Echolocation & Evolution: How Bats Continue to Redefine Their Diets and Adapt to the Night

Whether they are frugivorous, insectivorous, or subsist on other foods, all bats fly and most bats echolocate. They navigate and find prey by emitting sounds and listening for the returning echoes as they bounce off trees, walls, and even flying insects. For bats to have achieved this version of sonar, the bones in their skulls evolved to give extra support to their throat muscles and voice boxes, enabling them to create high-frequency echolocation calls. They also evolved large cochleas, the inner portion of the ear containing nerve cells that transmit to the brain, which helps them better hear and distinguish the ultrahigh pitch echolocation calls.

A hot debate continues to rage in the scientific community on which came first: echolocation or flight? Since bats have one of the poorest fossil records of any group of mammals, we still don’t know the answer. Some argue that flight evolved before echolocation in bats, others argue that echolocation came first, and another argument is that they evolved together.

Recent evidence, however, from the oldest, well-preserved bat skull suggests that  bat ancestors evolved echolocation before they evolved true flight. They may have lived and glided among trees, using echolocation for general orientation at night, rather than depending on sight, like other most other nocturnal animals.

If owls, and other nocturnal predators, evolved large eyes to see and hunt at night, why didn’t bats do the same? It seems that the common ancestor of bats had small eyes that weren’t well suited for hunting prey in dim light and may have possessed a brain predisposed to evolve echolocation. Further, echolocation proves to be better at navigating and hunting in the night skies. Recording the sounds bounced off insects, scientists determined echolocation to be twice as effective as vision when it comes to finding prey in dim or dark conditions. They found that vision detected insects up to 20 feet away, but echolocation could detect them 40 feet away. Pinpointing prey by echolocation was unhindered by trees, brush, or other objects in the environment. It is also more effective than sight at estimating the distance and velocity of prey.

If humans ate nothing but figs, bananas, and mango, we would inevitably suffer from cavities, high blood sugar, and malnutrition. So how can some species of bats gorge themselves on nothing but fruit without suffering similar ailments? Fruit bats evolved pancreases with more insulin-producing cells, keeping their blood sugar even, despite their diet. They also produce extra glucagon, a hormone that regulates sugar. Their kidneys have adapted to trapping salts, which aren’t plentiful in fruits. As for removing fruit from trees, leaf-nosed fruit bats evolved face shapes with a shorter snout, giving them a stronger jaw to chomp on hard fruits like figs, and lots of variation in head shape is linked to high species diversity.

Nectarivores have evolved to consume the nectar of flowers and thus serve as pollinators. Research indicates that the bat-pollinated flowers were originally pollinated by other mammals, with bats later taking over this role. Natural selection has shaped nectarivorous bats to have long, specialized tongues to reach nectar deep inside flowers. Additionally, co-evolution has shaped the flowers to precisely deposit pollen on their pollinators to increase the chance of successful pollination.

Apparently, it takes a big nose to be at the top of the food chain! Carnivorous bats have evolved longer snouts, probably to more easily take down rodents, birds, or other animals that make up their diets. Longer snouts also enable them to quickly tighten their jaws around prey striving to escape. The fish-eating bat nets its prey with a shorter, wider snout that projects slightly upward, an adaptation well suited to catch and hold onto slippery fish.

The most specialized diet of all bats is sanguivory (drinking blood!). Of the 1400+ species of bats, the three species of vampire bats most likely descended from an insectivorous ancestor. As they evolved, these bats developed many specializations for this unique diet, including many adaptations to manage the low nutritional quality of the food, particularly in their kidneys, an ability to excrete high levels of iron, and specialized heat-sensing pits around their noses, similar to the heat-sensing pits on pythons and pit vipers. Vampire bats use these organs to find warmer areas on their hosts’ bodies, which have more abundant blood flow and offer a ready meal.

Exciting new research from a 2014 BCI Student Scholar, Dr. Tyrone Lavery, shows that bats continue to evolve today. DNA evidence reveals leaf-nosed bats in the Solomon Islands have recently, and more than once, evolved larger versions of themselves, perhaps to catch larger prey. The scientists say that although the larger and smaller bats may live in the same caves, they may no longer recognize each other for mating.