Monday, May 4, 2015
Tricks of the Trade #1: telling Bank and Rough-winged Swallows without seeing their throats
For the last few weeks, I have been seeing Northern Rough-winged Swallows zipping along the flooded batture of the Mississippi River. Most were identifiable without seeing the species' classic field mark, the brown-washed throat that separates it from Bank Swallow- which sports a brown neck ring. How?
Because they are both brown-backed, short-tailed, and give similar grating vocalizations, these two species are more easily confused with each other than with any other swallow. Even if you can't see the throat, with practice a couple other differences will almost always enable a correct identification: 1) the Roughwing is slightly larger, appearing less "compact" than Bank; 2) the back and fore wing (wing coverts) of the Rough-winged are warmer brown, contrasting with the slightly darker rest of the wing; the Bank is more uniformly dark brown above.
These marks are insufficient for identifying these birds outside of their normal range or season- for that, you need the throat. But for sorting through a flock or making rapid assessments, they are very useful distinctions.
It will also help that from mid May through July, only Rough-wings will be in southeast Louisiana- Banks do not nest here.