It is a rite almost as familiar as spring: Baby birds, who have tumbled out of the nest or been abandoned. Squirrels injured by predators. Raccoons struck by cars.

They arrive wrapped in blankets or old newspapers, or perhaps cradled in cardboard boxes, brought in by concerned citizens. At Greenwood Wildlife Rehabilitation Sanctuary, they receive the care needed to restore them to health and return them to the wild.

Greenwood cares for 2,500 to 3,000 animals each year, mainly during the warmer months.

"Our busy season is April to October," says executive director JoAnn Windholz.

Staff members have encountered approximately 135 different species of animals. The most common patients are birds and squirrels, although Greenwood has also cared for bunnies, water fowl, raccoons, foxes and the occasional coyote.

One case involved a fox that was badly burned in a fire. Another involved a marmot that had been caught in the wheel well of a vehicle in the Aspen area, and ended up traveling for several miles.

"He got pretty banged up in the process," Windholz says.

When the marmot recovered, Greenwood was required by Department of Wildlife regulations to return the animal to an area within 10 miles of its original habitat, necessitating a bit of a road trip.

Most animals are set free at local release sites that are considered to be safe. Whenever possible, they are returned to the site where they were originally found.

As a licensed rehabilitator, Greenwood follows all DOW regulations regarding the treatment and release of animals. Windholz stresses the importance of bringing injured wildlife to licensed rehabilitators, who have been trained on proper care and feeding techniques.

People who try to care for wildlife on their own often do more harm than good. When feeding birds, it's important to use food that is easily digested, and to ensure that food or water make it past the glottis, otherwise the bird may choke. At Greenwood, volunteers feed baby birds twice a day, using special formulations and a long dropper.

If a baby bird is found outside the nest, the best course of action is to gently return it and watch to make sure the mother returns. Colorado law prohibits disturbing wild birds or removing them from their nests. Before bringing a baby bird to the sanctuary, it's best to call ahead for advice.

Windholz says that the organization is always in need of volunteers, as there are only five full-time employees. During the busy season, Greenwood adds 12 seasonal paid staff members, 8 to 10 interns, and up to 140 volunteers.

Currently Greenwood staff members and volunteers work in extremely cramped quarters. That will change later this year, when they move into a new facility that is being constructed on their existing site.

Greenwood's new home, which is slated for completion in October, will have 5,247 square feet of space and a new area for water fowl. Thanks to the generosity of two anonymous donors, the land and the building are already paid for.

Fundraising remains an ongoing battle, as Greenwood receives very little in the way of government funding. Annual expenses run approximately $350,000, and are largely funded by individual donors.

Greenwood began a capital campaign in February to raise funds to expand its volunteer and outreach programs, create an endowment, and furnish the new building with badly needed equipment, such as an X-ray machine and other diagnostic equipment. Greenwood has already raised 55 percent of the $2.1 million goal.

There are a variety of ways to support the organization. Financial donations may be made through the Web site, www.greenwoodwildlife.org, and the thrift store in Boulder is always in need of gently used merchandise. Sponsorships are available for individual species, and Greenwood holds a Fall Fest every October.

Windholz, who joined the organization seven months ago, has an affinity for all the animals. She confesses that geese are probably her favorite.

"They have a bit of an attitude," she says.