The world’s largest bats have been shrinking for decades, and a new study points to commercial hunting as the likely driver.
Researchers from Chicago’s Field Museum examined 121 Madagascar flying fox specimens collected over the past 150 years and found a clear downward trend in body size beginning around 1980. The giant fruit bats, known for wingspans stretching up to five feet, have been getting progressively smaller according to measurements of skulls and teeth drawn from museum collections across the United States and Europe.
Dr. Emily Ruhs, the study’s lead author, initially suspected something other than hunting was responsible. “I was thinking about a million different angles to explain why the bats were getting smaller,” she said. “I wondered if it was related to changes in temperature or habitat.”
The breakthrough came when Ruhs discussed her findings with Dr. Steve Goodman, the Field Museum’s only full-time field biologist, who has spent nearly four decades living and working in Madagascar. Goodman had examined late 18th- and 19th-century specimens and noticed a striking difference from modern animals. “Many of these animals were of monster size compared to animals we handle today,” he said. “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.”
The timing of the size drop aligned with what researchers believe was the commercialization of bat hunting on the island nation. Under Madagascar’s national legislation, flying foxes are classified as “vermin” due to their consumption of commercially important fruits, and they are hunted for food on a large scale in certain regions. The bats also appear on menus at some roadside restaurants and serve as an important food source for families in portions of the island.
Ruhs performed statistical analysis on Goodman’s measurements and confronted results she found difficult to accept. “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,” she said. The data showed what the team described as a drastic change beginning in the early 1980s.
The researchers believe selective pressure against larger individuals offers a plausible mechanism. “If you’re the biggest bat in the sky, you might be the easiest target,” Ruhs explained. “You’re also going to provide a hunter with the most meat.” Compounding the concern, many of the largest flying foxes identified in the study were older individuals of breeding age, meaning their removal from populations could have cascading effects on reproduction and overall numbers.
Ruhs was careful to note that correlation does not equal proven causation. “Things like deforestation, climate change, inadequate or shifting timing of the fruit season could all be playing a role in making flying foxes smaller than they were 40, 50 years ago,” she said. “I don’t think there’s any one cause that explains it all.” However, the study’s findings suggest human-driven pressure is the dominant factor in the trend.
The research, published in the Journal of Mammalogy, also underscores the scientific value of historical museum collections. Goodman examined specimens held at nine institutions to assemble the dataset spanning a century and a half. “This underlines the importance of historical museum material in helping scientists to understand change through time,” he said. Ruhs echoed that point, remarking: “We can still get a lot of information from these bat specimens that were collected in the 1800s.”
Looking ahead, Ruhs emphasized the need for conservation measures tied to policy changes. “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,” she said. “This needs to involve higher levels of protection following new national laws, particularly at breeding sites, so that the populations don’t collapse.”