Researchers at UCLA found that adult female birds in North America generally have lower survival rates than their male counterparts.
This finding challenges common biological patterns seen in other animals, such as mammals, where females typically outlive males. Understanding this reversal helps scientists identify the specific environmental and biological pressures that threaten avian populations.
The analysis spanned 27 years [1], utilizing data collected between 1992 and 2018 [3]. To reach these conclusions, the team examined more than 500,000 bird-banding records [2] from across the U.S. and Canada.
Out of 92 Nearctic species examined, females had lower survival rates in 82 of them [4]. Among these, 35 species showed differences that were statistically significant [5].
Researchers said the higher mortality in females is linked to the stresses of migration and reproductive demands. These factors, combined with potential genetic influences related to sex chromosomes, may create a higher biological cost for female birds [6].
The study highlights a systemic disparity in how different sexes experience survival risks in the wild. While males often face risks from territorial competition, the data suggests females pay a higher price for the survival of the species through the demands of breeding, and nesting [6].
“Adult female birds in North America generally have lower survival rates than their male counterparts.”
This research indicates that reproductive investment and migratory stress act as significant drivers of mortality for female birds. By identifying that females are more vulnerable in a majority of North American species, conservationists can better tailor protection strategies to ensure the stability of breeding populations.
