BLOOMINGTON - The odds that a live eaglet will be born at Miller Park Zoo were cut in half Friday when one of two eggs laid by the zoo's female bald eagle, Beauty, turned up missing. Eagle Watch

The discovery, made Friday afternoon, is the latest bizarre twist in a story that has captured the heart of Central Illinois.

Miller Park Zoo Director John Tobias said no egg shells or other evidence of tampering was found, adding both eggs appeared healthy and intact on Thursday.

A disappointed Tobias said he has two theories on what might have happened. One involves a four-legged critter, the other a two-legged one.

Tobias said an animal, such as a raccoon, could have invaded the eagle enclosure overnight Thursday and stolen the egg. Miller Park is home to several raccoons. But they've never ventured into the eagle exhibit before, and no evidence was found pointing to an animal as the thief, he said.

Add to that the fear factor, he said.

A raccoon would have had to face two protective adult eagles, Beauty and the male eagle, Mathata, in the open-air enclosure. The birds have shared incubation duties.

"I would think (a raccoon) would have to be pretty brave," Tobias said. "But I would rather think that happened than someone (a human) got in. … I'm not saying someone came in and stole it. I'd like to think no one did, but there were no signs of a raccoon in that exhibit before."

The enclosure's perimeter fence is 8 feet high.

Tobias said zoo staff members found nothing when they carefully searched the grass near the nest. The lawn has been allowed to grow long so mowing will not disturb the birds.

Beauty laid the two eggs a few days apart during a brief visit from a wild eagle, presumed to be a male, that perched over the enclosure periodically over four days in late April. It is unknown if either male bird fertilized the eggs. Incubation period is about 34 days.

The first egg could hatch before or over the Memorial Day weekend. No one knows which egg, the first or the second, remains.

Meanwhile, visitor numbers at the facility are soaring. The zoo has experienced three weekends when single-day admissions topped 1,000 since the drama began, Tobias said.

That benchmark was not reached at all in 2006. Twice as many moms visited the zoo on Mother's Day than on Mother's Day 2006, Tobias said.