Warblers bring flashes of color to spring and fall foliage, and while several species breed here in summer, most stop only briefly in New Jersey during migration between breeding and wintering grounds; as many as thirty species can be seen there during the fall migration. Warblers over-winter in the tropics, then in spring travel northward along rivers, coastlines, and mountain ranges, aided by the sun and stars, with most that pass through New Jersey breeding in Canada and the northern United States, where they nest and raise their young before returning to the tropics ahead of cool autumn temperatures. Declines in songbird populations, including warblers, have been observed across much of their range, and recent research suggests links to habitat loss in tropical wintering forests, fragmentation of northern breeding forests, and the continuing loss of coastal forests used as resting places during migration.