Studies have shown that birding and related activities outdoors are providing billions of dollars to the nation's annual economy, and experts say it's a trend that is growing around the country.

Many people who like to go birding buy equipment, travel and book hotel rooms and rent cars, and eat at local restaurants - among other activities.

Mark Hart works for the Arizona Game and Fish Department, which is traditionally associated with hunting and fishing but is seeing a growing interest in "Watchable Wildlife" programs.

"Birders are an interesting group," Hart says. "They tend to either have discretionary income or be retirees who can't go, say, mountain climbing but want to get out into nature, and so they go birding and they spend money where they go."

Hart says Southern Arizona offers plenty of year-round opportunities for these activities, including sandhill cranes in the winter and hummingbirds in the summer.