The puppy-sized bats of Madagascar are shrinking

The winged mammals boast five-foot-wide wingspans. Image: Sylvain Cordier / Contributor via Getty Images It’s the stuff of nightmares. A bat the size of a large-breed puppy with five-foot-wide wingspans darting across the sky. But don’t worry. The giant flying foxes want fruit, not your blood. However, biologists do have something to worry about regarding these enormous winged mammals. Madagascar flying foxes (Pteropus rufus) are shrinking. They have been getting smaller over the past several decades, which biologists suspect may be related to an increase in large-scale commercial hunting. A study published today in the Journal of Mammalogy details the findings. While sifting through a collection of preserved flying fox skulls and skins at the Field Museum in Chicago, the study’s authors noticed that the specimens in the archive appeared larger than those they had seen during recent fieldwork in Madagascar. They were not sure why the modern bats were so much smaller than those previously collected. To help exemplify the overall phenomenon of flying foxes shrinking, two specimens from the Field Museum’s collections. The smaller specimen on the left is from 1995; the larger specimen on the right is from 1948. Image: © Field Museum. “I was thinking about a million different angles to explain why the bats were getting smaller. I wondered if it was related to changes in temperature or habitat,” Emily Cornelius Ruhs, a study co-author and wildlife ecologist at the Field Museum’s Negaunee Integrative Research Center, said in a statement. Ruhs spoke about this puzzle with her colleague and study co-author Steve Goodman, and he had a different idea in mind. These fruit bats are legally considered vermin in Madagascar, and are often associated with eating commercially important fruits. They are also a game species, and hunted for food at a large scale in parts of the island nation. Goodman, a full-time field biologist, has been living and working in Madagascar for nearly 40 years. After examining the late 18th and 19th century museum specimens, he noticed that many were a “monster size” compared to the animals handled in the wild today. Malagasy flying fox (Pteropus rufus) hanging upside down in its roost tree in Berenty Private Reserve, Madagascar, Africa. Image: Liz Leyden via Getty Images. Liz Leyden “Hence, the idea was formed that they have diminished in body size as a result of recent heavy hunting pressure and they are not living as long as they did in decades past,” Goodman added. “This underlines the importance of historical museum material in helping scientists to understand change through time.” To investigate further, Goodman visited the nine natural history museums across the United States and Europe. He examined 121 Madagascar flying fox specimens collected over the past 150 years, measuring the bat’s skulls and teeth. Ruhs then performed statistical analyses, to look for overall trends in size. Emily Cornelius Ruhs measuring the skull of a Madagascar flying fox in the Field Museum’s collections. Image: © Field Museum. The team saw a clear drop in size beginning around 1980, when bat hunting likely became more commercialized. This change was so stark that Ruhs initially thought there must be a mistake. “I thought that there must be something wrong with the analysis, there was no way that the rough estimate we had was correct, but it was,” Ruhs recalled. While the study establishes a correlation between the bats shrinking and the commercialization of hunting, the team is not not explicitly showing that the commercialized hunting over 40 years caused the bats to shrink. But Ruhs suspects that it’s not a coincidence that the largest bats were the ones that were disappearing. “If you’re the biggest bat in the sky, you might be the easiest target. You’re also going to provide a hunter with the most meat,” said Ruhs. Additionally, many of the largest flying foxes in this study were older individuals. So if bigger, more mature bats of breeding age are being targeted by hunters, that could affect flying fox populations overall. Targeting larger bats might not be the only factor in the trend towards smaller bats. Deforestation, climate change, human activity, and shifting timing of fruit season could be playing a role at the same time, and not one cause. “These bats are an important food source in certain portions of the island for people to feed their families or on the menu in some roadside restaurants, so it is critical to figure out ways to protect the bat populations,” says Ruhs. “This needs to involve higher levels of protection following new national laws, particularly at breeding sites, so that the populations don’t collapse.” 2026 Popular Science Home of the Future Awards 39 products that will improve your everyday life.