Tools of the project: BCM bat boxes, internal baffles with attached temperature data loggers, and the "loose" logger for recording ambient temperatures.

BCM is the only bat box manufacturer to offer bat boxes finished with several coats of paint. Generally, decorative bat boxes found in most nature shops and garden centers do not attract large maternity colonies of bats. Some outdated instructions which come with these boxes advise against painting the box. [see Why Other Boxes Fail] Keep in mind that little browns seek roosts that routinely peak at 100° F. To find the difference bat box color makes in the cool northern United States, we started with BCM's successful Three Chamber Box assembled off the shelf. We also took a nearly completed Three Chamber Box, assembled but unpainted. Both boxes have sealant along all seams, and the internal baffles installed. Using these two boxes as a base, we then affixed different combinations of roofing material for four different experiments.

We placed a Hobo data logger in each bat box, taped about one inch from the top of the second baffle. The baffles were installed in the same manner. The data loggers were set to record one sample every ten minutes. The graphs represent daytime temperature curves around June 1, 1999. The test locality was Harrisburg, Pennsylvania. Note that these graphs merely shows comparison of bat box colors, it does not necessarily show optimum internal box temperatures.

We have presented a portion of the resulting graph #1 on this page. From this we can determine the following:

• The black box heats up a few degrees faster in the morning.
• The black box averages about five degrees warmer during midday.
• Both boxes retain the same amount of heat in the evening, to be expected.
• The black box averages ten degrees warmer than the outside temperature during midday.

Due to how particular bats are, bat boxes in the northern United States should be painted or stained dark brown or black to ensure maximum solar heating during critical Spring mornings.

This comparison suggests that by adding a white roof to the unpainted box, the interior temperature drops about five degrees. Sound insignificant? It could be the difference between ten bats occupying the box and 100. The significant drop in temperatures around 15:00 represent thunderstorm activity. The sudden rise in the ambient temperature around 18:30 is because that logger was moved inside out of the rain. Despite the constant rainfall, the black box with black roof retained slightly more heat than the plain counterpart.

This graph shows only about a three degree difference when comparing roof color on black boxes. This is to be expected as the roof only accounts for about 25% of the area exposed to solar heating.