Officials at the Indianapolis Zoo are preparing for big crowds for the total solar eclipse. But not only are they expecting large crowds, they’re also expecting some activity from the animals, too.

The zoo says on its website that primates have been heard sending calls during the eclipse, and chimpanzees might take a moment to watch the sky.

Zoo educators will be on hand this weekend during xZOOberance at the Zoo. They will teach guests about safe eclipse viewing—and how you can get involved in helping scientists track animal behavior.

Event parking is $30 and free for zoo members. Traffic in Indianapolis and around the Zoo is expected to be heavy on Monday. Officials recommend visitors park before 10 a.m.

The zoo will have extended hours on Monday from 9 a.m. to 6 p.m. They’ll give guests a special pair of glasses to watch the once-in-a-lifetime event.