Why is confirming the Mourning Warbler's identity by sight often challenging for observers?
Answer
Because they habitually skulk in the densest vegetation
The bird's behavior involves staying low among leaves in thick cover, meaning observers often hear the bird before catching a glimpse of the namesake slate-gray cowl.

Related Questions
What feature primarily gives the male Mourning Warbler its distinctive name?How does the female Mourning Warbler's throat and breast typically appear compared to the male's namesake hood?Despite its somber moniker, how is the Mourning Warbler's song usually described?Which habitat component do Mourning Warblers strongly prefer in their breeding grounds?Where do Mourning Warblers primarily forage for insects?What color provides a striking contrast to the male's dark upper parts?Why is confirming the Mourning Warbler's identity by sight often challenging for observers?What region primarily constitutes the wintering grounds for the Mourning Warbler?How might the male's plumage appear when observed in deep shade?Which area is included in the described North American breeding range of the Mourning Warbler?