Yellow-rumped Warblers and poison ivy berries...

Butter Butts and poison ivy berries go hand-in-hand in autumn. If you find a large patch of poison ivy berries high in a tree, keep your eyes open, because sooner or later a Yellow-rumped Warbler will happen by and gobble up the tasty treats...

A fall Yellow-rumped Warbler perches in a tangle of poison ivy in a Sycamore tree. Good eats for the wee bird, a winter food supply of waxy berries entices a few of these warblers to overwinter in our area! 

In autumn and early winter, Yellow-rumped Warblers switch their diet from the abundant insects of spring and summer, to the abundant waxy berries of fall and winter. Because this warbler can survive without insects being its primary diet, it is the only spring warbler to overwinter in Ohio. All the other neotropical migrants head south for the winter where the insects still roam free. Not all of the Yellow-rumps migrating through our area stay all winter, however. Most head south as well, but you can usually see a few in the woods on bird outings all winter long. Rick and I have seen them many times along the Little Miami River in the winter.

The tell-tale camera click gives me away every time!
"Really?" our little warbler seems to say. "Can't you see I'm dining on poison ivy, the most delectable of all the berries? No photos, please." 

Oh, what a tangled web...of poison ivy vines! This very old sycamore was covered in hairy poison ivy vines, and the tree hosted several of the migrating (or overwintering) Yellow-rumped Warblers. 

Of course, Yellow-rumped Warblers are not the only birds to feast on poison ivy berries. Woodpeckers love them too. On winter hikes along the Little Miami River, I've watched Red-bellied Woodpeckers, Downy Woodpeckers, and a Northern Flicker pluck and eat them one berry at a time.

Being able to absorb and metabolize the fat in the waxy coating on the berry is unique among warblers and allows Yellow-rumped Warblers to be the most northerly wintering wood warblers. 

...you can barely see the little "pat of butter" above its tail that gives this sweet warbler its nickname, Butter Butt!

Click here for a previous post that shows a better view of that little pat of butter!

Click here for a look of a Butter-butt in all his springtime glory.

Why can Yellow-rumped Warblers survive on waxy berries in fall and winter?
Almost all the literature on Yellow-rumped Warblers mentions they are hardy warblers that can survive cold winters by eating waxy fruits such as poison ivy berries, bayberries, and wax myrtle, but the literature never explains why, so I did a little searching and found an article that details the warbler's unique digestive abilities in The Auk, 109(2):334-345, 1992 by Allen R. Place and Edmund W. Stiles titled, "Living Off the Wax of the Land: Bayberries and Yellow-rumped Warblers." Click here for the pdf of the article. It explains how Yellow-rumped Warblers are able to efficiently absorb and metabolize the wax that coats many of the fall and winter berries such as bayberry, wax myrtle and poison ivy.