In the column “Since You Asked” in every issue of BirdWatching, Contributing Editor Julie Craves answers readers’ questions about birds and bird behavior. Here is a question from our October 2014 issue:
I’ve noticed that, among cardinals, more males than females show up at my feeder. Are the females shyer, or is there another reason they avoid the feeder? — Chase Proctor, Columbus, Ohio
You may be observing the phenomenon that the adult sex ratio in many bird species skews toward males. In a large study, adult males outnumbered females in about 60 percent of songbird species. Generally, the ratio of male to female chicks in the nest is about equal; the major cause of the male bias in adults is female mortality.
Female birds tend to have higher mortality rates for several reasons: Egg production is physically demanding, and in most songbirds, the female is the incubating parent. Incubation not only puts her at a higher risk from predators but also is an energetic strain.
Migration is always perilous, and in migratory species, the smaller sex tends to fly farther; in many species, this is the female. Differences in where and how each sex forages can also make females of some species more vulnerable to predation. — Julie Craves
About Julie Craves
Julie is supervisor of avian research at the Rouge River Bird Observatory at the University of Michigan Dearborn and a research associate at the university’s Environmental Interpretive Center. She writes about her research on the blog Net Results, and she maintains the website Coffee & Conservation, a thorough resource on where coffee comes from and its impact on wild birds.
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