More Male Birds Than Female Birds

Posted by Rosemary Drisdelle Sep 20, 2007

Surprisingly, it seems that in many bird populations there are more male than female birds, and the smaller the population is, the higher the percentage of males. These are the conclusions, recently published in Ibis, of Dr. Paul Donald, a scientist with the Royal Society for the Protection of Birds.

It’s more than a mere curiosity—these conclusions have significant implications for both research and conservation of bird species:

• Many population surveys focus on male birds—because they are often more vocal and easier to see and identify—and simply count the number of males and multiply by two. This means that many surveys overestimate the total population of a species.
• A greater number of females would be better for species conservation because one male can mate with a number of females (in those species of birds that don’t form exclusive pairs); while the number of offspring a female can produce is limited.
• Female birds are evidently not living as long as males are. They presumably face more threats during migration and dispersion, and are vulnerable to predators while nesting. Dr. Donald suspects that introduced predators, such as feral and roaming cats, play an increased role in predation of females, especially in more threatened species.

If Dr. Donald is right, some of the world’s threatened birds may be much closer to extinction than we believe—conservation work will have to take his conclusions seriously if it is to be effective.

Read the RSPB news item about Dr. Paul Donald’s conclusions: “A Girl for Every Boy?”

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