The marks are much closer together near the boundaries of a pack's territory. A wolf will also mark the same scent post over and over again near the boundaries of its territory. Wolves will chase out foreign wolves that enter their territory. If the intruders aren't fast enough, they may be attacked or killed and occasionally, a large pack will drive a small pack out of its territory. This releases odours from the glands in the wolf's paws.
Wolves also howl to warn other wolf packs that they have entered foreign territory.
Wolves will often answer the howls of another wolf pack. However, wolves will remain quiet if there are pups present so they don't attract attention to the pup's whereabouts. Wolf pups are vulnerable to attacks from large predators, such as bears or mountain lions.