▁birds ▁are ▁generally ▁smaller ▁and ▁have ▁dark er ▁grey ▁crow ns . ▁ ▁War bling ▁v ire os ▁for age ▁for ▁insect s ▁in ▁trees , ▁ho pping ▁along ▁branches ▁and ▁sometimes ▁hover ing . ▁They ▁also ▁eat ▁ber ries , ▁especially ▁before ▁migration ▁and ▁in ▁winter ▁qu arters , ▁where ▁they ▁are ▁– ▁like ▁other ▁v ire os ▁– ▁apparently ▁quite ▁fond ▁of ▁g um bo - lim bo ▁se eds , ▁though ▁they ▁will ▁not ▁vent ure ▁into ▁human - mod ified ▁habitat ▁to ▁get ▁them . ▁They ▁make ▁a ▁deep ▁cup ▁nest ▁susp ended ▁from ▁a ▁tree ▁branch ▁or ▁shr ub , ▁placed ▁relatively ▁high ▁in ▁the ▁east ▁and ▁lower ▁in ▁the ▁west . ▁The ▁male ▁helps ▁with ▁inc ub ation ▁and ▁may ▁sing ▁from ▁the ▁nest . ▁ ▁The ▁war bling ▁v ire o ' s ▁song ▁is ▁a ▁cheer ful ▁war ble , ▁similar ▁to ▁that ▁of ▁the ▁painted ▁b un ting . ▁There ▁are ▁subt le ▁differences ▁in ▁song ▁between ▁eastern ▁and ▁western ▁birds , ▁at ▁least ▁where ▁the ▁ranges ▁meet ▁in ▁Al berta . ▁Some ▁authorities ▁split ▁the ▁eastern ▁and ▁western ▁races ▁of ▁this ▁species ▁into ▁separate ▁species : ▁The ▁western ▁war bling ▁v ire o , ▁V . ▁sw ain son i , ▁includes ▁V . ▁g . ▁sw ain son i , ▁which ▁bre eds ▁from ▁sout he astern ▁Al aska ▁and ▁south western ▁North west ▁Territ ories ▁to ▁the ▁Sierra ▁San ▁Pedro ▁M árt ir , ▁B aja ▁California , ▁and ▁V .