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 .…