Boat Tour of the Upper Dells, Wisconsin (2)

The tour guide explained that swallows returning from Venezuela like to peck at existing holes in the bedrock, enlarging the holes so that they can build nests in them. The residents of Wisconsin Dells are happy to see these birds returning because they eat mosquitoes. Of course, the birds cannot eat all of the mosquitoes. The mosquitoes that are not eaten are captured humanely and released in Minnesota.