You are what you eat – how diet influences spine mobility in Neotropical bats

Bats are an incredibly ecologically diverse radiation of mammals that inhabit a wide array of ecosystems, have a variety of locomotor and navigational strategies, and consume many different types of food. We expect teeth and jaws to be shaped by diet because they are directly used to consume food. Bats, however, have furthered their dietary specializations to include their flight habits and locomotor anatomy. For example, animalivorous bats who glean stationary prey from vegetation tend to have short, wide wings to better navigate cluttered spaces, in comparison to those who capture flying prey and require greater aerial agility.

Part of that aerial dexterity includes the head and neck. Aerial foragers, for example, have been observed using their tail membranes to bring prey to their mouths, a behavior that should require a very flexible spine. Frugivorous bats, on the other hand, often carry fruits in their mouths to a preferred roost to consume, a behavior that likely requires robust neck musculature and a stiffer spine.

My collaborator, Dr. Andrea Rummel, and I (Fig. 2) were interested in understanding how dietary habits influence head and neck range of motion in bats. To test our hypothesis, we went to Lamanai Archaeological Reserve in Belize where Drs. Nancy Simmons and Brock Fenton organize a long-standing field trip dedicated to bat research, informally dubbed the ‘Belize Bat-a-thon.’ Orange Walk County, Belize, is home to dozens of bat species including the vampiric Desmodus rotundus (Fig. 3), the fishing bat Noctilio leporinus, who use their feet to snatch fish out of the water and scoop it into their mouths with their wings, and Saccopteryx bilineata whose male members have forearm sacs that produce a pleasant odor used to attract females. Many of these species use the archaeological ruins as roosts and the parkland surrounding the ruins offers a refugium for local wildlife, including howler monkeys.

The research team set up mist nets every night at dusk to catch bats as they left their roosts in search of breakfast. We then returned to the ‘lab’ where researchers collected all kinds of data from fecal samples to body temperatures for various research projects. We relied on noninvasive methods to gently, but firmly, manipulate the head into its maximum ranges of motion with a wooden dowel while holding the trunk steady. Some bats were more willing research participants while others weren’t afraid to screech their displeasure. Although spinal range of motion is best measured using radiographs, getting an x-ray machine setup in the field would be tricky and so we relied on photography. Once we were finished, the bats were released into the night to find their way home or their next meal