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

Tuesday, October 25, 2011

Fifteen years, and counting

They say time flies when you're having fun, and that certainly true for the Ned Smith Center's owl research program. It's difficult for me to believe that this marks our 15th year of studying the ecology and migration of northern saw-whet owls.

The NSCNA project was one of several that began in the fall of 1997 with modest assistance from the Pennsylvania Wild Resource Conservation Fund, whose symbol is the saw-whet. The WRCF allocated about $9,000 to buy enough nets, audiolures and banding equipment to set up nine owl-banding sites across the state, all operated by volunteer banders.

The center's first site was at a private cabin along Mahantongo Mountain in northern Dauphin County, and that year the crew was thrilled to catch 24 owls. The next year we'd moved our operations to the top of Berry Mountain, and the catch jumped to 73 – we thought we'd figured it all out.

The following year, 1999, we began running three fulltime stations – Berry Mountain, one on South Mountain in Cumberland County, and one along Second Mountain in Schuylkill County. That year also marked one of the periodic irruptions that bring huge numbers of saw-whets south, and we banded 727 owls – almost 10 times what we'd caught at Berry Mountain the year before.

Since then, we've banded nearly 6,000 owls – as well as conducting nearly a decade of intensive radio-telemetry work to study their roost sites and nocturnal habits; collaborative studies with researchers looking at the spread of avian influenza, West Nile virus and tick-borne pathogens; deployment of high-tech geolocators to try (thus far with limited success) to study long-term owl movements; and much more.

The only thing making that possible is the incredible commitment of our crew of volunteer banders and assistants – 18 federally licensed banders and 85 assistants, who in total give between 5,000 and 6,000 person-hours a year to this project.

We opened our sites Oct. 3 for this, our 15th season, with as much enthusiasm as we had all those years ago. It's been a slow start, though, in part because of the warm and wet weather with persistent southerly winds, and in part because we've been expecting this to be a slow year, a low point in the saw-whet's population cycle.

How slow? At this point last year – which was just a little above average – we'd caught 146 saw-whets. This year, all three of our sites together have netted just 10, six of them in the past three nights.

I was sharing this news with a group of visitors the other night, and someone raised their hand and asked, "Aren't you alarmed that the owls are declining so badly?" No; this is normal for saw-whet owls, a species that undergoes huge and predictable fluctuations from year to year.

Like many northern raptors, their fortunes are tied to the abundance of their prey (small rodents), most of which have roughly four-year population cycles themselves. When the voles and mice are common, the owls produce a bumper crop of babies – and we have a flight like the one in 2007, when we netted almost 900 owls.

When the rodent cycle bottoms out, as it did this year, the owls produce few chicks, and we get a year like 2006, when we caught barely 200 saw-whets. This fall is shaping up to be one of those years.

The good news is that the mouse cycle is on the way up again, and next year ought to be one of those periodic irruptions, when the skies are filled with migrant owls. And whether it's a good flight ot a meager one, each new season helps us better understand what's driving owl migration – which is why we spend our nights in the woods.

Scott Weidensaul

Research director, Ned Smith Center for Nature and Art