Friday, November 4, 2011

Watching the nets...and the radar

I can't say it's never been this slow, but only one season out of the past 15 years – 2006 – has been quite as dreary as the current one.

As of Nov. 3 our total is just 54 saw-whets. Compare that to the 302 we had on this date last year, and you'll understand why it's been a painfully slow season for us. Yet our crew seems to maintain their enthusiasm without a problem, which I find remarkable. They're an amazing group.

The weather did us no favors last weekend, either. The freak October snowstorm that pasted the Northeast left anywhere from 10-14 inches of heavy, wet snow at our three banding stations, bringing down trees and huge limbs.

None of the nets were damaged, but King's Gap State Park, site of our westernmost station, was without power until Wednesday night, and some of our crew members in southcentral Pennsylvania are still in the dark.

We're finally back in full operation, but the pace remains slow in what should be our busiest week of the migration. Once the snowstorm cleared, the flights did pick up a bit. We caught a total of three saw-whets on Oct. 30, the night after the storm, followed by nine on Halloween, 11 (our best night this year) on Nov. 1, five on the 2nd and seven last night, Nov. 3.

But while the banding has been slow, we've also doing some interesting experiments in advance of a big study next year into the dynamics of saw-whet migration. This week I've been working with Tom Magarion of New Jersey Audubon to use radar to monitor nocturnal bird migration along the Kittatinny Ridge, about eight miles southeast of our Hidden Valley site.

Working out of a U-Haul-sized trailer, we've been using both the roof-mounted horizontal (surveillance) radar and a side-mounted vertical-beam radar to watch the movements of nighttime bird migration along and across the ridge. The surveillance radar is the kind you're probably thinking of, which shows a huge circular field a mile or two in diameter, with blips moving across it. The vertical beam sweeps a narrow swath of the sky from horizon to horizon, giving us good data on altitude.

The results have been fascinating. Wednesday night there was a modest 3-8 mph southwest wind, and the birds were flying fairly low – and almost all of them were traveling due north, for reasons neither Tom nor I could explain.

Last night was almost dead calm and about 8 degrees C, with an approaching weak frontal system that brought clouds about 10 p.m. This time there was a big lift-off of mostly songbirds just after sunset, and throughout the night the vertical radar showed a heavy flight that was most quite high – from 3,000 to 6,000 feet up.

We were also running a few nets and an audiolure, and on several occasions with a night-vision video link we observed saw-whets bombing down into the nets.

Finding a good location for the radar, which combined the right topography on a ridgetop, a sufficiently large clearing and decent access, was quite a process. Both the PA Game Commission and PA Bureau of Forestry were incredibly helpful, and while we're indebted to PGC land management officer Matt Belding for permission to work on SGL 110, I'm also grateful to DCNR research forester Chad Voorhees for getting us permission to test a site on Weiser State Forest.

Scott Weidensaul


Owlman said...

Hi Scott any updates on your project? I heard a fellow owl enthuasist mention that some people think that Saw whet may be the most common North American raptor. Have you heard that before? I would love to see a post on finding Saw whet based on the habitat, roost preferences etc.

Scott Weidensaul said...

We're wrapping up our work in a day or two, so I'll have a final post shortly on the season, which has been a record-setter in ways we'd rather not have.

As for using habitat preferences to find saw-whets, the more we study them, the more I'm convinced there's no such thing as "typical saw-whet" habitat - they seem more focused on structure than species composition. As long as there is dense understory and - in winter - some evergreen component (conifers, rhododendron, laurel, wax myrtle, honeysuckle, etc.) they're happy.