(CBS) — For the next three months or so, the purple martins are visiting Chicago. So far, the city is seeing far fewer than in recent years.

Almost every purple martin that comes to Chicago stays in a manmade tower — a high-rise apartment of sorts.

Five of the towers are at Montrose Harbor, where the park district’s volunteers (nicknamed “landlords”) count the birds. Later, they count the eggs.

“I ask all my landlords to wear a hat, and I even encourage them to get a red one. When they see me, they know me,” says Michael Karagianis , lead volunteer/landlord at Montrose.

Purple martins at Montrose Habor (WBBM)

He describes the purple martin’s calls this way: “Choo-choo-choo. And then click-click-click. Five choo’s, and then three clicks.”

Karagianis has been documenting the purple martins at Montrose for 10 years.

“This year we’re down, terrifically down. Fourteen — that’s nothing.”

Volunteer Michael Karagianis with Forrest Cortes, Community Stewardship Program Manager with the Chicago Park District. (WBBM/Steve Miller)

It’s not clear why. The Chicago Park District says it’s probably related to food supply, perhaps fewer insects.

More purple martins could come in the next couple of weeks.

The Chicago Park District is looking for more volunteers as purple martin monitors.  For more information, contact Forrest Cortes, forrest.cortes@chicagoparkdistrict.com.