For over an hour or two I watched and photographed this adult Yellow-rumped Warbler (Dendroica coronata) running itself ragged collecting insects, mostly mayflies. I presumed it was bringing them back to its chicks.

Then I eventually saw the chicks and realized this warbler was running itself ragged feeding not warbler chicks, but the chicks of a Brown-headed cowbird who had deliberately and secretly laid her eggs in the warblers nest and then left them for the warbler to raise.

The warbler parents somehow don't recognize that they are not raising their own chicks, but insatiable parasitic birds. To make it even worse, I eventually noticed that there were not 2 cowbird chicks this warbler was trying to feed but a third one hung just a bit farther back. Three insatiable mouths!

When the time came for me to head back to my campsite, I notice a female adult cowbird casually feeding at her leisure in a grassy area not 50' away. Kinda made me mad.

Location: Swiftcurrent Lake, Glacier National Park, MT