Dusky crag martin

Appearance

The dusky crag martin is 13 cm long with a broad body, wings and tail. It has sooty-brown upperparts and slightly paler underparts, with a streaked pale dull rufous chin, throat and foreneck. The tail is short and square, with small white patches near the tips of all but the central and outermost pairs of feathers. The underwing coverts are dark brown, the eyes are brown, the small bill is mainly black, and the legs are brownish-pink. The sexes are alike, but juveniles have rufous grey tips to the plumage of the upperparts and wings. This species can be distinguished from the Eurasian crag martin and rock martin by its darker underparts, and its white tail spots are significantly smaller than those of the Eurasian crag martin. The under-tail coverts are of the same shade as the underside of the abdomen but these are darker in the Eurasian crag martin.

This small martin's flight is typically slow and leisurely, but it is capable of considerable speed when required. The calls are similar to those of the Eurasian crag martin and include a soft ''chi, chi'' contact call and a twittering song.

Distribution

The nominate subspecies of the dusky crag martin breeds in much of the Indian subcontinent from the base of the Himalayas south to the Nilgiri mountains and east to West Bengal, and ''P. c. sintaungensis'' is found in southwestern China, and the northern parts of Thailand, Vietnam and Laos. The dusky crag martin is largely resident apart from local movements after breeding, but it has bred in Malaysia at least once, and occurred as a vagrant to Sri Lanka and probably Borneo.

The natural breeding habitat is hilly or mountainous country with cliffs, gorges and caves, with nesting typically up to an altitude of about 1,800 m , although up to 2,000 m in Thailand. This martin also breeds in lowland areas utilising man-made structures as a substitute for natural precipices. Stone buildings such as old forts are particularly favoured, and the dusky crag martin can be found in urban areas including Mumbai. Nests on buildings can be 30 m from the ground, and include unusual sites such as light fittings.

Status

The total population of the dusky crag martin has not been quantified, but it is suspected to be increasing owing to the availability of artificial nest sites. This martin is locally common in India, Thailand, and southern China, and there appear to be range extensions to the northeast into Guangxi, southwards into lowland Laos, and westwards to the hills and plains of Sindh. There is also a recent unconfirmed report from Cambodia. Its large range and presumed high numbers mean that the dusky crag martin is not considered to be threatened, and it is classed as Least Concern on the IUCN Red List.

Habitat

The nominate subspecies of the dusky crag martin breeds in much of the Indian subcontinent from the base of the Himalayas south to the Nilgiri mountains and east to West Bengal, and ''P. c. sintaungensis'' is found in southwestern China, and the northern parts of Thailand, Vietnam and Laos. The dusky crag martin is largely resident apart from local movements after breeding, but it has bred in Malaysia at least once, and occurred as a vagrant to Sri Lanka and probably Borneo.

The natural breeding habitat is hilly or mountainous country with cliffs, gorges and caves, with nesting typically up to an altitude of about 1,800 m , although up to 2,000 m in Thailand. This martin also breeds in lowland areas utilising man-made structures as a substitute for natural precipices. Stone buildings such as old forts are particularly favoured, and the dusky crag martin can be found in urban areas including Mumbai. Nests on buildings can be 30 m from the ground, and include unusual sites such as light fittings.

Reproduction

Dusky crag martin pairs typically nest alone, although in suitable locations several pairs may be quite close to each other. The natural nesting habitat is under ledges on cliff faces or river banks, but man-made structures are readily used. Stone buildings such as old hill forts, mosques and tombs are preferred, and other artificial sites include bridges, archways and culverts. Breeding has been reported in every month, but mainly in February and March, and again after the rains start in July and August; usually two broods are raised. The nest, built by both adults, is an open half-cup made of mud and lined with soft material such as feathers or dry grass. It is constructed under an overhang or in a crevice on a cliff or man-made structure, and is re-used for the second brood and in subsequent years. The clutch is two to four eggs, white with reddish brown blotches particularly at the wide end, and averaging 17.7 x 13.0 mm with a weight of 1.57 g . Both adults incubate the eggs and feed the chicks. Incubation and nestling periods are unknown but assumed to be similar to those of the Eurasian crag martin .

Food

The dusky crag martin feeds mainly on insects caught in flight. When nesting, birds often fly back and forth near to a rock face or building hunting for their prey. This martin is more gregarious outside the breeding season, and may form small flocks where food is abundant. Vertical surfaces are preferred for hunting, and a study of the Eurasian crag martin, which has a similar foraging technique, showed that cliff faces generate standing waves in the airflow which concentrate insects near vertical areas. The martin exploits the area close to the cliff when it hunts, relying on its high manoeuvrability and ability to perform tight turns. When feeding young, foraging is concentrated on the profitable patches in the immediate vicinity of the nest, since there is a negative correlation between foraging distance and feeding rate.

Predators

In addition to predation by birds of prey such as the peregrine falcon, this small martin has been recorded in the diet of the greater false vampire bat, ''Megaderma lyra''.