Taking the helicopter tour in the park involves a small moral dilemma. The noise from the helicopters does scare the wildlife. Park naturalists say that toucans appear only when it's rainy, windy, or fogged in -- days that the copters are grounded. The helicopters are one of two issues over which UNESCO threatened to pull Iguaçu's World Heritage designation (the other was a plan to reopen highway BR-373, cutting the park in half). On the other hand the company has invested in the newest, quietest helicopters. And the view of the falls and canyon from the air truly is spectacular.