Study finds sex bias in bird conservation plans

After pairing up and raising chicks, males and females of some bird species spend their winter break apart. At the end of their journey to Central or South America, you might find mostly males in one habitat, and females in another. Yet conservation strategies have typically focused on males and overlooked habitats needed by females, according to a new study in the journal Biological Conservation, putting already-declining species in even more peril.

“Among the small songbird species that have been studied, the general rule seems to be that females occupy lower elevation, shrubbier, drier sites,” said lead author Ruth Bennett, now a postdoctoral researcher at the Smithsonian Migratory Bird Center who conducted the research at Cornell University. “Mid-elevation and high-elevation sites that are more humid and have better quality forest are occupied by males.”

This male-female split is common, Bennett said, but the study found that in conservation plans for 66 declining migratory species, only three made any mention of it. “Overlooking habitats females use can lead to unforeseen population loss,” she said, “which is especially critical for species of conservation concern.”

Using declining golden-winged warblers as their case study, the researchers also found that the landscapes where female birds spend the winter are being degraded more rapidly than those inhabited by males. Field crews surveyed more than 1,100 locations for the warblers during three wintering seasons in Guatemala, Belize, Honduras, Nicaragua and Panama. Researchers then used Global Forest Watch data to see what percentage of areas with the most birds had been deforested between 2000 and 2016. Male golden-wings lost 4% of their habitat during that time. Females lost twice as much, yet the study found that habitats for the males got all the conservation attention.

“To counteract the bias in favor of male birds, researchers and conservation planners need to identify and report the sex of birds, model female distributions, and include female habitats in conservation plans,” Bennett said.

Female birds are often harder to find with their muted colors, and both sexes are quieter while on their wintering locations. But making the effort to consider the needs of female birds could pay off in the long run, she said.

“Yes, it requires more investment and care on the survey portion of any conservation effort when you’re trying to acquire information to guide action,” said co-author Amanda Rodewald, senior director of Conservation Science at the Cornell Lab of Ornithology. “But that could actually allow us to be much more strategic and save money on the back end. Conservation plans are stronger — and more likely to be effective — when they explicitly consider the needs of females.”

Header Image: Male and female golden-wing warblers use different winter landscapes. Researchers found female habitat loss was twice as great as that of males. ©Jack Hruska