Wednesday, October 29, 2008


The huge nor'easter that came roaring through eastern Pennsylvania Tuesday wiped out our banding, since rain, snow and 40-50 mph winds are not conducive to catching owls. Some of the higher ridgetops just north of us got walloped with 15 inches or more of snow.

Besides canceling banding, we'd planned a major night of triangulation tracking, with three teams of trackers and helpers -- all to naught. It was a good night to curl up in front of a fire.

However, despite the rain (and lots of fallen trees and falling branches), research tech Anna Fasoli was out during the day checking on our three radio-tagged owls. She found them all more or less where they'd been the day before, having moved anywhere from 70 to 231 meters.

Here's a sneak peek, though, at what we're working so hard to get this fall -- an evening activity map for Autumn, one of the King's Gap owls we've been tracking, at a previous roost she's long since left. This was from a tracking session from dark until about midnight on Oct. 19 -- the yellow dot shows Autumn's daytime roost, and the yellow X's mark the spots where Anna and research intern Drew Weber were standing, taking bearings on the radio signal from Autumn's transmitter.

The red dots are where the bearing lines intersected, giving the owl's position (the numbers are time markers - 2310 is 11:10 p.m. EST). We usually take bearings about every 10 minutes, and we try to position ourselves so the bearings intersect at roughly 90 degrees, which gives he most accurate position -- but as the owl moves that isn't always possible, and sometimes Drew and Anna were taking bearings almost directly toward each other. Those inaccurate readings aren't included on the map, which is why there are some gaps in the time line.

Still, this gives us a pretty detailed picture of her movements over the course of almost five hours, moving around the oak/black gum/pine forest on King's Gap's southeastern border. There have only been a handful of attempts to get this kind of activity data on saw-whets before -- once in the 1960s in Minnesota, using an automated system to monitor a single saw-whet in a large woodlot, and again with two breeding males in Idaho some years later. Those studies found that the saw-whets were using areas ranging from 115 hectares (about 284 acres) to 159 hectares, but also that one male's core range was only about 27 ha. (about 66 acres).

In rough terms, Autumn's activity area was about 32 hectares, or about 80 acres. This was not her full night's activity range, but probably represents her first main hunting bout, moving around looking for a mouse, then settling down to eat it. But it begins to shed some light on how large an area these birds need to hunt, and what kinds of habitat and terrain they use in doing so.

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