The National Aviary's expansion will be half of what it had set out to achieve in its 2003 master plan, but the reduction in scale will not hurt programming, said Patrick Mangus, the aviary's executive director.

A $23 million expansion announced last year is now a $17.5 million expansion, "but everything we planned is still being done," he said. The work is expected to be completed by next fall.

Marion Pressley, of Pressley Associates Inc., a Boston firm that worked on the master plan for Allegheny Commons Park, presented a drastic conversion of the aviary's landscaping.

The plan calls for removal of all small flower gardens, Mr. Mangus said. "Her vision was for just trees and grass."

The Historic Review Commission last week approved the revised landscaping plan but raised the issue of what chairman Michael Stern called "a substantial redesign."

For one thing, he said, the previous plan was to use materials to subtly suggest two wings, one on the southwest corner and one on the southeast. With the western expansion on hold, he said, "you have a bird with one wing."

Mr. Mangus said that when funds can be raised to expand both north and west within the aviary's current footprint, some of the original plans can be salvaged.

"The key thing is to upgrade the facilities," he said.

The institution, which sits in Allegheny Commons Park, has been challenged by a lack of visibility and, more recently, a convoluted set of entrances.

"People don't know where to go or how to get in," said architect Bill Szustak, of Springboard Design. An entrance to the gift shop is off the parking lot, but many people walk to the aviary or park on side streets.

On a recent tour of the exterior, Mr. Mangus acknowledged the aviary's counterintuitive entrances. He said the fence that bounds the driveway will be opened to provide a more convenient entry to more pedestrians.

The new design and a dramatic facade will make it obvious that the front of the aviary, and its entrance, are on Arch Street. New construction is expanding most dramatically there, eastward and upward from the glass-sided marsh room. The new construction will house a large classroom, a bird holding area, an elevator tower and a theater, which will have a rooftop area for raptor shows.

The new facade will use perforated metal, backlighting and fritted glass, which has dot patterns that eliminate reflection and should reduce the number of times that birds slam into the glass, Mr. Mangus said.

The new theater will seat 150 and will not have a stage, he said, adding that bird handlers eschewed the idea of a stage. "They want to be out among the people."

The original idea of having a "black box" theater is actually a less agile way to use presentation space, he said.

A cafe that was to have been built on the southwestern side will be inside the existing building, under the dome. The public can patronize the cafe without buying a ticket to tour the aviary.

"We would love to have had the cafe opening into the park and have a seating area overlooking Lake Elizabeth," Mr. Mangus said, shrugging. "But I'm a pragmatist.

"We've done a good job of raising money and decided it is more practical to build what we can from a very good plan."

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