Photo credit: Dan Lory

If you see a tiny 5" long bird crawling its way headfirst down a tree trunk, chances are it's a nuthatch of some kind--probably a White-breasted Nuthatch, if you're in the Chicago area. They move ceaselessly in slow spirals around the trunk, looking for insects and making little nasal grunt-like noises until they reach the bottom of the tree. Then they fly up and start over. Except for one type of warbler, no other bird besides the nuthatch has this tail-up hunting method. 

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And there's not much tail to speak of. Did the nuthatch develop its hunting method because its tail is too short to support a head-up posture (like woodpeckers)? Or did its tail gradually diminish in size because its head-down posture makes a long tail unnecessary? Maybe Darwin knows. But who cares. They're such fun birds to watch. 

Hard to get them to sit still for a photo, though.

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Dan's Feathursday Feature is a weekly contribution to the COS blog featuring the thoughts, insights and pictures of Chicago birder, Dan Lory on birds of the Chicago region.