Field Museum Study Links Shrinking Madagascar Bats to Hunting

Madagascar's giant fruit bats are smaller today than they were decades ago, and researchers at Chicago's Field Museum say large-scale commercial hunting is the likely driver, according to a study published in the Journal of Mammalogy and reported by the New York Post.

The animals in question are flying foxes, fruit-eating bats with wingspans that can reach five feet, making them among the largest bat species in the world. Comparisons of specimens collected in Madagascar over several decades show a consistent downward trend in body size, the Post reported, citing the study.

How did researchers notice the bats were shrinking?

The discovery began in the Field Museum's own collection rooms. Dr. Emily Cornelius Ruhs, the study's lead author, and colleagues working with preserved flying fox skulls and skins noticed that the older museum specimens appeared larger than the bats the team was encountering during recent fieldwork in Madagascar, according to the Post. That observation prompted a closer, systematic comparison between historical specimens and present-day animals.

"I was thinking about a million different angles to explain why the bats were getting smaller," Ruhs said, according to the Post. "I wondered if it was related to changes in temperature or habitat."

Why do researchers suspect hunting instead of climate or habitat loss?

Ruhs initially considered environmental explanations — shifting temperatures or habitat degradation — as possible causes for the size decline, the Post reported. But a conversation with colleague Dr. Steve Goodman pointed the research team toward a different explanation: selective hunting pressure on the largest individuals in the population.

The reasoning, as described in the Post's account of the study, is straightforward. If hunters preferentially take the biggest bats — whether because larger animals yield more meat or are simply easier targets — the population's average body size would shrink over successive generations as fewer large individuals survive to reproduce. The museum's decades-old specimens, collected before hunting intensified to its current scale, would then appear larger than animals measured in recent fieldwork, which is what the comparison showed.

What is the legal and cultural status of flying foxes in Madagascar?

Under Madagascar's national legislation, flying foxes are classified as a species associated with crop damage because of their consumption of commercially important fruits, according to the Post's report on the study. That classification places them in a category similar to vermin. At the same time, flying foxes are hunted on a large scale in parts of the country as a food source, the Post reported, a combination that leaves the species exposed to significant hunting pressure even as it plays an ecological role as a pollinator and seed disperser.

The study does not describe flying fox hunting in Madagascar as illegal or regulated in the reporting available; it characterizes the practice as large-scale and tied to the bats' status as both a recognized game species and a nuisance animal under national law, per the Post.

What does the size decline mean for the species going forward?

The Post's report on the Field Museum study does not include a population count or extinction-risk classification for Madagascar's flying foxes, and no such figures are cited in the available reporting. What the study does establish, according to the Post, is a measurable, decades-long shrinkage in body size tied by researchers to hunting pressure rather than to climate or habitat changes alone. Researchers used museum specimens — skulls and skins collected and preserved over a long period — as a baseline against which to measure animals encountered during modern fieldwork, a method that allowed the team to track physical change in the species over time without relying on live-population counts from earlier decades.

The Field Museum's collections, the kind of long-preserved specimen archive that made the comparison possible, are a reminder of why natural history museums retain physical specimens rather than only photographs or field notes: the bats themselves, measured side by side across decades, provided the evidence that led researchers from a climate hypothesis to a hunting one.

The study appears in the Journal of Mammalogy. Full reporting on the research, including additional detail on the museum comparisons and the researchers' methodology, is available via the New York Post.