Special behavioral features of the dromedary include snapping at others without biting them and showing displeasure by stamping their feet. They are generally non-aggressive, with the exception of rutting males. They appear to remember their homes; females, in particular, remember the places they first gave birth or suckled their offspring. Males become aggressive in the mating season, and sometimes wrestle. A 1980 study showed androgen levels in males influences their behavior. Between January and April when these levels are high during the rut, they become difficult to manage, blow out the palate from the mouth, vocalize and throw urine over their backs. Camels scratch parts of their bodies with their legs or with their lower incisors. They may also rub against tree bark and roll in the sand.