Bats and Bat Houses
Introductory Discussion
Bats
Bats are small, flying mammals from the order Chiroptera. Of the 25 species found in California, almost all are insectivores
that feed on vast numbers of night-flying insects, making them an important part of the ecological community.
Of the 25 species found in California, Several of these species—pallid bat (Antrozous pallidus), big brown bat (Eptesicus fuscus),
Yuma myotis bat (Myotis yumanensis) and other Myotis species, and Mexican free-tailed bat (Tadarida brasiliensis)—frequently
use man-made structures such as attics, barns, or bat boxes for roosting sites
and are the species you most likely will find in urban areas.
Bat Houses
If you chose to put up a bat house, make sure it is in an area that has minimal disturbance from people and animals. Sometimes
sick bats fall out of the roost where children and household pets easily can pick them up.
Bat houses attached to the sides of buildings tend to have good success, but, not only is the usual intent of erecting a bat house
to get bats away from buildings, but bat droppings will accumulate below creating a hazard.
Bat houses on poles in open areas may work best. In fact, many reports demonstrate that two houses, back to back, mounted on
an 12’-14’ pole are optimal, likely due, in part, to the need for early morning warmth and late afternoon cool. Bats rarely occupy
houses placed in trees. Installing bat houses before March improves the chance of occupancy. It is not unusual for bat houses to
remain unoccupied for a year or more. Bats prefer houses that are within 1/4 mile of water with enough room to drink on the wing.
Use patterns
In one study, among the eight largest samples reported by individual people who had erected multiple bat houses, use rates varied
from 0 to 96%. For example, at one Oregon location, none of 18 houses placed on trees in dense forest were occupied, while 23
of 24 at another Oregon site attracted bats when placed both outside and inside a barn and on poles at the edge of woodlots. The
only one not used was mounted on a shaded tree trunk.
Time until first occupancy
It has long been believed that bat houses were most likely to be occupied after at least one or two seasons had passed, but this study
found exactly the opposite. Most houses used by bats were occupied in the first season. Eighty-five percent were first used within two
seasons and only 15% in the third through sixth seasons.
Introductory Discussion
Bats
Bats are small, flying mammals from the order Chiroptera. Of the 25 species found in California, almost all are insectivores
that feed on vast numbers of night-flying insects, making them an important part of the ecological community.
Of the 25 species found in California, Several of these species—pallid bat (Antrozous pallidus), big brown bat (Eptesicus fuscus),
Yuma myotis bat (Myotis yumanensis) and other Myotis species, and Mexican free-tailed bat (Tadarida brasiliensis)—frequently
use man-made structures such as attics, barns, or bat boxes for roosting sites
and are the species you most likely will find in urban areas.
Bat Houses
If you chose to put up a bat house, make sure it is in an area that has minimal disturbance from people and animals. Sometimes
sick bats fall out of the roost where children and household pets easily can pick them up.
Bat houses attached to the sides of buildings tend to have good success, but, not only is the usual intent of erecting a bat house
to get bats away from buildings, but bat droppings will accumulate below creating a hazard.
Bat houses on poles in open areas may work best. In fact, many reports demonstrate that two houses, back to back, mounted on
an 12’-14’ pole are optimal, likely due, in part, to the need for early morning warmth and late afternoon cool. Bats rarely occupy
houses placed in trees. Installing bat houses before March improves the chance of occupancy. It is not unusual for bat houses to
remain unoccupied for a year or more. Bats prefer houses that are within 1/4 mile of water with enough room to drink on the wing.
Use patterns
In one study, among the eight largest samples reported by individual people who had erected multiple bat houses, use rates varied
from 0 to 96%. For example, at one Oregon location, none of 18 houses placed on trees in dense forest were occupied, while 23
of 24 at another Oregon site attracted bats when placed both outside and inside a barn and on poles at the edge of woodlots. The
only one not used was mounted on a shaded tree trunk.
Time until first occupancy
It has long been believed that bat houses were most likely to be occupied after at least one or two seasons had passed, but this study
found exactly the opposite. Most houses used by bats were occupied in the first season. Eighty-five percent were first used within two
seasons and only 15% in the third through sixth seasons.