BLOOMINGTON - Whether the eagle egg at Miller Park Zoo contains a developing embryo remained a mystery after zoo officials made their first close examination of it on Friday. | New video | Eagle cam | Eagle watch

Zoo Superintendent John Tobias and zookeeper Erik Heinonen used a flashlight and an intense television camera light provided by WEEK-TV to "candle" the egg, but its contents were too dense to allow light to pass. Tobias concluded the egg either contains a developing embryo or is rotten and solid.

The egg is the remaining one of two which Beauty, the zoo's female eagle, laid well over a month ago during a four-day visit by a wild bald eagle during its migration.

Beauty shares the enclosure with Mathata, a male eagle. Still, no one knows whether either egg was fertilized.

The injury Mathata suffered that landed him in captivity rendered him unable to balance well enough to mate. The wild bird would have had to overcome its fear of humans and face Mathata.

Zoo officials discovered one egg was missing in mid-May. Speculation centered on a possible theft by a wild animal, such as a raccoon, or a human thief or the chance that Beauty ate the egg after sensing something was amiss.

No one knows which egg, the first or second, remains, so a hatch date cannot be pinpointed. Average incubation time is about 34 days.

At least 42 days had passed in the egg's development when Tobias and Heinonen entered the open-air enclosure Friday.

Unable to fly, Beauty and Mathata scurried away as the humans entered the pen. But Beauty was back, carefully lowering herself on the egg, within two minutes after Tobias replaced it in the nest, which she built on the ground.

The two eggs were her first in 13 years at the zoo.

Tobias said he will now let nature take its course.

The eagles, which share egg-tending duties, eventually will abandon the egg if it is infertile, said eagle expert Given Harper, who heads the Illinois Wesleyan University biology department.

At this point, Tobias called the chances the egg will hatch "less than 50-50."

"Our time frame is kind of running out, but we'll see what happens," Tobias said.

"I'm going to remain optimistic, cautiously optimistic, as long as John says there is a possibility," said zoo marketing coordinator Susie Ohley. "There have been so many twists and turns with this story. I don't think we can give up on it yet."

"If they have a viable egg, they are doing everything they are supposed to do," Heinonen added.

No matter how the story ends, the drama already has had positive results. Zoo attendance is up, said Tobias, who has met many new visitors from around Central Illinois who came to see the birds. Thousands more have visited the Pantagraph's Web site at www.pantagraph.com to watch the eagles via a camera installed in the enclosure by the city.

Teachers Dawn Goldman and Dawn Ludwig from Parkside Elementary School in Normal, who stopped by the zoo to visit the eagles on Friday, said children and adults both have been closely following developments. Ludwig used the eagles' story as a teaching tool when her third-graders recently hatched chicken eggs, she said.

They candled their own eggs. Nine of 12 hatched, she added.

"Everybody is talking about it," Goldman said. "Everywhere you go, the eagles get brought up."