. However, a foremost expert on neotropical birds, Alexander Skutch, points out that along the narrower subterminal portion of each feather the barbs are loosely attached and so fall away as the bird preens and probably also in consequence of the tail rubbing against vegetation. My examination of museum specimens supports the explanation put forward by Skutch, but suggests also that feather growth is well advanced before the barbs will fall away, and then they will do so all at once. In the American Museum of Natural History, New York, there is a specimen of the Blue-crowned Motmot Momotus momota with barbs stripped from much of the subterminal shafts of the central tail-feathers, and this specimen was collected at the same locality and only 18 days later than a specimen without bare subtenninal shafts.
Widespread with Subspeciation
The most widespread, and probahly the most familiar species is the Bluecrowned Motmot, which ranges from eastern Mexico south to northern Argentina, and is present also on Trinidad and Tobago, in the West Indies. Approximately 45 cm in length, adults are predominantly rich olivaceous green with hlack on the crown and a broad hlack facial hand from the base of the hill and surrounds of the eye to the ear-covens, where it is hordered above hy a narrow line of brilliant pale blue. The forehead to forecrown is brilliant silvery blue, and on sides of the crown this meets a band of deep violet-hlue extending to the occiput and so encircling the hlack crown. A prominent russet patch is present on the nape, and at the centre of the upper hreast there are one or more elongated tufts of black feathers bordered hy bright pale blue. 111e tail above is dark green, becoming deep blue to black on spatules at the end of subterminally hare central feathers. The hill is grey-black, the iris dark red, and the legs brownish-grey. Juveniles are noticeably duller than adults, having the forehead dusky greyish-brown tinged with hluish-green and with narrower superciliary hands of paler blue, while there are no tufts of hlack feathers on the breast and non-elongated central feathers of the markedly shorter tail are without hare suhterminal shafts; there is a prominent pale tip to the hill and the iris is brown.
This description is of the nominate subspecies occurring in northern South America, from the Orinoco River east to the Guianas and south to southern Venezuela and the north hank of the Amazon River in north-eastern Brazil. Geographical variation is quite pronounced through the extensive range, with some 20 subspecies being recognized, mainly because of the extent of blue on the crown or rufous on the underparts. More divergent subspecies include M. m. coeruliceps from eastern Mexico, which has the crown entirely blue, and M. m subrufescens from the Caribbean coast of northern South America, which has the underparts and nape to mantle rich tawny-chestnut. Similar, though larger birds from the subtropical to lower temperate zones of the Andean cordilleras in western Colombia to eastern Peru are recognized as a separate species, the Equatorial Motmot Momotus aequatorialis.
Overlooked in the Forest
Though preferring moist lowland forests, the Blue-crowned Motmot ranges up to about 1800 m in the foothills or uplands, and is found in a variety of wooded habitats, even coming into arid areas by following gallery forests along watercourses. It is generally common, hut may he locally scarce, especially in districts where there is competition from the larger Barypbthengus motmots. Along the lower Mahaicony River, in Guyana, I encountered it in disturbed forest and old secondary growth, but it was not plentiful.
Quiet and unobtrusive during much of the day, these motrnots can he overlooked as they sit on shaded perches in the lower branches of forest trees, the predominantly green or rufous plumage blending with...