The Mascarene martin or Mascarene swallow (Phedina borbonica) is a passerine bird in the swallow family that breeds in Madagascar and in the Mascarene Islands. The nominate subspecies occurs on Mauritius and Réunion and has never been found away from the Mascarene Islands, but the smaller Madagascan subspecies, P. b. madagascariensis, is migratory and has been recorded wintering in East Africa or wandering to other Indian Ocean islands.
Adult Mascarene martins of the nominate subspecies are 15 cm long. This small hirundine has dark brown-grey upperparts with faint streaking. It has grey-brown underparts becoming white on the throat and lower abdomen, all being heavily streaked with black. The slightly forked tail averages 54.6 mm long and has white edges to the brown undertail coverts. The sexes are similar, but juvenile birds have more diffuse breast streaking, and white tips to the feathers covering the closed wing. The Madagascan subspecies is overall paler and larger-billed than the nominate form. It has denser streaking on the breast, but only very fine lines on the lower abdomen and on the white undertail. It is distinctly smaller than the nominate subspecies, 12–14 cm in length. This martin moults in December and January on Mauritius, and Madagascan breeders wintering on the African mainland moult in June and July.
The Mascarene martin is a relatively quiet bird, but it has a warbled siri-liri siri-liri song given in flight or when perched; some calls given by perched birds end in a glissando. Other vocalisations may be used during mating or displays of aggression. There is a chip contact call, and the young birds produce a fast twittering sound when begging for food. Birds wintering in mainland Africa are usually silent.