Mangrove Swallow vs Grey-breasted Martin

The white supraloral streak of the Mangrove Swallow is a key distinguishing feature from the Grey-breasted Martin, which lacks this mark. Both species have white underparts, but the Mangrove Swallow's upperparts are nearly black with a green-blue gloss, while the Grey-breasted Martin has a more uniform greyish tone.

Look for the white supraloral streak on the Mangrove Swallow, which is absent in the Grey-breasted Martin. Note the gloss on the Mangrove Swallow's upperparts, which can appear green-blue or steel-blue depending on wear.

The Mangrove Swallow has nearly black upperparts with a green-blue gloss, transitioning to steel-blue with wear, and a distinctive white supraloral streak. In contrast, the Grey-breasted Martin has a more uniform greyish tone on its upperparts and lacks the white supraloral streak.