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They discovered about 1,000 breeding pairs on their 240-acre plot, about the same number you would expect to find in a rich forest in eastern North America. However, there the similarities ended. In a North American forest those 1,000 pairs would belong to a total of about 50 species. In Peru the 1,000 pairs represented 245 species, a number approximately equal to all the species known to breed in the entire state of Illinois. Biomass–the aggregate weight of all those birds–equaled 190 kilos per square kilometer, also about five times what you would find in a North American forest.
Parrots move around in single-species flocks. If you are standing in the woods, it is very difficult to count the passing parrots as they move through the trees. So to census the psittacines, Scott Robinson sat in a canoe on the lake and counted them as they passed over in the open sky. The average size of these flocks was taken to be the average size of flocks in the woods, so parrot numbers were computed by multiplying flock sightings by the number of individuals in the average flock.
Tropical animals are often described as rare, and the Cocha Cashu study tends to support that idea. Territories tend to be larger than they are in the temperate zone, so individuals are more widely scattered even in prime habitat.
