Christmas counters find fewer birds going south

They are rare birds, these amateur ornithologists. Their activity is part walk in the woods, part collection, part academic study, and a large part an appreciation of beauty.

"I saw an owl when I was 10," said Tom Young, 38, who grew up in Essex and coordinates the Newburyport portion of the annual Christmas Bird Count, which concludes Sunday. Like many others birders, he said, he can recall the "crystallizing moment" that drew him to a lifelong hobby.

This year, local birders have seen a new trend in the data that has led to some unsettling conclusions. It is a common discussion in birding circles about the correlation between a changing bird population in Massachusetts and the disturbing ecological trend known as global warming.

As the earth has warmed over the past few decades, according to most climatologists, birders are finding fewer migratory species from the northernmost regions, and more and more species of birds that -- 30 years ago -- would never venture this far north in December.

"Global warming is one of these things that, in many minds, is still somewhat controversial," said Wayne Petersen, co-author of "Birds of Massachusetts" and director of the Massachusetts Important Bird Areas program for the Massachusetts Audubon Society. He's also the longtime regional editor for the Christmas Bird Count in New England, compiling the figures sent in from local counts.

"Having said that, and the fact that it increasingly seems there is overwhelming evidence to suggest it's real, the Christmas Bird Count is one way to get a hint of that."

The best example, he said, is the trend of more and more species of birds -- many of which are highly migratory -- showing up on the Christmas bird count.

"The implication is that they're staying later, or not migrating as early in the fall, or wintering farther north then they ever did," said Petersen, who offered as an example the sighting of three hummingbirds recorded in the first few days of the count this year.

"That's unprecedented," he said.

Warblers are another species being seen in greater numbers. That's a species that frequently winters in the tropics, but is showing up on the Christmas Bird Count.

"There have been a variety of other species of this sort, that if you go over the last five or 10 years or so there's an increasing trend of a lot of these species appearing in December that were never here before" at that time of year, Petersen said. "They're usually gone by October or November at the latest."

In 2002, Ivan Valiela, a professor at the Boston University Marine Program in Woods Hole, coauthored (with student Jennifer Bowen ) an academic paper that tracked the trends from Christmas bird counts and matched them with recorded temperatures.

"What has been happening in the last few decades is that there's a higher and higher proportion of species that, in previous decades, used to be fairly south in the winter and now manage to survive -- do well, even -- in our winters, at this latitude," he said.

In constructing the study, Valiela and Bowen reviewed Christmas bird counts in Massachusetts, which run back to the early 1930s.

"It's really quite a remarkable data set, of places where excellent bird identifiers have had the chance to collect information in the same areas, in basically the same fashion, for decades," he said. "We can also collect data on the temperatures, and what seems to be happening is that as there's this gradual warming, there's also a gradual movement of species northward.

"You can go species by species and see the pattern," Valiela said. "Gradually, these species with southern affinities have been moving northward." And species with northern affinities are moving farther northward.

On Tuesday, approximately 35 volunteers were to fan out in a 15-mile circle, observing birds and gathering data, for the Newburyport bird count. Last week, many of the same volunteers participated in similar counts on Cape Ann and in the Andover-Boxford area.

The participants look forward to their day (or days) taking part in the bird count for a variety of reasons. Some like to go out in teams, Young noted, and most are fueled by the possibility of an unusual find that they can share with appreciative birders at the end of the day.

"It gives you an excuse to be out all day long, and every bird counts because every bird needs to be counted that day," said Jim Berry of Ipswich, 63, who participated in both the Cape Ann and Newburyport counts.

Berry explained that common birds are frequently not given much attention during normal birding.

But because he's collecting comprehensive data, "you have to pay more attention, and need to be more intense," he said.

The Christmas Bird Count, a citizen-scientist project sponsored by the National Audubon Society Inc., dates back 107 years.