The world’s largest bats are getting smaller, according to new research.
Scientists say Madagascar’s flying fox fruit bats may be shrinking because hunters are increasingly targeting the biggest animals.
The conclusion comes from comparisons with historic specimens featuring wingspans of up to five feet. Researchers found that the largest bats collected in Madagascar over the past 150 years appear to have been selectively removed from the population.
The findings, published in the Journal of Mammalogy, reveal a decades-long decline in the body size of the island’s giant fruit bats.
A research team from Chicago’s Field Museum believes the pattern may be linked to the growth of commercial hunting operations.
The scientists first noticed the difference when skulls and skins preserved in the museum’s archives appeared substantially larger than flying foxes they encountered during more recent fieldwork in Madagascar.
That raised a central question: why were today’s bats smaller than specimens collected decades ago?
Lead author Dr. Emily Ruhs said: “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.”
But after discussing the mystery with her colleague Dr. Steve Goodman, she began considering another explanation.
Under Madagascar’s national legislation, fruit bats are classified as “vermin” because they are associated with damage to commercially valuable fruit crops.
Flying foxes are also hunted for food on a large scale in some parts of the country, where they are treated as a game species.
Dr. Goodman, the Field Museum’s only full-time field biologist, has spent nearly four decades working and living in Madagascar.
His review of specimens from the late 18th and 19th centuries revealed a striking pattern.
Dr. Goodman said: “Many of these animals were of monster size compared to animals we handle today.
“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.
“This underlines the importance of historical museum material in helping scientists to understand change through time.”
Dr. Goodman examined collections at nine natural history museums in the United States and Europe, studying 121 Madagascar flying fox specimens gathered over roughly 150 years.
He measured the bats’ skulls and teeth, while Dr. Ruhs analyzed the data statistically to identify long-term changes in body size.
She said: “We took all those measurements and put them together, and we looked at how they changed over time.
“We saw a clear drop in size starting around 1980, when we believe bat hunting became more commercialized.”
The decline was so pronounced that Dr. Ruhs initially suspected an error in the analysis.
She said: “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.”
Dr. Ruhs stressed that the research demonstrates a relationship between shrinking bats and the commercialization of hunting, but does not yet prove that commercial hunting directly caused the decline.
Still, she believes it is unlikely to be a coincidence that the biggest bats were also the ones disappearing most rapidly.
Dr. Ruhs said: “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.”
Many of the largest flying foxes in the study were older animals as well.
If hunters are disproportionately killing larger, mature bats of breeding age, the practice could have consequences for the health and stability of flying fox populations.
However, the researchers caution that selective hunting may not be the only reason the bats are becoming smaller.
Dr. Ruhs said: “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.
“I don’t think there’s any one cause that explains it all.”
Even so, the study points to human pressure as a major factor behind the decline in the size of Madagascar’s flying foxes.
Dr. Ruhs said: “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.
“This needs to involve higher levels of protection following new national laws, particularly at breeding sites, so that the populations don’t collapse.”
She added that the research demonstrates how valuable historic museum collections remain, saying: “We can still get a lot of information from these bat specimens that were collected in the 1800s.”
