Friday, November 27, 2015

Northern Harrier

John Holden drove near Circle Lake in Rice County, Minnesota, on Wednesday. I spied an odd raptor perched near the ground along the roadside. We made a quick U-turn and stopped on the wrong side of the road. The hawk’s strange face and long legs both suggested a Northern Harrier, but its small size and brown coloration left me a bit perplexed. This hawk turns out to be an immature harrier as indicuated by its unstreaked, buffy underparts and by the large amount of white on the head. The small size suggests that it is a male.
Unlike most other hawks, harriers have facial disks—indicated by the white stripes around the head. This disk works like a parabolic reflector. Harriers consume a wide range of prey—small to medium-sized mammals and birds. The facial disk is an aid because the birds rely on auditory and visual cues to find their prey. Harrier numbers are dependant on vole poplulations. When there are few voles, harrier numbers crash. When voles are abundant, harriers rebound. Indeed, in times of plenty, male harriers take on multiple mates (Smith et al. 2011).
As we watched, this harrier lifted its tail and wings and shat. I considered deleting this last photo, but bird excrement is interesting. (Also of note is how much of the bird’s body consists only of wings and tail—as you can see by the source of the excrement, the bird’s anus is located well toward the center of the raptor’s total length.) Take a careful look the next time you see a bird dropping. The urine is a pasty, white substance that is composed of uric acid (not urea like in mammals). The excrement consists of small, black specks within the paste.

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