Although the number of tail feathers is quite variable across groups of birds, the most common number is 12. The left and right tail feathers are mirror images of each other. The outermost tail feather is highly asymmetrical (narrow outer vane, broad inner vane). The feathers become more symmetrical toward the center, with the two central tail feathers usually exactly symmetrical (vanes on both sides of the shaft equal in width). There is a similar change in the curvature of the tail feather shafts from outer to central, with the shafts of the outermost tail feathers usually strongly curved, gradually straightening toward the center, with the central tail feathers shafts completely straight.
Groups of birds can have certain tail feather traits in common. For instance, the tail feathers of most waterfowl are short (although the pictured female Hooded Merganser’s are relatively long), while many gamebird tail feathers are used in display and thus are boldly patterned and/or elongated. Woodpecker tail feathers have pointed, stiff tips that the birds use to brace themselves against tree trunks. Even within a group, such as waterfowl, there can be specific tail traits such as the drake Northern Pintail’s long twin tail feathers and the drake Wood Duck’s squared-off tail feathers.
Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.