Chimpanzee age impacts the frequency of alarm signalling. Chimpanzees over 80 months of age are more likely to produce an alarm call than those less than 80 months of age. There are several hypotheses for this lack of alarm calling in infants zero to four years of age. The first hypothesis is a lack of motivation to produce alarm calls because of mothers in close proximity that minimize the infants perception of a threat or that respond to a threat before the infant can. Infants may also be more likely to use distress calls to catch their mothers attention in order for her to produce an alarm call. Infants might also lack the physical ability to produce alarm calls or lack the necessary experience to classify unfamiliar objects as dangerous and worthy of an alarm signal. Therefore, alarm calling may require advanced levels of development, perception, categorization, and social cognition.