What is the defining characteristic of the Canada Warbler's breeding habitat?

Answer

The presence of a dense, low layer of shrubs and saplings (the understory)

The existence of a dense, low layer of vegetation is the defining feature of their breeding habitat, as it provides cover for nesting and suitable foraging perches.

What is the defining characteristic of the Canada Warbler's breeding habitat?
behaviorbirdornithologywildlifewarbler