BLOOMINGTON - Zoo workers may take a closer look at an eagle egg at Miller Park Zoo if an eaglet doesn't hatch before Friday, zoo director John Tobias said Tuesday. | New video | Eagle cam | Eagle watch

Tobias said he may "candle" the egg, a process in which light is shined through the shell to see what's inside. Closer examination also will reveal if an eaglet tried to break out. Birds sometimes fail to escape the shell and die, he said.

"It's time to take a closer look," Tobias said. "One way or the other we have to resolve this."

"They are both staying really protective. I haven't given up hope," added Susie Ohley, the zoo's marketing coordinator.

Beauty, the zoo's mature female eagle, and her companion male, Mathata, continue to take turns incubating the last remaining egg of two Beauty laid in a four-day period in early May. The eggs were the first Beauty laid in her 13 years at the zoo.

One egg disappeared from the nest because of another animal or human intruder, or if Beauty herself sensed something was wrong with the egg's development and ate it.

The average incubation period for bald eagles is 34- to 38 days.

"If this is the second egg, it's still in a potential time frame," said Given Harper, an eagle expert and head of Illinois Wesleyan University's biology department. "It's roughly day 39, and it could go to day 40. But, once you get beyond day 40, that's a pretty good indication the egg won't hatch. By the end of the week, you'll have a pretty good idea."

Harper thought the egg's viability was slim from the start. Mathata, unable to fly because of earlier injuries, would have difficulty balancing enough to fertilize Beauty, he said.

Harper also thinks a wild eagle that visited the zoo during the four days the eggs were laid would have been unlikely to overcome its inherent fear of humans long enough to drop into the open-topped eagle enclosure and fertilize the eggs.

Because Mathata has assumed parenting duties, Harper said Mathata and Beauty have evidently formed a bond that would have sparked Mathata to try to fight off the visitor, he said.

Zoo staff saw no evidence of a struggle.

"I hope the egg is fertile and it will hatch," Harper said. "Given the circumstances, my gut feeling is that it's infertile, but I fervently hope I'm wrong."

If the egg is infertile, Beauty could incubate it for a week or two longer before losing interest and abandoning the nest, Harper said.

Interest in the egg is intense everywhere Tobias goes, he said. When his wife, Rosalie, fell and hurt her shoulder about a week ago, the emergency room doctor asked Tobias about the status of the egg before he asked questions about his wife's injury, Tobias said.

A dentist who was examining his wife earlier this week also came out to the waiting room to ask about the egg.

Tobias remains optimistic and says a golden eagle egg hatched recently at the Topeka, Kan., zoo. "I'm still hopeful," Tobias said.

Ohley said visits to the local zoo have soared. May attendance of 21,300 visitors was the highest recorded for a month of May in at least five years. May 2006 saw 15,634 visitors and May 2005 saw 18,983.