The challenge for bat house builders is to provide a range of temperatures adequate to meet bat needs despite external changes that occur throughout an average day. An ideal house would offer the widest possible temperature range, and that is what we have attempted to provide in the new designs. Little brown bats are much more tolerant of heat than big brown bats and have been recorded rearing young in temperatures as high as 104 degrees, though they prefer 80 to 90 degrees. Big brown bats, however, are known to abandon roosts when the temperature rises above 95 degrees. Placing several dark and light-colored houses close together to absorb differing amounts of solar heat can greatly expand the available temperature options and may be especially advantageous when attempting to attract nursery colonies.
Bachelors tend to selct the cooler temperatures year-round.
Where you mount your bat house also plays a major role in its internal temperature. In cool climates houses on poles can better take advantage of exposure to the sun. Try white and light or medium-brown houses similarly oriented in warmer regions. The darker house would be warmed early in the morning, remaining quite warm through the day. The northwestern house would be mostly shaded until afternoon and then absorb minimal heat due to its light color.