A new study published in the ornithological journal Ibis has uncovered that for the vast majority of bird species, there are more males than females. The discovery suggests that populations of many of the world’s threatened birds could therefore be overestimated, because scientists often base population estimates on counts of males.  The headline above, cribbed from the BirdLife International article on this topic, may evoke images of lurid avian brothels, but the implication is that introduced predators often kill female birds when they are incubating eggs in the nest.