At the Point Reyes Bird Observatory near Bolinas, staff members venture through the woods on a trail they have followed since 1966. What they're after are wild birds that fly into gentle nets that capture and immobilize them just long enough for researchers to examine them.
It's part of a long-term study, tracking the changes in the age, weight size and general conditions of a species. When Rae Goodman crunched all of the data for her master's thesis at San Francisco State, her results puzzled everyone.
"These are small changes," said Nat Seavy, Ph.D., "but statistically significant."
The significance of the discovery is that scientists were pretty much convinced that as temperatures warm, species got smaller. That's been the idea since 1847, but now they're finding that birds are getting bigger by as much as 10 percent, and they don't know why.
"It's just a couple of grams," said Goodman, "but these are small animals. If a 200 pound person gained 10 percent, that would be 20 pounds, a big difference. The person would notice it."
One theory as to why the species are getting larger: Warming temperatures may be increasing the amount of food. Another theory: The smaller birds are dying off because they can't compete.
Strangely, some birds are getting larger while their numbers are declining.
"What is interesting is it's not just a particular bird, but an entire range of birds that are migratory and resident," said Goodman.
As to what this means, there are no clear answers. That's what long-term studies are for.
But when nature adapts to whatever is causing these changes, at least we will have a long-term database to study, and Rae Goodman -- who teaches high school science now -- can say she has made a significant contribution.