This refers to the number of male and female animals - the first number is the number of males, the second females, and sometimes there's a third for animals of unknown sex.
So 1.1 is one male and one female, 1.2 is one male, two females.
(If there's just one male, it would be 1.0. A pair and their as-yet-unsexed twin offspring would be 1.1.2 - it's a neat way to summarise the animals the zoo has).