|Summary: Mother-pup communication is important in gregarious species such as Galápagos sea lion, especially since mothers nurse only their own pup. In order to identify the mother from the group of females returning from the daily foraging trips, Galápagos sea lion pups learn to recognize mothers calls after approximately ten days from their birth. Recognition ability becomes even more important since newborns have to compete with older siblings yearlings that continue suckling even after the birth of the newborn. Mother-pup communication is consistent of vocal and olfactory cues. Firstly there are long distance calls and after approaching each other mother reassures with sniffing if the pup is hers. Human presence can influence mother-pup communication in several ways. It can cause animals to flee or perform agnostic behaviour, and hence increase their energy budget and prolongs mother search, thus decreasing feeding success. On the other hand in habituated colonies humans induced noise aggravates long distance communication. In order to evaluate a possible impact of human presence on a breeding colony, observations of mother-pup communication in two colonies on Galápagos Islands were performed. Observations of mother-pup communication in Galápagos sea lion pups and yearlings were performed during the warm season 2010 on two locations on San Cristóbal, Galápagos: Playa de los Marinos, located in the centre of the town Puerto Baquerizo Moreno, and La Loberia, approx. 2 km out of town. To choose the most appropriate time for observations, two daily counts of pups behaviours were performed. Results showed Galápagos sea lion pups have two activity peaks: the early morning and the late afternoon activity peak. These were the times when suckling and searching for a mother was most frequent. Therefore measurements of the time spent searching for the mother and counts of number of non-kin adults checked during the search were performed in late afternoon. Human presence was recorded as a number of people present at the observed colony during the observation. In total 21 pups from La Loberia and 59 pups and 26 yearlings from Playa de los Marinos were observed. Pups from Playa de los Marinos showed higher searching effort by performing significantly longer searches with significantly higher number of non-kin adults checked than both, La Loberia pups and yearlings from Playa de los Marinos. On the other hand yearlings were more successful in suckling (23.1 %) than pups. There was no correlation within suckling success and human presence/interaction, and human presence does not prolong search behaviour of yearlings and pups. Conclusions of the human impact cannot be performed also due to different size of the observed colonies. But results from the three observations from La Loberia, where number of visitors in direct vicinity of each individual pup was counted, indicate that human impact does alter sea lion behaviour and causes earlier termination of search behaviour without successful ending.