Tring and five other museums across the world demonstrate a clear male bias, a study of 2.5million specimens has revealed.
Researchers analysed museum records of bird and mammal collections from 1751 to 2018.
They found bird collections contained 60 per cent male specimens and 40 per cent female. In mammal sections, 52 per cent of specimens were male and 48 per cent female.
The report was written by researchers from the Natural History Museum in Tring and London, as well as the University of Adelaide.
It adds this aspect is often treated as a "nuisance variable, overlooked entirely or data collection focuses on just one sex" and has implications for studies which assume its samples are representative of the whole population or species.
The proportion of female specimens had not changed significantly in 130 years.
“Natural history collections play a critical role in informing multiple research disciplines answering vital questions for the future of biodiversity,” said the researchers.
They said museums should have an awareness of biases within its collections in terms of sex, but also in terms of age and locality among other factors.
"Large studies using museum specimens, especially in vertebrates, are becoming increasingly common and are revealing new insights into the evolution of diversity," the report continued.
"These studies require large amounts of data, which can mean the focus is on collecting data from as many species as possible, to the detriment of other sources of variation.
"Sex is an important factor which influences many aspects of an individual’s ecology and life-history."
The report, published in the journal, Proceedings of the Royal Society B, recommended that museums should acquire material to “best resolve those biases”.
"It is paramount that we continue developing these resources while using a more comprehensive and better-informed approach.
"Researchers investigating broad-scale variation in species should account for these biases when designing data collection protocols and/or in downstream analyses and declare how they dealt with those biases in resulting publications."
The data came from the Natural History Museum; American Museum of Natural History in New York City; the Field Museum of Natural History in Chicago; the Muséum National d’Histoire Naturelle in Paris and the National Museum of Natural History, Smithsonian Institution in Washington DC.