Short answer: temperature fluctuations. Wood is a natural material, and thus will suffer under the effects of extreme heat and cold. Due to this, wooden piccolo players are always advised to never leave their instruments in areas where there are temperature extremes. If you have a wooden piccolo it is absolutely critical to keep your wooden piccolo at room temperature, which is around 18 to 20 degrees celsius. Anything far below or above means that the wood is going to expand, contract, and suffer from cracking. In addition to maintaining the correct temperature we recommend always storing your piccolo in a dedicated case.