Rock martin

Appearance

The rock martin of the nominate subspecies "P. f. fuligula" is 12–15 cm long with earth-brown upperparts and a short square tail that has small white patches near the tips of all but the central and outermost pairs of feathers. It has a cinnamon chin, throat, upper breast and underwing coverts, with the rest of the underparts being a similar brown to the upperparts. The eyes are brown, the small bill is mainly black, and the legs are brownish-pink. The sexes are similar in appearance, but juveniles have pale edges to the upperparts and flight feathers. The other subspecies differ from the nominate form as detailed above.

The rock martin's flight is slow, with rapid wing beats interspersed with flat-winged glides, and it is more acrobatic than the larger Eurasian crag martin. It is a quiet bird; the song is a muffled twitter, and other calls include a "trrt" resembling the call of the common house martin, a nasal "vick", and a high pitched "twee" contact call.

The rock martin is much drabber than most African swallows, and confusion is unlikely except with other crag martins or with sand martins of the genus "Riparia". The pale crag martin is smaller, paler and greyer than its southern relative. Although only slightly larger than the sand martin and brown-throated sand martin, the rock martin is more robust, has white tail spots, and lacks a breast band. It is paler on the throat, breast and underwings than the all-dark form of the brown-throated sand martin.

Naming

There are several subspecies differing in plumage shade or size, although the differences are clinal, and races interbreed where their ranges meet. The small, pale former subspecies found in the mountains of North Africa, the Arabian peninsula and southwest Asia are now normally split as a separate species, the pale crag martin, following German ornithologist Jean Cabanis, who first formally described these birds, but the changes in size and colour are continuous, and the forms often intergrade where they meet, so the evidence for separate species is not strong. The southern forms of the rock martin can weigh more than twice as much as the smallest northern subspecies of pale crag martin. The average weight for "P. f. fusciventris" is 22.4 g against 10 g for "P. o. obsoleta". The robust, large-billed southernmost forms are sufficiently different from dark, fine-billed "P. f. fusciventris" that the latter could also be regarded as a potentially different species. However, Rhodesian ornithologist Michael Irwin collected specimens from southern Zimbabwe which were dark above like "P. f. fusciventris" and rich reddish below like "P. f. fuligula". This led him to suggest that the two groups had previously been isolated, but were probably hybridising following secondary contact.

Distribution

The rock martin breeds in suitable habitat in Africa north to Nigeria, Chad and Ethiopia. It is largely resident apart from local movements or a descent to lower altitudes after breeding. This species has been recorded as a vagrant in Gabon, and its status in Congo is uncertain.

Status

The rock martin has a very large range of 9.5 million km2. The total population is unknown, but the bird is described as generally common, although scarce in Botswana and Namibia. The population is thought to be stable, mainly due to the absence of evidence of any declines or substantial threats. Its large range and presumably high numbers mean that the rock martin is not considered to be threatened, and it is classed as least concern on the IUCN Red List.

Habitat

The natural breeding habitat is hilly or mountainous country with cliffs, gorges and caves up to 3,700 m above sea level, but this martin also breeds in lowlands, especially if rocks or buildings are available, and may be found far from water. It readily uses man-made structures as a substitute for natural precipices.

Reproduction

Rock martin pairs often nest alone, although where suitable sites are available small loose colonies may form with up to 40 pairs. These martins aggressively defend their nesting territory against conspecifics and other species. Breeding dates vary geographically and with local weather conditions. Two broods are common, and three have been raised in a season. Breeding mainly August to September. The nest, built by both adults over several weeks, is made from several hundred mud pellets and lined with soft dry grass or sometimes feathers. It may be a half-cup when constructed under an overhang on a vertical wall or cliff, or bowl-shaped like that of the barn swallow when placed on a sheltered ledge. The nest may be built on a rock cliff face, in a crevice or on a man-made structure, and is re-used for the second brood and in subsequent years.

The clutch is usually two or three buff-white eggs blotched with sepia or grey-brown particularly at the wide end. The average egg size in South Africa was 20.8 x 14.1 mm with a weight of 2.17 g. Both adults incubate the eggs for 16–19 days prior to hatching and feed the chicks about ten times an hour until they fledge and for several days after they can fly. The fledging time can vary from 22–24 days to 25–30 days, though the latter estimates probably take into account fledged young returning to the nest for food.

Food

The rock martin feeds mainly on insects caught in flight, although it will occasionally feed on the ground. When breeding, birds often fly back and forth along a rock face catching insects in their bills and feed close to the nesting territory. At other times, they may hunt low over open ground. The insects caught depend on what is locally available, but may include mosquitoes and other flies, Hymenoptera, ants and beetles. This martin often feeds alone, but sizeable groups may gather at grass fires to feast on the fleeing insects, and outside the breeding season flocks of up to 300 may form where food is abundant. Cliff faces generate standing waves in the airflow which concentrate insects near vertical areas. Crag martins exploit the area close to the cliff when they hunt, relying on their high manoeuvrability and ability to perform tight turns.

A study of nine bird species including four hirundines showed that the more young there are in a nest, the more frequent are the parents' feeding visits, but the visits do not increase in proportion to the number of young. On average a solitary nestling therefore gets more food than a member of a pair or of a trio. Since the nestling period is not prolonged in proportion to the drop in feeding rate, an individual fledgling from a larger brood is likely to weigh less when it leaves the nest. However, a subspecies of the rock martin was an anomaly in respect of both feeding rate and nestling time. There was no difference in parental feeding rate for members of a pair and members of a trio, but the nestling period averaged 1.5 days longer for trios than pairs.

Predators

Some falcons have the speed and agility to catch swallows and martins in flight, and rock martins may be hunted by species such as the peregrine falcon, Taita falcon, African hobby and wintering Eurasian hobby. Rock martins often share their nesting sites with little swifts, which sometimes forcibly take over the martin's nests. In 1975, one of the first findings of the tick "Argas africolumbae" was in a nest of "Ptyonoprogne f. fusciventris" in Kenya, at that time the martin was described under its synonym "Ptyonoprogne fuligula rufigula".