Ardrey's book was one of the first to really popularize concepts of animal territoriality. As such, he does an excellent job, in fact, possibly too good. For a time, after the publication of this very popular scientific book, concepts of territoriality became something of a scientific and even nonscientific rage. This is a little unfortunate, because in mass popularization, something is usually lost.
Nevertheless, there can be no question that animal territories are important throughout nature. Most of us have no problem with identifying territoriality in, let's say, a marsh wren as it sings out its warning and fights off intruders. It is sometimes a little more difficult to see territorial impulses in oneself, but they are surely there. All of us require a certain personal space and, at larger levels, we require the space of a home, state and a country. Many wars are precisely over territory.
Still difficult to recognize, is the territoriality of flock and herd animals but, even in these situations, territory is everything. A bird in a flock requires personal space. If another bird intrudes on it, he will be pecked and, if he doesn't get out of the way, killed. It starts as early as the nest or den when infant animals pound on one another to assure themselves more space and more food.
Ron Braithwaite author of novels--"Skull Rack" and "Hummingbird God"--on the Conquest of Mexico