N.H. Audubon’s annual winter bird survey tracks diversity, and you can help.

If you can tell the difference between a blue jay and a cardinal, New Hampshire Audubon could use your help with its annual Backyard Winter Bird Survey, to be conducted on Saturday and Sunday, Feb. 11 and 12.

This year’s bird count will contribute to more than 20 years of data, which biologist use to find patterns in population changes, said survey coordinator Becky Suomala. She said some species have natural fluctuations while others have steadily gone up or down in numbers.

Sightings of eastern bluebirds and robins have increased dramatically in the survey, she said. This may be because they eat fruit in the winter and the weather has been milder, or because people are growing more fruit, or a combination.

Suomala said the population increases are neither good nor bad, just an indication that birds are responding to changing conditions.

When officials began conducting the survey two decades ago, it showed growing numbers of northern cardinals and mourning doves that had moved up from locations farther south, she said. They were never seen in New Hampshire years ago, but now they are common.

The statewide survey started specifically to monitor the northern cardinal and tufted titmouse, both southern species that were noticed frequently at feeders. More recently, Suomala said, the Carolina wren and red-bellied woodpecker have been moving up.

Two other species showing long-term increases, the wild turkey and pileated woodpecker, set record highs in 2011.

The barred owl was also reported in high numbers last year, she said, possibly because there was a lot of snow cover, making it harder for them to hunt and more likely to visit backyard feeders and scoop up the mice and voles that eat seeds from the ground. She said people might report fewer owls this year, since it hasn’t been snowy.

Last year’s survey also showed large numbers of the common redpoll and pine siskin, which appear to come south in large numbers every other year. The American goldfinch is expected to be in abundance this year.

The house finch, a species native to the western United States, increased dramatically after its introduction to the east in the 1940s, Suomala said. But the survey saw their numbers decline in the early ’90s due to a conjunctivitis disease to which they were particularly susceptible.

The most common birds reported are the ones typically seen at feeders, such as black-capped chickadees, blue jays, dark-eyed juncos, tufted titmice and downy woodpeckers.

Last year, the survey also turned up reports of a pine warbler and a field sparrow, which are rare in winter, Suomala said.

“We always get a few rare birds each year,” she said.

On average, about 75 species are reported in the survey every year. Last year’s variety tied the record high of 77, previously set in 2001.

Some birds, such as sparrows, are hard to tell apart, while others are easy to identify, Suomala said.

“Anyone can participate, even if they can only identify one bird. We just ask that they report only the ones they know,” she said. “If you only know blue jays and cardinals, you can partake and report two species.”

The survey is done in winter to look at populations of birds that are here year round or visit only during the winter, she said. Most of these birds tend to come to feeders in the winter, which makes them easier to count at that time.

Data from the Backyard Winter Bird Survey is used to track changes in both the distribution and abundance of many species. Suomala said reports of a lack of birds are just as valuable as reports of an abundance, so biologists can monitor declines.

She said bird watching is fun and easy, and the survey can be done in a short amount of time.

“Sometimes the best place to start is in your own backyard,” she said.

Each year about 1,300 residents participate in the Backyard Winter Bird Survey by counting the birds in their own backyard during the designated weekend and sending the results on a form to New Hampshire Audubon.

To receive a copy of the reporting form and instructions, send a self-addressed, stamped, long envelope to: New Hampshire Audubon, Winter Bird Survey, 84 Silk Farm Road, Concord, NH 03301. Forms are also available at www.nhaudubon.org. Results from past years also can be found on the website.

Also in February is the Great Backyard Bird Count, a nation-wide, Web-based survey held from Friday to Monday, Feb. 17 to 20. Visit www.birdcount.org.