In the stagnant wetlands near the Alewife MBTA station, the bird calls are deafening. Hundreds of wrens swoop through the head-high reeds in dizzy spirals and whorls.

But change is coming for the 90 species of birds, from hawks to owls, that call the wetlands home. The construction of the new Harvard-Smithsonian Center for Astrophysics (CFA) building in Alewife will lead to the removal of some nesting places, but also, community activists hope, open up the wetlands to a much broader range of animal and plant species in one of Cambridge’s wildest spaces.

In addition to the birds, 19 different mammal species, including woodchucks, foxes, and weasels, live near the site of the new building.

A neighborhood group, the Friends of Alewife Reservation (FAR), said they have a commitment from the construction company to preserve the area in a way that will eventually create more biodiversity by increasing the amount of water that enters the swamp.

Ellen Mass, president of FAR, has been working to try to protect the area, a part of the Cambridge Discovery Park, for six years. She said that the organization was excited that the CFA was moving into the neighborhood.

"We are very pleased that they came out," she said, "because we feel that in the long run they will help to preserve this marsh...the last remnant of what they called ‘the Great Swamp.’"

She mentioned the improvement work that Bulfinch Companies, Inc., the developer of the CFA building, has already done in pulling up a concrete parking lot and agreeing to restore four acres of the wetlands.

Eric D. Schlager, Bulfinch Companies’ chief executive officer, said that the work they have done so far to preserve the area "seemed to be a priority."

"We’ve made a pretty significant commitment, though I can’t speak to all of the details," he said.

The 820,000-square foot building is not expected to be completed until around 2010.

FAR is working with the U.S. Department of Agriculture’s Natural Resources Conservation Services to restore Muskrat Marsh, as it is known, to its former glory by making it more diverse, with technical support from the Massachusetts Coastal Zone Management.

Mass explained that the government is particularly involved in the project because the area affects the herring runs around it, which are vital for the well-being of the wider ecosystem.

"Herring are your basic food chain for the ocean," she said. "That’s why the herring that run up and down these tributaries are so important."

For the time being, she said, the work will just involve sampling and data collection, but in the long run they hope to alter the hydrology of the marsh, perhaps by redirecting water through it to relieve the present stagnation and encourage more varied plant growth or by removal of debris and surface regrading. But she added that all these plans are contingent on the financial support they can raise.

"It is so dependent on the funding," she said. "We’re depending on the Bulfinch Company that put up the Smithsonian [CFA building] to pay into this. They have committed themselves to substantially supporting this with their own resources...and there are lots of in-kind and grant donations from others."

The marsh is a rare phenomenon in the highly developed Boston area, a pocket of nature that has survived on the borders of Cambridge and Belmont.

Up to 20,000 birds nest in the area at a time.

Mass said both the forest and swamp were unusual and needed to be preserved. "This is a unique Boston-area forest as it is mainly silver maple," she said. "[It and the marsh] are critical and rare habitats to put together."

She mentioned the lack of involvement Harvard students have had in the area in the past two years and noted how valuable the area could become as a field research space.

Henry M. Cowles ’08, co-chair of the Harvard Environmental Action Committee (EAC) and a Crimson Arts editor, said that FAR has not contacted the EAC to help, and that there are enough groups that do so to occupy them fully.

"It would serve them well to try to reach out and latch on to the students," he said. "[It would be good] to raise the awareness of Harvard students because...they can become disconnected from the place they live in."

Mass agreed with the assessment.

"It is a very special place that Harvard doesn’t even know about," she said.