Invasion of Yellow-Rumped Warblers

Hoping that my second e-Bird checklist for South Platte Park would significantly exceed my first (see A Disappointing Survey), I headed down to the floodplain refuge on this cool, sunny morning.  Taking my usual 2-mile loop hike, I encountered 30 species, a modest improvement from last month; however, the count included two ospreys, a flock of Franklin's gulls, a tardy group of female buffleheads, a lone loggerhead shrike and a flock of 17 barn swallows, perched in a small tree and presumably exhausted from their migration.

But the highlight of this visit was a tremendous number of yellow-rumped warblers (I estimated 300), foraging in almost every tree that graces the southern section of the refuge.  Indeed, their numbers were so great that the movement of these small insectivores distracted me from other species that I attempted to locate.  Per records provided on e-Bird, this count is more than double the previous maximum for any site in Colorado this year but it doesn't come close to the U.S. e-Bird record of 63,600+ observed at Cape May, New Jersey in the autumn of 2010.

After wintering across most of the central and southern latitudes of the U.S. and Mexico, yellow-rumped warblers return to breeding areas in the western mountains of North America and across Alaska, Canada and northernmost regions of the Lower 48.  During their spring and fall migrations, they often travel in large flocks, a fact that was certainly confirmed at South Platte Park this morning.