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

Wednesday, November 18, 2009

Was it something we said?

After having several terrifically cooperative owls like Isra, which we were able to track for more than three weeks, we've had a run of bad luck on the telemetry front. Fang and Feist, which we radio-tagged last week, both departed over the weekend while Drew, Kim and Hannah were enjoying a couple of days off.

So Monday night they tagged the only owl the King's Gap banding crew caught, a hatching-year female. They bandied around a couple of delicious food-themed names but thought better of it. "We were going to name it Meatballs, but we decided saying that name all night might make us hungry." Drew told me when he called from the woods around 9 p.m. with the news. "We figured it wouldn't be as big a problem with an owl named Tofu," so that's what they went with.

Instead, Tofu posed other problems. After tracking her for several hours near the banding station, the telemetry team followed her as she moved south over the ridge to Cold Spring Hollow, checking on her position every 10 minutes. And then around 3 a.m., between position checks, she simply disappeared. The crew fanned out for the rest of the night, checking from high points throughout Michaux State Forest, but Tofu had left the buffet.

Last night they tried for another telemetry owl at King's Gap, but came up dry - while we had owls at the other two sites, there were none caught at KG. We'll try again tonight.

We're up to 358 saw-whets and five screech owls for the season, still getting two or three a night at each station. In the past week we've had a number of foreign birds come into our nets ("foreign" meaning banded at another site), while several of our owls have shown up elsewhere.

Among the owls we've caught were birds banded at Tadoussac, Quebec in 2007; several from Glenn Proudfoot's operation at the Mohonk Preserve in southeastern New York; and three from Virginia - an owl banded in 2004 in the highlands of western Virginia, one banded in February 2008 in Shenandoah River State Park, and one banded in November 2007 at Kiptopeke on the southern tip of the Delmarva Peninsula. We've caught several other owls for which there was no data in the Banding Lab database.

Our owls have shown up in the past week in South Hadley, Massachusetts; Elk Neck State Park in northern Maryland; and several at Lamb's Knoll in the Catoctin Mountains of western Maryland.

We've also - finally - reached the end of the line with our geolocator project. Last night, Guy Ubaghs deployed the last two at Small Valley - 178 of the tiny tracking devices, which are continuously recording data that will allow us to determine the owls' daily latitude and longitude once we start recovering some of them next year.

None of this would have been possible without an extraordinary effort on the part of our banding crew, especially the banders from Small Valley, who double-teamed most nights this fall so one person could band and the other deploy up to 10 geolocators per night.

A few geolocator-tagged owls have shown up in our nets, and Sunday night I got a call from Dave Darney, who bands saw-whets on the Allegheny Front in Somerset County. He'd just caught a geo-tagged owl we released Nov. 6 at our Small Valley site, about 110 miles to the east. After checking the owl (it and its harness were both in fine shape), he released it - we're hoping to get up to two full migration cycles from the geolocators, so there was no point in taking it off after just nine nights and a relatively short distance traveled.

Monday, November 16, 2009


Here is a a picture of Fiest, being held by Alex L. before being released. We were tracking our other owl, Fang, but kept checking up on Feist to make sure she was around. In the morning we found her roosting high up in a white pine. We have been spoiled with the owls choosing pitch pines to perch in where they are often easier to see. White pines have denser needles and limbs, so a saw-whet that is perched high is hard to spot.

Friday, November 13, 2009

Busy week

We're supposed to be on the downward slide to the end of the owl season, but it doesn't feel like it.

Normally, our peak flights come right around Halloween, but a full moon Nov. 2, and a lot of unseasonably mild air, seems to have delayed the migration. The couple of big nights we had on Oct. 18 and 25 tend to mask the trend, but if you look at our capture totals in seven-night blocks, here's what you find:

Oct. 1-7: 0 saw-whets
Oct. 8-14: 9
Oct. 15-21: 74
Oct. 22-28: 60
Oct. 29-Nov. 4: 63
Nov. 5-11: 98

Last night, the 12th, we had another 21 owls between the three sites, and reports from the north make me suspect there are more to come. Holiday Beach in Ontario, across the river from Detroit, is still getting 20-30 owls a night, and Prince Edward Point, on the northeast shore of Lake Ontario, banded 500+ owls this season, of which only two have been recaptured - we normally get a lot of PEPtBO's birds, suggesting they're still to our north.

We've had a bunch of interesting foreign recaptures this week as well. Two have come from Glenn Proudfoot's operation at the Mohonk Preserve in southeastern New York, one from Quebec in 2007, and another from Virginia in 2008. We also caught another old saw-whet, banded as a hatching-year (juvenile) in 2004 by Clair Mellinger in Bergton, VA - which was quite a coincidence, because in 2005 we caught another of Clair's owls, banded that same night the year before.

So far we've caught 22 foreign owls, while eight of our birds have been reported from other sites. Both totals are a little on the low side, especially the latter.

The telemetry crew has been busy all week. Esmeralda had been hanging out south of King's Gap on private land, so they focused their attention on Isra, who has been a real challenge to track, covering a much larger area than past owls have done this year or last. Here's an example of one partial night's tracking, from dusk at 18:00 hours until about 2 a.m.; the polygons are color-coded from pale to dark to make it easier to follow her movements over time.

The results of one night of tracking Isra, the wandering saw-whet. (©NSCNA)

That night, she covered an area about twice the size of a typical half-night track for one of our 2008 owls. Whether this is just an expression of her personality, her hunting skill (or lack thereof) or a general scarcity of prey, we can't yet say.

On Tuesday night, I joined the tracking crew to follow Isra around Buck Ridge and upper King's Gap Hollow. That night she was behaving herself a little more, making it easier for Hannah and Drew to track her, although Kim had to keep shifting to get a clear bearing.

That same night, the KG banding crew put another radio on a new owl, an adult female nicknamed Fang (hey, just because we think they're cute doesn't mean they aren't ferocious little predators). Two nights later, they tagged an HY female dubbed Feist, because it pulled so much blood from Drew during harnessing.

The timing was perfect, since both Esmeralda and Isra left the same night. Isra in particular had been a real trouper, sticking around since Oct. 19 and giving us a lot of data.

We're almost done deploying our geolocators - out of 178, we have about 15 left. None of the geolocator-tagged owls have turned up at other sites, but then, only one of the 326 owls we've banded so far this year have been recaptured by another site - the remarkable "Wrong Way" Corrigan of an owl I wrote about last weekend.

Sunday, November 8, 2009

Wrong Way Corrigan

Our own Wrong Way Corrigan after her recapture (©Tom LeBlanc)

In 1938, aviator Douglas Corrigan made a transcontinental flight from California to Brooklyn. Flush with his success, he wanted to try another nonstop flight immediately, this time across the Atlantic from New York to Europe. He'd been trying to get permission for the flight for two years, but his rickety plane, which was basically held together with spit and baling twine, was not considered safe, and his flight plan was again denied.

Corrigan took off, supposedly to return home to California. Instead, he landed 28 hours later in Belfast, Ireland, and until his dying day he swore that he'd simply gotten lost. Manhattan threw him a tickertape parade, the New York Post ran a backwards banner headline that read HAIL WRONG WAY CORRIGAN, and a legend (and an expression) was born.

It looks like we have our own Wrong Way Corrigan. On Oct. 26, my crew and I banded 24 saw-whets at our Hidden Valley site in Schuylkill County, just north of the town of Friedensburg. The last owl of the night was an after-second-year female (meaning she was at least three years old, possibly older).

Imagine my surprise when I learned that this same owl was recaptured Friday night - not south of us, as you'd expect, but in Allegany State Park near Salamanca, New York, at a site run by bander Tom LeBlanc.

That's almost 170 miles to the northwest - the wrong way for any bird that's supposed to be migrating south for the winter.

The odd thing is, this isn't all that odd. Coincidentally, the day before this recapture, a number of saw-whet banders had been discussing birds moving in unexpected directions - speculating whether this was a result of immature birds undertaking a form of dispersal flight, or a manifestation of the nomadism many of us suspect is a constant theme in saw-whet life.

The subject arose when banders in Massachusetts twice recaptured (at two different sites) an owl banded in a previous fall in Kentucky. Some of our birds banded in Pennsylvania have subsequently been caught in Illinois, Michigan and Ohio, and we've caught owls banded in Michigan, Wisconsin and western Ontario. But in most of these cases, a year or more elapsed between banding and recapture.

Last year, however, another of our owls (also an adult) made a long flight to the northeast, showing up 118 miles to the northwest a week after we banded her, in nets run by our colleague David Hauber near Hebron, PA.

So what's going on? I tend to think this has less to do with "lost" owls and more to do with an evolutionary approach that uses nomadic behavior to find areas of abundant food, both during breeding and nonbreeding seasons. After all, historians like to point out that whatever his claims to the contrary, Corrigan certainly knew exactly where he was flying.

There is circumstantial evidence to suggest that saw-whets are highly nomadic during the nesting season - that unlike most birds, which return faithfully to the same nesting territory every year, saw-whets may slosh around the boreal forests of Canada and the northern United States - maybe in Quebec one year, and the next in central Ontario, where the mast crop (and thus the rodent population) is higher. Then in the fall, instead of coming south through New York and Pennsylvania, the owl crosses through the Great Lakes region into Michigan and Illinois.

They may also be nomadic in the nonbreeding season, too, shifting widely across the landscape. While rare among raptors, such constant wandering is common among many boreal birds, like crossbills and pine siskins.

This is just speculation, but our geolocator study may shed some light on these questions. Because the data loggers will collect information from which we can plot the rough daily position of the owl for up to two years, we may finally get some hard evidence to explain whether they are as nomadic and unpredictable as these rare banding encounters suggest.

Unfortunately, because I was shorthanded the night we caught this owl, I didn't fit her or most of the other saw-whets that night with geolocators. But I suspect the owls we have fitted with the devices will provide some real surprises when we start recovering some of the geolocators next year.

Thursday, November 5, 2009

Owl Nightlife, or... what does a saw-whet do at night?

We have now been tracking Isra for over 2 weeks now, with a lot of good data coming from our long nights at King's Gap and in the Michaux State Forest. With the migration season in full swing for the owls, we are now starting to hear the strange barks and whines of the saw-whets as we are walking through the forest. Sometimes it's the owl we are tracking, but often it is another saw-whet in the woods.

Isra perched high in a pitch pine

Isra has a routine going for her that she repeats every night we have been tracking her. Soon after dark, she leaves her roost and becomes very active, flying back and forth along the King's Gap/Michaux State Forest border. She keeps us on our toes as we run around, trying to figure out where she is off to. Several times she has completely ditched us, only to show up back at near the banding station at King's Gap.

After flying around for several hours, presumably hunting, she often settles down for several hours and gives us some time to relax and enjoy the night sounds other than our feet crunching the newly fallen leaves.

Isra often stays relatively still until shortly before dawn, when she starts flying again and soon ends up in the pitch pine where she will roost for the day. As the sun comes up, we get to go search for the roost site so we know where to find her the following evening.

Mornings are great at King's Gap because there are steady streams of migrating birds flying around. Currently, American Robins steal the show but grackles and juncos are also common in large flocks.