In north america, the spotted owl and the red-cockaded woodpecker are two of the main indicator species. red-cockaded woodpeckers are very picky when it comes to nesting, as they need bigger and thus older trees to create nests. in terms of the criteria for indicator species, they are easy to monitor and count and they are sensitive to specific environmental changes such as a) the influence of pollutants on an ecosystem. b) the health and abundance of old growth forests. c) the amount of predation and competition in their range. d) the decline of species found in their representative food chain.