Extinction risk factors for New Zealand birds today differ from those of the past. National Evolutionary Synthesis Center, August 2, 2012. What makes some species more prone to extinction? A new study of nearly 300 species of New Zealand birds — from pre-human times to the present — reveals that the keys to survival today differ from those of the past. The results are important for the growing number of studies that try to predict which species could be lost in the future based on what kinds of species are considered most threatened today, the researchers say.