Should I use treated wood or paint on a nest box?
There are no conclusive studies that determine whether residual fumes from paint or pressure treatment can harm the birds. In the absence of evidence, we recommend using untreated, unpainted wood to construct boxes (cedar, white pine, and yellow pine are good rot-resistant choices). Pressure-treated wood has been impregnated with a combination of pesticide and fungicide, and therefore, should be avoided as a nest box material; instead, you can extend the life of your nest box by gluing all the joints before nailing them.
In hot climates, where daytime temperatures regularly exceed 95 °F, some nest box monitors choose to paint the exterior of boxes so that they stay cooler. Proper ventilation and a roof that extends two inches over the sides will help shade the box and protect it from the elements, reducing the need for paint. However, some additional cooling may be gained by painting the roof and exterior walls a light color (white is preferred for Purple Martin houses, but opt for tan, gray, or dull green for other cavity-nesting species as these are less conspicuous to predators). If paint is deemed necessary by the monitor, then it should only be applied to the exterior. Even zero- and low-VOC latex paint formulas can release fumes for months or even years, so if you paint, plan to do so in the fall, which will give fumes plenty of time to dissipate throughout the winter.