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