At the Western Plains Zoo recently, we had an out-of-hours tour where one stop was the Meerkats. I was fascinated to learn some of the more obscure things about them.
In a pack, there is a dominant female, and usually she is the breeding female but other females can also breed (it seems entirely dependent on the nature of the dominant female). Gestation is for 77 days and 2-5 pups are born.
Meerkats are a 'tribe' and have a territory to defend. They mark out their territory like other animals. Unlike other animals, they post a sentry at all times. The sentry scrambles to the highest point in their territory and keeps guard. They make calls to let the 'tribe' know how things are looking.
There may be more than one sentry at sometimes, but there is always one. Although, the keepers at the zoo said on rare occasions, they 'tribe' get so excited by food they may rush down to eat and then realise there is no sentry and one of the meerkats will scramble quickly into place. The keeper wasn't sure how the sentries were decided or if there was retribution for failure :)
Meerkats have a great sense of sight. At Dubbo Zoo, the sentry will call for birds flying past...but also for planes and some of those are quite high up and difficult to see.
As my memory is not the best, I checked most of the information here.