A sweeping UCLA analysis of North American bird records found that female birds tend to die younger than males — a surprising pattern that appeared across dozens of species and could reshape how scientists think about wildlife decline.
What's happening?
Using more than 500,000 bird-banding records gathered in the United States and Canada from 1992 through 2018, UCLA researchers found that adult females generally survived at lower rates than males. According to UCLA Newsroom, females had lower survival in 82 of 92 Nearctic species, and 35 of those differences were statistically significant.
Joanna Wu, a UCLA doctoral candidate in ecology and evolutionary biology, and her co-authors reported that females survived for an average of about 1.36 years after reaching adulthood, compared with 1.61 years for males — about 12.4% lower survival.
Their paper in Proceedings of the Royal Society B was described as the first large-scale study to compare bird survival rates by sex.
"What was interesting to me was that this pattern was consistent across many different types of birds, from flycatchers and warblers to cardinals and tanagers," Wu said.
The disparity was largest in long-distance migratory species, a clue that migration may place extra strain on females, although the researchers did not settle on one clear reason for the gap.
TCD Picks » Quince Spotlight
💡These best-sellers from Quince deliver affordable, sustainable luxury for all
Why does it matter?
Birds help control pests, spread seeds, pollinate plants in some ecosystems, and serve as visible signals of environmental health.
If females — the birds that lay eggs and sustain future populations — are less likely to survive, that can make it harder for species to recover from habitat loss, rising temperatures, and other pressures.
Communities benefit when ecosystems are stable, farms have natural pest control, and local green spaces support biodiversity. When bird populations weaken, those systems become more fragile.
The pattern runs counter to a familiar one in mammals, where females often outlive males.
"Female birds, in general, are understudied relative to males, so that's what I wanted to research," Wu said.
The study suggests female birds may be bearing hidden biological and environmental costs that make already stressed populations even more vulnerable.
What's being done?
Because most birds are banded once and never seen again, this kind of research depends on a huge capture-mark-recapture dataset. Wu worked with UCLA co-authors Montague Neate-Clegg and Morgan Tingley, along with James Saracco at the Institute for Bird Populations, to analyze records spanning nearly three decades.
They compared the survival gap with traits including migration, wing shape, body mass, clutch size, and social dominance, uncovering some trends but not one definitive cause.
Chromosomes are another possible explanation the researchers want to investigate.
"In birds, unlike mammals, it is the females who carry two different chromosomes, while males carry two of the same," Wu said.
"If the females have already successfully reproduced before they die, their shorter lives might not make much of a difference," Wu said. "But we don't know yet if that's the case or not. We know that habitat loss and climate change are the main culprits."
Get TCD's free newsletters for easy tips, smart advice, and a chance to earn $5,000 toward home upgrades. To see more stories like this one, change your Google preferences here.
