It is one of the most famous museums in the UK, with its exhibits drawing visitors from around the world. But the Natural History Museum in London is one of five world-renowned museums whose exhibits have a slight bias to the male of the species, which risks negatively impacting science.
The researchers who examined two million species in five museums worldwide argued that by leaving out members of the animal kingdom who are female (such as leopards and lions), this is bad for science.
They claim it is harder to classify females into the correct species when there are not enough exhibits to refer to.
Male birds outnumbered female birds by 60 per cent to 40 per cent and mammals were 52 per cent male and 48 per cent female.
Museums house what's known as reference animals - the official specimen for each species to which new animals must be compared. Among these animals, only 27 per cent of birds and 39 per cent of mammals in the reference animals were female.
The study is published in the journal , Proceedings of the Royal Society B, and it calls for the gender imbalance to be redressed.
It found if collections "are biased towards one sex, studies may not be representative of the species."
And the proportion of female specimens has "not significantly changed in 130 years, but has decreased in species with showy male traits like colourful plumage and horns".
The study concluded "curators and collections managers" do not as a rule discard specimens based on sex, therefore any bias is likely related to "what is collected in the field".
In some collections males are "larger or more colourful" than females or possess ornaments or weaponry "such as horns or antlers".
Dr Natalie Cooper, of the Natural History Museum, in London, who authored the report, said: "There is a tendency for the people collecting to want to get the largest grizzly bear or the animal with the most impressive horns."
The animals were all collected between 1751 and 2018, but things didn't improve over time.
Dr Cooper added: "Interestingly, we see no improvement. Even recent collections are biased."
The researchers also looked at the Smithsonian National Museum of Natural History in Washington DC, the Field Museum in Chicago and the American Museum of Natural History in New York, as well as the National Museum of Natural History in France.