(CNN)Researchers have found an unlikely but compelling example of sex bias in the natural history collections of museums around the world.
The fact is that visitors are more likely to find male than female specimens in the Natural History Museum in London or the Smithsonian in Washington.
Natalie Cooper, a researcher from the museum in London, and her colleagues looked at almost 2.5 million specimens from five international collections and concluded that there was a bias towards male specimens. in particular, 40% of the bird specimens and 48% of the mammals analyzed were females.
"We suspected we'd see a bias towards males because science is done by people and people have an inherent male bias," Cooper told CNN via e-mail. "This is especially true as many of our collections come from the Victorian era of macho hunters going out trying to shoot the biggest fiercest creatures for their collections."
More interesting, perhaps, is that the proportion of female specimens hasn't really changed in the past 130 years.
"We were quite surprised by this as we thought things would be getting better," Cooper said. "It could be unconscious bias where people don't even realize they're selecting males, it could be passive in that males are easier to catch or easier to see in the wild, or maybe conservation concerns leading collectors to avoid females."
Cooper said unconscious bias probably played a big role, as both men and women tend to be biased towards males.
Collection methods need also to be considered as a factor for the bias. Males can be showier or larger in the wild, thus easier to collect.
"One good example is the way we usually collect birds. You put up a mist net, then play male bird calls to attract other birds," Cooper said.
"These will mostly be males trying to defend their territories. Although it is studied far less frequently, female birds also call. So maybe using female calls too might help. "
Another issue is that male mammals often range more widely than females, meaning they're more likely to come into contact with hunters, Cooper added.
Collectors are more attracted to large mammals with impressive male features such as horns and antlers. In birds, the bias is towards brightly colored ones. Even for species where the female is the larger or showier sex, the median percentage of females was still smaller -- at 44.6%.
Why does it matter?
But why is it important to have a more accurate male/female ratio in museum collections?
"Our understanding of the natural world is based on what is in these collections, so if they are biased we get a skewed view of the world," Cooper said.
"There are lots of things that vary with biological sex, for example parasite loads, body size and shape, even responses to toxic chemicals."
"If we're only using one sex we won't be getting the correct picture. More broadly, it's also important for people who are visiting museums to see males and females (and everything in between) so they get a full picture of the diversity of life on earth."