Videos let scientist get up close and personal

Posted: Sunday, July 15, 2001

During a two-year period, Steve Lewis watched goshawks for 5,800 hours, about 341 days of viewing.

Much of that viewing was on tape, however. As a graduate student at Boise State University in Idaho, Lewis performed an in-depth study of goshawk feeding behavior during the birds' breeding season for his master's thesis project during 1998 and 1999.

"Goshawks are pretty cool birds," Lewis said. "I learned a lot of lessons, depending on how close the camera was and depending on how the sun was."

Lewis set up video cameras at 10 nests, enclosing the 2- to 3-centimeter devices in waterproof boxes to protect them from the weather. The boxes were bolted directly to the nesting tree, with a cable running to a VCR, television and battery pack on the ground.

"It was just sort of like a surveillance camera you'd see in a 7-Eleven," Lewis said. "I would have someone (on the ground) helping me. I'd be moving the camera around and they'd look down at the image on the TV until I got it to the right spot. Then I'd just fix it to the tree and I'd climb down."

The VCRs were programmed to come on 15 minutes before dawn, then shut off 15 minutes after sunset. On the average, they ran for 19 hours a day and delivered an unparalleled wealth of information, Lewis said.

"Another good way to do this is to sit in the blind and look," Lewis said. "But you couldn't even come close to that sort of time. There's no way you can sit here and pay attention for this much time."

Four of the cameras were set up around Juneau. Others were placed on Prince of Wales Island west of Ketchikan. Lewis had roughly 42 days of observation time from when the young birds hatched to the day they left the nest. He recorded more than 1,600 feedings, but it was necessary to watch the tapes repeatedly to determine just what the goshawks were eating.

"It was time consuming," Lewis said. "I ended up going through them twice."

While some of the prey - such as a brightly colored Stellar's jay - were easy to identify, the majority had few distinguishing characteristics. Many were identified by their feet, with varying degrees of accuracy. Lewis said he could determine the genus of the prey roughly 79 percent of the time.

His results showed that Alaska's goshawks follow the same general eating habits as those in the continental United States and Canada, with birds in the Juneau area eating mainly blue grouse and red squirrels.

"That's sort of classic fare for goshawks," Lewis said.

The birds on Prince of Wales Island had a harder time finding food, as blue grouse and red squirrels do not live there.

"We don't have really great evidence," Lewis said. "But there's not a lot of goshawks down there, and probably one factor is these two big items - they're not down there either."

In one of the nests Lewis observed on the island, eggs hatched but no birds were fledged. The young killed one another, likely because of hunger.

"The young attacking each other doesn't occur when there's plenty of food," Lewis said.



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