Photo made by J.S. Dunning in Ecuador. Blue in the coastal area, yellow in savanna, red in the forest. The bird leaves in april and returns in august as can be seen in the graph below of the total number of observations of a yellow warbler per month, summed for some years. Number of observations of a yellow warbler per month summed for some years. Another explanation for the peak could be a more 'showy' behavior of the birds in March.
Yellow warblers spend their wintertime mostly in the red area.
In Colombia and Venezuela yellow warblers can be found all the year breeding in the mangrove along the coast.