Most outdoor festivals and events have a proviso stating “rain or shine,” assuring ticket buyers that the event will go on for as long as it can. But what about endangered species? A new challenge faced by Mamby on the Beach in Chicago threatens the event’s venue.

A pair of endangered piping plovers who have built a nest at Montrose Beach has gained the attention of bird conservation groups lead by the Chicago Ornithological Society, as well as the Montrose Lakefront Coalition, which is seeking to have the festival moved away from the Montrose Beach area. The birds have laid four eggs, an event which Chicago Sun Times calls “a rare and cherished occasion among birders.”

Jerry Mickelson, who heads up concert organizer JAM Productions, sent a letter to MLC that read, in part: “Why do you feel that MAMBY music fans do not have the right to enjoy Montrose Beach just like others do? Who appointed MLC as gate keeper?”

He went on: “Let me warn you that there are millions of dollars at risk here and all of you might be exposing yourselves to this liability by your interference with our right to hold this event at Montrose Beach that you have requested/insisted the park district not allow.”

The original four eggs were moved into the protection of the Lincoln Park Zoo after high water threatened them earlier this week, but the plovers appear undeterred and once again engaging in courtship activities. Should they lay another set of eggs, the chicks likely wouldn’t learn to fly until late August, stated Jill Niland of MLC.

The musical festival is scheduled to take place on Aug. 23 and 24 and expected to draw as many as 20,000 people to the lakefront each day, which raises concern over “waves of people and noise pollution from three stages disrupting the piping plovers and any potential offspring.”

No decision has been made at this time.