Wolves have an extraordinary sense of smell, in the right wind, they can detect a moose at more than 2 kilometres (1½ miles) and they probably obtain a great deal of information from their scent marks. They may even use them to find their territories, on which locations such as kill sites and trail junctions are registered. Thus it is probably significant that the crossroads of trails-the decision points for efficent route-finding are generously scent-marked, making them vivid and memorable.
Because our own sense of smell is weak, we are at a loss to properly decode these olfactory messages, but it seems possible that wolves pick up more personal details as well: which individuals, of which sex, were last here; who is travelling with whom; and how long it has been since the area was hunted. At the very least, it is clear that they can distinguished between fresh marks and old ones, and can tell when they pick up a stranger's scent. Wolves seem to scent-mark more frequently near the edges than in the centre of their territories, perhaps because they can detect the scent of their neighbours in the borderlands. There is often a narrow band of overlap, about a kilometre wide, which adjacent packs explore at different times. The foreign odours apparently stimulate the animals to leave their mark on the disputed zone and then to turn around and head for the safety of their own ground.
Assuming that they are relatively well fed, wolves sometimes choose to give up a meal rather than risk trespassing on another pack's land. Biologists working in the northeastern Minnesota tel the story of a pack that had chased and wounded a deer. The prey was badly hurt, yet on it ran, with the wolves on its heels. But when it crossed a river that served as the dividing line between two territories, the wolves followed for a short distance, then stopped, scent-marked and trotted back home. The next day, the neighbouring pack killed and ate the deer.