San Ramon family has 2 houses ready for occupancy; bats only, please

DEAR JOAN: A few years ago we were having bats nest in the top of the columns of our protected front porch. The only way we could get rid of them was to insert cardboard into the spaces after they had flown out for the evening.

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We bought two cedar bat boxes and mounted them to the end of the front and back fences on wooden poles about 10 feet high. We haven’t gotten any visitors to the bat houses. Is there something else we could do to encourage bats to use the bat houses?

— Laura, San Ramon

DEAR LAURA: It’s funny how we can attract bats to places we don’t want them to be, yet strike out when it comes to attracting them to places we do want them.

It’s still a matter of luck, but you can improve your chances by making sure you’re meeting all the requirements these marvelous winged mammals seem to have.

The first is to install a bat house 12-20 feet above ground — 15 feet seems to be a sweet spot. Your bat box might be a little too low.

The box should also be in a sunny location, but away from bright lights at night. Bats need water, so bat boxes located within a quarter mile from a river, stream or pond have a better chance of attracting bats to their new home.

Bats also need a clear flying zone to and from their houses, so trim back shrubs, limbs and foliage that would block or restrict a bat’s movements, clearing a 15- to 20-foot diameter around the box.

Bats might be creatures of the night, but they require the warmth of the sun to keep their house heated. The location for the box should get 6 to 8 hours of sun, and the entrance should face west, south or southwest.

Growing night-blooming plants near the bat box also is a good idea. The blooms will attract insects, which will attract bats.

It can take some time for the bats to find the boxes and decide it’s a good idea, although some are never occupied. Do the best you can and be patient because loss of habitat means a lot of bats need safe homes. Now is a good time of the year to erect a bat box. If you put up more than one, place them back-to-back with a ¾-inch gap, or put them in the same area but at different heights.

DEAR JOAN: A nocturnal pest eats grapes and leaves the skins behind. Often there is a neat pile of skins where the grapes were eaten. The vines are enclosed in chicken wire to no avail. Do you have any suggestions for next year?

— Weldon Wong, Atherton

DEAR WELDON: If you’re certain the damage occurs during nighttime hours, the most likely culprit is rats. That’s classic rat behavior.

Birds also are fairly adept at plucking out the sweet pulp and leaving the skins behind, but they operate during daylight hours.

Next year, improve your barrier. Chicken wire is no deterrent to rats. You need something more substantial, such hardware cloth, which is a metal mesh with smaller holes and stronger wire.

The Animal Life column runs on Mondays. Contact Joan Morris at [email protected].