The world’s largest bats are shrinking — and hunters are to blame: study

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The world’s biggest bats are shrinking, reveals new research.

Flying fox fruit bats are getting smaller — and it may be down to human hunters, according to the study.

Comparisons of the bats with five-foot-wingspans collected over time in Madagascar suggest that the biggest ones are selectively hunted, say scientists.

Their findings, published in the Journal of Mammalogy, show that the giant fruit bats have been getting smaller over several decades.

The research team, from Chicago’s Field Museum in the United States, suspects the trend is related to an increase in large-scale commercial hunting.

They had noticed that flying fox skulls and skins preserved in the museum’s collections seemed to be larger than members of the same species they encountered while doing recent fieldwork in Madagascar.

The researchers wondered why the modern bats were smaller than the older ones collected decades earlier.

Study 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 when she spoke to her colleague Dr. Steve Goodman about it, he had a different hypothesis.

On the basis of national legislation of Madagascar, the fruit bats are considered “vermin” associated with their consumption of commercially important fruits.

And flying foxes as a game species are currently hunted for food on a large scale in certain parts of the island nation.

Dr. Goodman, the Field Museum’s only full-time field biologist, has been living and working in Madagascar for nearly 40 years.

He noticed something significant after looking at late 18th- and 19th-Century museum specimens.

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 visited the collections of nine natural history museums across the US and Europe, where he examined 121 Madagascar flying fox specimens that were collected over the course of the past 150 years.

He took measurements of the bats’ skulls and teeth, and then Dr. Ruhs performed statistical analysis of the data to look for overall trends in 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 change was so drastic that at first, Dr. Ruhs believed it must have been a mistake.

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 noted that while the study establishes a correlation between the bats shrinking and the commercialization of hunting, the project so far does not explicitly show that the commercialized hunting caused the bats to shrink.

However, she suspects that it’s no coincidence that the biggest bats were the ones that were disappearing.

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 identified in this study were also older individuals.

If bigger, more mature bats of breeding age are being targeted by hunters, the researchers fear that could affect flying fox populations overall.

However, the team say larger bats being targeted by hunters might not be the only factor in the trend towards smaller bats.

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.”

But the study’s findings suggest that Madagascar’s flying fox populations are shrinking in size largely due to human-driven pressure.

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 said the study also highlights the value of museum collections, adding: “We can still get a lot of information from these bat specimens that were collected in the 1800s.”