Moss' focus is on behaviour and social structure, especially mating systems and breeding. The radically different mating and territorial systems of antelope species, for example, are linked to their ecological niches.
"When a herd of [female impala] comes into a male's territory, he tries to keep them there by various strategies, mainly herding. He also uses one amusing method in which he "pretends" that he has seen some danger over in the next territory and stands in an alarm posture in the hopes of persuading the females not to move on. He tests the females for estrus by sniffing the vulva or by collecting some urine and then performing Flehmen. If there is a female in estrus, the male will begin to herd her more intently. With the estrus female in his territory, the male does not have to worry about competition from other males. He will normally be left alone to mate with her, as he has complete dominance in his own territory."
There's also some information about conservation, poaching, and human attitudes to different species: baboons as "born criminals", for examples, or the changing sentiment towards lions.
"The early hunters and settlers in Africa considered the lion vermin, without the dignity of a game animal. Lions were simply shot on sight. Their reputation deteriorated even further when they became famous for man eating... During the 1920s and 1930s their status was raised somewhat, as they became suitable ferocious prey to be stalked by intrepid white hunters."
Moss also includes a bit about the researchers who carried out the studies she summarises, and the observational methodologies involved.
There's almost no quantitative data in Portraits, let alone any formal life-cycle theory or ecology — there's not a single diagram, table or figure. (There is, however, a nice if grainy selection of black and white halftones.) The presentation is discursive and approachable, with something of the feel of a wildlife documentary.
Portraits in the Wild was first written in 1975 and revised in 1982, so it is based on research from the 60s and 70s (for some species the first serious studies of behaviour) and is obviously dated. No more recent treatment of this kind exists, however, so it's still useful background reading for visitors to Africa. (A better choice for field use would be a book like Richard Estes' The Safari Companion: A Guide to Watching African Mammals, which has a similar focus on behaviour and social structure but covers many more species and is structured as a guide.)