Why do swallows line their nests with feathers?
A. The rate of growth and general health of Tree Swallow nestlings is directly related to the number of feathers lining their nests. This may be because of the added insulation the feathers provide, or because the feathers provide a barrier protecting the babies from parasites, or some other reasons not fully understood. But because it is so important to Tree Swallow nesting success, the adults spend a lot of time searching out and gathering feathers. (You can learn more about this in David W. Winkler’s 1993 paper in the Auk (110:29-36), “Use and importance of feathers as nest lining in Tree Swallows (Tachycineta bicolor)”).
