© USF&WS
Here's a fascinating account of foraging behavior observed by myself and several other birders yesterday that I thought you might enjoy:
A Black-throated Blue Warbler was foraging in thin twigs protruding from the side of a tree about 10 feet from the ground. We were about 20 to 25 feet away so we had great viewing in good light. We became somewhat alarmed when it appeared the warbler was stuck on a twig. Then it began to bounce on the twig...at first without beating its wings but sometimes fluttering a little with its bill raised upward. In all sincereness, it looked like it was exercising on a trampoline. Upon closer observation the warbler was using the bouncing motion to systemically disconnect an orb spider web from the surrounding twigs. Once the web was disconnected, it reeled it in with its bill and then consumed the enswathed insects from the spider's cache.
From Cornell's BNA online (Black-throated Blue Warbler):
The most frequent prey capture method is to snatch prey from a substrate, usually a leaf, while hovering or flying past (65%); secondly (35%), they glean prey from nearby substrates while standing on the vegetation (Robinson and Holmes 1984). Unlike other species in northern hardwoods forests, they do not change their relative use of foraging maneuvers or search tactics among tree species or strata, suggesting more stereotyped foraging behavior (Robinson and Holmes 1984). In laboratory experiments, however, their foraging behavior changes with leaf shape and position in relation to available perches (Whelan 1989b, 2001), suggesting that plant morphology influences their foraging success.
Warbler activity at Pheasant Branch Conservancy yesterday was fantastic - 17 warbler species!