For example, Barn Swallow females have been reported to prefer males whose long outer feathers are the same length on each side.
Steve Swallow | Red-rumped Swallow | Swallow the Sun | Swallow | James Swallow | Swallow Tanager | Northern Rough-winged Swallow | White-rumped Swallow | Swallow TP | Swallow This Live | Swallow-tailed Kite | Swallow Sidecar Company | Swallow New Swallow | Long Barn | Ian Swallow | Dutch barn | Yonkers Trolley Barn | Wheeler-Magnus Round Barn | Tithe barn | tithe barn | The Big Swallow | Tell Me What Rockers to Swallow | Swallow This Live: Flesh & Blood World Tour | Swallow Tales | Swallow-tailed Hummingbird | Swallow My Pride | Swallow Falls | Swallow Doretti | Swallow (bird) | Swallow Airplane Company |