Eastern Red Bats, moths, and leaf litter

Hi all, and thanks as always for reading! Sorry for the long (for me) lapse in posts. Things have been a bit busy of late, and it's been tough to carve time out to sit down and craft a new piece. But here we are, and away we go.

An Eastern Red Bat (Lasiurus borealis) nestles among the leaves of an American Beech (Fagus grandifolia). This species is the consummate tree bat, and its range mirrors that of the great eastern deciduous forest, which spans the eastern half of the U.S., stretching from the Gulf Coast into southern Canada.

Shauna Weyrauch and I have had some interesting field excursions of late, two of which involved inspecting relatively small woodlands in central Ohio. In one, we found the bat pictured above, and in the other, we found not one, but two bats ensconced in a beech. These experiences got me thinking a bit deeper about the tiny bats (as little as 10-12 grams! About the same weight as a Song Sparrow!).

A young American Beech in a Franklin County, Ohio woodland. Beech typically retains many leaves throughout the winter, and they are still on the tree come spring. Also note the rich leaf litter on the forest floor. By the way, the Red Bat pictured above is in this photo, towards the far-left side of the leafy limb that sticks out the furthest. It looks like a little dark blob.

We move in a bit closer, and now you'll probably see the wee mammal. After one gets the search image, it isn't too tough to spot roosting Red Bats - if you're giving the trees the once-over. Beech seems to be the best host, at least that's the plant that I've found most of them in. They likely hide among long-persistent oak leaves as well and are known to roost on the ground buried in leaf litter. I once saw one making aerial hunting forays during the day and the bat would return to hide under exfoliating bark high in a hickory between runs. But beech may be the easiest to find them in, and it's always worth giving trees like the one above a good look.

A Common Oak Moth (Phoberia atomaris) rests in leaf litter. As soon as we entered this woods, we began flushing moths from the litter. As it was pretty early - March 14 - I was keen to know what they were. Not many moths are yet out. It didn't take too long to get an answer, and we went on to see many of these oak moths. It seemed that every we flushed and saw well was this species, and that was quite a few.

Moths that emerge this early - this species overwinters as pupa in leaf litter - may be tied to early spring sap flow in trees. There are few if any floriferous nectar sources yet available, but sap provides a ready source of sugar for energy and a number of moth species visit oozing sap.

Face on with an Eastern Red Bat. Moths are the number one prey group for eastern bats, and relatively hefty oak moths as in the previous photo would make quite a meal for the little mammals.

I was especially interested in the potential moth-bat link as I've never encountered Eastern Red Bats in March and think of them as largely an April/May phenomenon. A quick glance at iNaturalist also shows many more April than March records at this latitude.

Red Bats are migratory, and it's thought that the majority of bats at northerly latitudes, including Ohio, migrate to southeastern states for the winter, and return in spring. Perhaps the earliest returnees are synced to arrive when very early spring sap-feeding moths emerge? These March sap-feeders are quite hardy and can fly in low temperatures. I once saw scores of Morrison's Sallow moths (Eupsilia morrisonii) flying about a northern Ohio woodlot on a March night when temperatures were in the mid-30's.

Another possibility is that the bats that we are encountering in early/mid-March are ones that overwintered. My hunch, though, is that they are migrants moving north with the first warm days, as the weather was in the 60's and even low 70's F for a few days preceding our observations.

An Eastern Red Bat tucked into senescent beech leaves.

A great many moths (bat food) are highly dependent upon leaf litter. As noted, the Common Oak Moth pupates in leaf litter, and habitually hides in it during the day. When flushed, the moths quickly return to the litter and often scuttle under the leaves. The aforementioned Morrison's Sallow overwinters as adults, but probably also spends its days hiding among leaf litter, along with numerous other species. There is even a subfamily of moths known as litter moths, as the caterpillars feed on dead leaves.

Leaf litter spawns lots of bat food in the form of moths. Fortunately, we don't generally have to worry about the leaf-blower crowd taking to the forest. But those dastardly devices do enough damage in areas where leaves should remain. Even suburban/urban gardens can produce plenty of moths if leaves remain in garden beds and other places where there is no reason to blow them away.

It remains to be seen how the continuing onslaught of nonnative invasive earthworms will impact moth production. These worms can transform an ordinarily leafy forest floor to bare dirt in short order. I've seen the effects, and it is dramatic. Presumably, such litter decimation has an adverse impact on litter moth production and by extension bats. If you aren't familiar with the worm issue, CLICK HERE.

Be sure and scope out any leafy beech you might encounter this spring. Look for little dark reddish blobs among the senescent brown beech leaves. The odds of finding one probably increase if a stream is nearby, as bats often hunt over stream corridors at night. Search enough beech and sooner or later you'll turn one up. It's a magical experience.