A new study finds that overlooking the lives of female birds can have severe conservation consequences
I’ve long wondered why so many ornithologists, conservation biologists and birders ignore or overlook female birds. For example, I’ve often found a lot of challenge as well as pleasure in identifying and observing female birds as they go about their lives – lives that are different from those of the (sometimes) more showy males of the species.
This sex-bias was explored by conservation biologist Joanna Wu, a PhD student in Ecology and Evolutionary Biology at UCLA, in collaboration with the Audubon Society. In this study (ref), Ms Wu, whose research focuses on female birds and conservation, argues that improving identification and observation of female birds can help scientists to better conserve birds and their habitats.
“There is so much more that we can learn about birds, and about ecology in general, that we miss when we only focus on males, or assume that females are ‘similar enough’ to males,” said Ms Wu, the study’s lead author. “That’s why it’s so critical that we encourage sex-specific questions in research.”
For example, Ms Wu and collaborators argue that our knowledge of birdsong is strongly biased: it is based on northern hemisphere songbirds and thus, does not apply to birds living in the tropics or in the southern hemisphere, where typically, both females and males sing (ref).
“It shocked me how much of our assumptions about female birds are based on males (largely from Europe or North America) [are] simply false,” Ms Wu told me in email.
Additionally, Ms Wu and collaborators find that female song is probably the ancestral state in 71% of species globally and is present in 64% of bird species with sex-specific songs (ref and ref).
Further, Wu and collaborators assert that, contrary to our now outdated notions, both sexes participate in incubating and raising offspring in many bird species. Our sex-based biases, probably derived from human preconceptions of how the natural world works, are ideas that may have gained support from Charles Darwin’s influential writings (The Descent of Man and Selection in Relation to Sex; Darwin 1872). Moveover, observations of species where females are socially dominant or aggressive, such as shorebirds and raptors, are underreported and understudied (ref).
Wu and collaborators also report that, unlike in mammals, female birds often have a lower survival rate than do males of the species (ref and ref) – a trait that can have powerful negative conservation effects, particularly in endangered species (ref and ref). This observation likely results from female birds being the heterogametic sex (ref), as well as females bearing higher reproductive costs (ref) than males, having higher natal or post-breeding dispersal (ref), and reduced or limited access to essential resources due to male social dominance (ref). For these reasons, important sex-specific information can be obscured when researchers average survival rates across sexes in their studies.
Another important factor that Wu and collaborators point out is that female birds may have different migration or overwintering patterns – details that can be critically important in light of climate change because changing temperatures could result in, say, a mismatch of arrivals at breeding grounds or in different ecological pressures. For example, we know that female golden-winged warblers overwinter at lower elevations than males, and due to logging biases, females have lost twice as much of their winter habitat than have males. Thus, carefully considered and balanced research analyses can help inform conservation efforts.
But really, many sex-specific questions remain unexplored, particularly regarding habitat use in the non-breeding season. For example, we know that migration routes, stop-over sites, and habitats differ for some bird species by age and sex (ref), but we know almost nothing about the details.
How can these inequities be addressed? Wu and collaborators recommend that improving knowledge about female identification, capturing birds during migration rather than during breeding season to increase the likelihood of observing and studying females, and including options for birders and citizen scientists to record sex-segregated data in apps like eBird to inform major ornithological institutions.
“To get a more complete picture, scientists should sample from both sexes and be aware not to lump the data that they are collecting without testing for differences,” Ms Wu advised in email. “In Figure 1, we provide eight recommendations for collecting data more equitably.”
It’s important to be aware that, like people, birds are not two-dimensional cardboard cutouts. Basically, if you exclude a whole gender, or race, or social class, you’re going to miss a whole perspective and way of seeing and experiencing things.
“The most important message is to be aware that the biology of birds (whether we’re talking about migration, reproductive roles, survival, climate effects) differs by sex,” Ms Wu explained in email.
There’s so many things to think about with regards to these findings; what surprised you most?
“The most surprising thing to me is that survival rates differed by sex,” Ms Wu told me in email. “I wonder what downstream effects this has, like on population growth rates. In an era of widespread population declines, knowing there are sex differences in how birds survive can be a tool for conservation and management.”
Source:
Joanna X. Wu, Martha A. Harbison, Stephanie Beilke, Purbita Saha, and Brooke L. Bateman (2025). A focus on females can improve science and conservation, Ibis | doi:10.1111/ibi.13386
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