While among mammals, females typically outlive males, a large-scale study has revealed that in many bird species, the opposite trend is observed. An analysis conducted by experts from the University of California, Los Angeles, and the Institute for Bird Populations found that adult female songbirds have about 12% lower survival rates compared to males.

The study analyzed more than 563,000 records of bird captures and releases over 27 years, covering 92 species in North America. Since most wild birds are caught only once, extensive databases of banded birds were used to accurately estimate lifespan in natural conditions. The results showed that among 35 species, females lived on average 1.36 years after reaching adulthood, while males lived 1.61 years. A significant difference was noted in only 35 out of 92 species, but in 82 species, males lived longer than females.

To understand the reasons for these differences, researchers examined the effects of reproduction, migration, and competition for resources. The greatest disparity in lifespan was found among species that undertake long migrations, suggesting that females experience greater physical stress during these journeys. The data also indicated that social dominance among males, which gives them better access to food and shelter, likely contributes to their increased longevity. At the same time, the biological cost of egg production was not found to be the main reason for higher female mortality.

Future research aims to explore the role of genetic differences, since male birds have two identical sex chromosomes, while females have two different ones—the opposite of the situation in mammals. Understanding why female birds die earlier is becoming increasingly important as scientists try to determine whether habitat destruction and climate change are causing disproportionate harm to females, which are essential for sustaining rapidly declining bird populations.