Werts and Carraway?
Does this come from your Teutonic heritage? In German, Werts would be
pronounced Verts, but he actually spelled it that way,
Wayne
From: "Lars Per Norgren" <larspernorgren@xxxxxxxxx>
To: "obol" <obol@xxxxxxxxxxxxx>
Sent: Monday, March 21, 2016 10:44:15 PM
Subject: [obol] winter Butéos and voles
There are two species of voles in the Willamette Valley. Microtus canicaudis is
prone to wild fluctuations in numbers, sometimes more than one per square foot.
Under these circumstances hawks can hunt without flying. There was white clover
field southwest of McMinnville a few years back that attracted many birders due
to the presence of a Ferruginous Hawk. There the raptors were often walking,
not running, from mouse to mouse. According to Werts and Carraway (Land Mammals
of Oregon) M. townsendi has much more stable populations.
Rough-legged hawks are arctic nesters, prone to population swings similar to
Snowy Owls. There must have been plenty of food up north last summer as I saw
more Rough-legs this fall and winter than any previous season I can remember.
Weather to our north must be involved as well. Extensive snow would force some
ground feeding hawks further south than they would otherwise travel. Resident
Red=tails are greatly augmented by migrants from various points to our north.
They too surely have variable breeding success from year to year. We tend to
put a lot of emphasis on phenomena we can observe directly.
Lars
