Bat habitats

The very large increase in codling moth damage in the Eaton Rapids orchard seems like an anomaly because we have rarely had much.

At two o'clock this morning, I had an "Ah-ha!" moment. Early this spring I removed the old, decrepit, seemingly un-used bat nesting habitat from our orchard. It was a skirt of black, roll-roofing around an abandoned-in-place utility pole. Some fence had been stapled to the pole...the pole which had rotted off at the base and was teetering and held up solely by that fencing. It looked like a widow-maker to me so I finished the job.

Since codling moths fly at night and are most active in the warmer, early evening it seems probable that newly emerging bats would mop-up the flying insects closest to their home first. Hence bat habitats (or boxes or homes) in the orchard makes a lot of sense.

The attraction of the skirting-type habitat is that it closely mimics the natural habitat found under the loose bark of a dead tree. The bats can clock around the center of the habitat to find the temperatures they prefer. That is a big deal as the sun can turn a habitat into an oven.

A quick review of the literature suggests that having multiple habitats in the orchard will be to my advantage. The bats are likely to shift their preferences from mid-spring when it is cool and the dog-days of summer. Something as simple as painting the east side of the box a dark color and the west side of the box a light color (or covering with white corrugated metal with an small air-gap between the wall and the metal) can help reduce wild temperature swings.

Image from HERE.  This is a good picture of the bottom of a bat-box showing the dividers that create "crevices" within the box.

Some research suggests that offering a portfolio of boxes with different width openings or "crevice" dimensions will support the widest range of bat species. This is definitely NOT a one-size-fits-all proposition.

In general, larger bat-boxes provide more internal micro-climates which allows the individual bats to move around to find the conditions they prefer. A can of Crisco or lard might be a viable thermal-battery to buffer internal house temperatures. A wax that melts at 90F would be even better but accommodations must be made for the large change in volume.

The literature also suggests that maternal nesting requirements are more specific than general nesting boxes. That may be because the families are less mobile and cannot quickly shift to another house if a sunny day makes a box uninhabitable.

I expect I will be building and installing some bat-boxes within the next nine months.