Invasion of the Butter Butts

Photo by John Harrison

Yellow-rumped warblers (Dendroica coronata) have invaded Minneapolis!  In the last couple of days, they have been everywhere!  Yellow rumps (affectionately known as Butter Butts) are one of the first warblers to arrive in the spring, and they are sure proving it this year.

Over the last few days, it has been a joy to watch the Butter Butts in our neighborhood.  It is really cool to see warblers after their long absence.  And they are highly active, colorful feeders that are fun to watch.  We've had them in abundance all around our condo - they are in the trees, in the bushes, on the sidewalk, in the alley, on the neighbor's roof, in the lawn - everywhere!  We grilled out in our backyard tonight, and the Butter Butts were not scared away, and in fact they were often just feet away from us, despite the fact that we were doing nothing to be quiet or unobtrusive!

One of the adaptations that makes it possible for Yellow-rumps to arrive earlier than other warblers is their ability to digest waxes.  These little birds can digest waxy berries, such as those of the wax myrtles and bayberries, that other birds are incapable of digesting.  Having an alternate food source is highly convenient when you are trying to race north.  For most insect eating species, it can be disastrous when a cold snap comes during their northward migration.  As we know all too well from this spring in Minnesota - cold weather and snow can come along much later than normal average dates.

If such cold snaps cut off food supply, even a few days of colder than average weather could be fatal.  However, the Yellow-Rumps (along with Tree Swallows) have developed the ability to digest waxy berries.  If a cold snap comes along and cuts off the supply of insect food, they switch over to the few waxy and unpalatable berries that have stayed on the bush over the winter.  This extra food supply is often enough to get them through a few days of unseasonably cold weather.

Welcome back, Butter Butts!