The secrets of island bats

Submitted by Kwiaht

What do our Northwest bats eat? The simple answer to this question is insects, but that is about as useful as saying “animals.” There are more than a million species of insects on earth, and nearly 100,000 of them live in North America. Humans regard some insects as pests, some as beneficial, some (like many beetles and butterflies) as simply beautiful, and most of them as simply irrelevant. Most people assume that bats prefer to eat the most annoying insects, such as mosquitoes; but do bats share our perspective?

Imagine the challenges faced by hungry bats. Our island bats are very good at targeting and intercepting insects on the wing, but staying aloft takes energy. Bats need to maximize the number of calories they can collect per minute of flight time. This may mean seeking a few large buttery insects such as moths, or large swarms of smaller, less calorie-rich insects such as midges and mosquitoes. Swarms of large greasy insects such as termites are best of all, but they cannot be found at all most of the year. Even on a warm summer evening, moreover, flying insects are not evenly distributed everywhere.

Do our bats communicate hunting knowledge to each other? Do younger, inexperienced bats follow older bats to see where they hunt? Or is it “every bat for herself?” At this stage, we really do not know.

One of the emerging challenges for island bats will be adapting to the effects of climate change on the emergence timing of prey species. Indeed, we may see some insect species move farther north as the Salish Sea warms, to be replaced by insects that our islands’ bats have never before hunted.

Software capable of unscrambling bats’ voices and identifying individual bats in a feeding frenzy over a marsh has only existed since 2009. New-generation software using cluster analysis to identify thousands of bat calls in minutes is indispensable to Kwiaht’s network of five bats “listening posts” around San Juan County. On a typical summer evening, Kwiaht’s Bat Grid will record about 2,000 bat flyovers, representing nine species of bats.

One unmistakable finding of Kwiaht’s Bat Grid is that a lake, pond or woodland clearing is visited by different bat species at different times of the year.

These dense data sets still lack one very important variable: the target insect species. How can researchers tell what the bats circling over a particular marsh one night are actually eating?

The conventional solution has been to set out insect traps to sample the “prey field,” then trap some bats and detain them until they defecate. Fecal pellets (guano) consist of finely chewed insect exoskeletons, some of which can be identified by a meticulous, sharp-eyed entomologist with a microscope. Over the past few years, however, a small number of laboratories (including Kwiaht’s Lopez lab) have begun using the residual traces of DNA in guano to identify the insects eaten, and sometimes the bat species as well.

Kwiaht researchers also collect guano from beneath known bat roosts. Collection sites include bat houses constructed by Kwiaht for displaced maternity colonies.

The latest development in bat research technology is a smartphone microphone and app that makes it possible to do “point and shoot” species identification of bats in flight. The next phase of bat research, still in development, involves identifying insects acoustically. Many insects also echolocate, or have distinctive flight sounds that could be recorded and decoded.

Watch for announcements next spring and summer of Kwiaht “bat viewing nights” when researchers will demonstrate the new technology for identifying bats in real time “on the fly” as they feed on swarms of insects. And ask Kwiaht about less expensive versions of this technology that can convert your smartphone into a bat detector! Batting can be as much fun as birding if you have the technology to eavesdrop on bats and identify them.