Purple Martin is vaguely similar but lacks the white rump patch and doesn't usually occupy the same habitat. Shearwaters are much larger. Other storm petrels are very similar. Black, Ashy, and Least storm-petrels lack the white rump. Wedge-rumped storm-petrel is smaller with a larger rump patch. Band-rumped and Leach's storm petrels are larger with different flight styles and their feet don't protrude beyond the end of their tails. Leach's has a forked tail and a divided or absent rump patch. Band-rumped has a thinner rump patch.