Sunday, October 12, 2008

Picking up steam

The milder weather that has settled over the Northeast since mid-week hasn't been great for owl migration, but we're continuing to get one or two birds a night, mostly at our Hidden Valley station. (Small Valley was closed over the weekend while Girl Scouts were using the camp.)

Tonight all three sites will be running, as our third station, King's Gap in Cumberland County, starts up. Unfortunately, the mild southwesterly flow is going to continue for a couple more days, and the moon is rapidly waxing as well -- conditions that are less than ideal for fall migration, when we prefer to see a blustery cold front followed by nights of calm, cold and moonless skies.

But we're continuing to follow "Dizzy," the second-year female saw-whet we radio-tagged on Monday. Yesterday (Saturday, Oct. 11), I spent the day with research tech Anna Fasoli, looking for Dizzy in the Haldeman Tract of Weiser State Forest in northern Dauphin County.

When we met at Small Valley there was no whisper of a beep from the owl's radio transmitter, so we split up and each looped north along different routes into state forest, covering an area about six miles by three miles before reconnecting, driving slowly while listening through the white-noise static on our radio receivers and roof-mounted antennas for any hint of the signal.

Still nothing, so Anna suggested we drive out Wolf Pond Road, which dead-ends after about two miles at a steep escarpment where hang-gliders have a take-off ramp; it's a great overlook, she said, and might be a good spot to pick up a distant signal. But before we reached the hang-glider site, we both picked up Dizzy's signal, booming through the receivers -- she was holed up in a grove of white and pitch pines less than a hundred yards from the road.

Narrowing the search down to a yard-sized area was pretty easy; actually getting a look at Dizzy was not, and we spent nearly an hour shuffling back and forth, alternately waving our hand-held antennas and scanning the dense treetops with binoculars. The white pines were about 75 feet tall and very thick, and we could find no whitewash or pellets. And at that range, the signal was so loud it was hard to localize, even with the gain turned way down, so we tried an old telemetry trick -- jumping off frequency. Instead of setting the receiver to the correct frequency (say, .2850 MHz), we set it to .2950; this attenuates the signal considerably and allows one to take a more precise location. That got us down to one of two neighboring trees, so we jumped another hundred megahertz off the frequency, muting the signal so much that we could determine exactly which pine she was in.

And there she was -- by peering just so through a gap in the foliage, we could see her sitting about ten feet from the top of the tree, holding a deer mouse, on which she was actively feeding. Then it was merely a case of taking all the habitat data that we collect on both the roost site and a randomly selected site 20 meters away.

It's always a thrill to see one of our birds in the daytime, and Dizzy's been a good sport. Our hope is that when King's Gap opens, though, we'll be able to quickly tag an owl there, and shift the telemetry to our normal stomping grounds in Michaux State Forest, where access is a lot easier than we've experienced in the Weiser forest.

Here's a Google Earth image showing Dizzy's movements during the week; the Oct. 8 roost site is based on triangulation, and the colored block shows the rough area in which it may have been. (Lest anyone think we're jeopardizing her by giving out her location this way, consider how long it took us to find her with two radio receivers!)

Scott Weidensaul

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