Tree Martin | Petrochelidon nigricans

Voice

A dry, thin, rattling chirp, drrt or prrit, repeated continuously by the whole flock; it is a harder and less musical sound than the clear chirping of the Welcome Swallow and is often the first thing to betray a flock high above the forest. At the colony this becomes a running, rather peevish chatter in which individual birds cannot be picked out. The song, if it deserves the name, is a soft sustained bubbling twitter without clear strophes, given from a branch by the nest hollow. The alarm is a sharp tschik, and a flock that sees a hawk does not fall silent but grows louder.

Identification

A small stocky swallow of twelve to fourteen centimetres with broad triangular wings and a short tail carrying at most a shallow notch — the silhouette is blunt and compact, with no point behind at all. Crown and back are glossy blue-black, the forehead bearing a small dull rusty patch barely visible at range. The character that counts is the rump: dull off-white to pale grey-buff, a matt pale band between the dark back and the black tail, but without a sharp edge and without clean white. The underside is dirty white to pale grey with a finely streaked, often grubby throat; the undertail coverts are dark. Male and female are alike; young birds are dull brown-black above with pale feather fringes and a faint forehead.

Confusion species

Fairy Martin (Petrochelidon ariel) is the species it shares a flock with almost daily, and the difference lies in head and rump: the Fairy Martin has a wholly chestnut crown and nape and a clean white, sharply bounded rump, while this species has a blue-black crown and a dull, ill-defined rump. The Fairy Martin is besides noticeably smaller and lighter and has a finely white-streaked nape. Welcome Swallow (Hirundo neoxena) has a dark rump, a deeply forked tail with white spots and a rusty throat. Barn Swallow (Hirundo rustica) adds a full blue-black breast band. A swift such as the Fork-tailed Swift (Apus pacificus) also shows a pale rump but is far larger, sickle-winged, and never settles on a wire or branch. In case of doubt: blue-black crown plus dull rump settles it.

Habitat

Dry sclerophyll forest and woodland with old trees full of hollows is the core, together with the river red gum forest along creeks and rivers, where heavy hollow limbs supply the best nest sites on the continent. Beyond that the species is found over pasture and grazing land, over lakes, pools and reservoirs, and in good measure in village and town, where it accepts eaves, cavity walls, bridges and even light towers as nest sites. What it needs everywhere is a hollow with a narrow entrance and open air to hunt above; closed rainforest and treeless desert are avoided. Hunting is done higher than in most swallows, often tens of metres above the canopy.

Range and movements

Virtually the whole of Australia including Tasmania, except the core of the sand dune deserts, and besides that as a breeding bird on Timor and some neighbouring islands of the Lesser Sundas. The picture is that of a migrant within the continent: the birds of Tasmania and the south-east leave the breeding grounds in March and April and move north, some reaching New Guinea and Indonesia, returning in August and September. In northern Australia the species is therefore present all year, but with a strongly shifting composition. In New Zealand it is an irregular visitor, with an occasional breeding attempt in the Bay of Plenty; those cases were not checked against New Zealand Birds Online in this round.

• Resident
• Breeding (summer)
• dark = core range, pale = thinly spread

Where and when to look

Look up. This species hunts higher than the other swallows and is therefore systematically overlooked; whoever looks at thirty metres will find it above virtually any patch of old eucalypt forest. In a mixed flock the rump cannot be seen from below in side light — pick the bird up in a turn of its flight, when it shows its back for a moment. In spring the colony is the quickest route: find an old gum full of hollows and watch for the birds shooting in and out of a slit. The rattling call carries far and is on its own enough to establish the species once it is known.

Conservation

Not threatened: the species is widespread, numerous and flexible in its choice of nest site, and it has settled in with people on bridges, buildings and water engineering without difficulty. The vulnerable side lies in the hollows. Old hollow eucalypts have become scarce in the farming country of south-eastern Australia through the clearing of dead wood and the failure of replacement, and hole-nesters there compete besides with the introduced starling and with introduced honeybees, which occupy the same hollows. Where nest boxes and the retention of standing dead trees form part of management, this species benefits along. Nationally there is no worrying trend.

Scientific name

Petrochelidon nigricans | (Vieillot, 1817)

Vieillot described the bird in 1817 as Hirundo nigricans, from material recorded as 'New Holland' but traced to Tasmania; because the species now sits in another genus, author and date are bracketed. The epithet nigricans is Latin for 'blackish', after the dark upperside. The genus Petrochelidon was introduced by Cabanis in 1850 from Greek petros, 'rock', and chelidon, 'swallow' — the rock swallows, named for the habit of most species in the genus of nesting on cliffs, which is exactly what this species does not do. The English Tree Martin and the Dutch Australische boomzwaluw take instead precisely the telling behaviour, the tree hollow; the Spanish golondrina arborícola does the same.