Why do men live longer? New study finds male birds outlive female birds

While female mammals typically outlive their male counterparts, a comprehensive new study reveals the opposite holds true for many bird species. Researchers from the University of California, Los Angeles, alongside the Institute for Bird Populations, discovered that adult female songbirds face a roughly 12% lower survival rate than their counterparts.

The research team analyzed over 563,000 capture-and-release records spanning 27 years and 92 North American species. Because most wild birds are caught only once, biologists rely on massive datasets of birds marked with leg bands to accurately calculate how long different species live in their natural habitats. The data showed that across 35 distinct species, females survived an average of 1.36 years after reaching adulthood, compared to 1.61 years for males. While a significant gap existed in only 35 of the 92 species, the males lived longer in 82 of the species studied.

To understand this survival gap, scientists investigated the physical tolls of reproduction, migration, and resource competition. They found that the lifespan disparity was most pronounced in species that migrate over long distances, supporting the theory that female birds endure a heavier physical burden during these strenuous journeys. The data also suggested that male social dominance, which allows males to control access to premium food and shelter, likely contributes to their longer lives. Interestingly, the biological cost of producing eggs did not appear to be the primary driver of early female mortality.

The researchers aim to investigate whether genetic differences play a role, as male birds carry two identical sex chromosomes while females have two different ones — the opposite of mammalian genetics. Understanding why female birds die younger is becoming increasingly urgent, as experts work to determine if ongoing habitat destruction and shifting climates are disproportionately harming the females needed to sustain rapidly declining bird populations.