The calls of ruffed lemurs vary only slightly between the two species. In fact, in captivity, it has been documented that red ruffed lemurs understand and even join in the alarm calls of black-and-white ruffed lemurs. One minor difference between the vocal repertoires of these two species is in the pulse rate and frequency of the "pulsed squawk", which is much faster and higher in red ruffed lemurs than in black-and-white ruffed lemurs. The difference in this vocalization is only interspecific, showing no signs of significant sexual dimorphism within each species.