Wombats Moving Home

There comes a time in the life of many young mammals when they have to leave home. There are at least two major reasons for this. Firstly, any given place only has so many resources, so unless your parents die as soon as they've finished raising you (unusual among mammals, although not unheard of), at some point, you have to move elsewhere or there won't be enough food for both of you. Secondly, if the whole family stays together in one place, you'll never meet new sexual partners, forcing you to mate with your siblings - and we all know where that leads.

Understanding how and when animals disperse from their place of birth can be important for conservation as well as, on a broader scale, how new species and subspecies evolve and adapt. Nor is it necessarily something that only applies to young approaching maturity, since older animals may also choose to move from one place to another and often for similar reasons - competition or a lack of suitable mates. Whether a given animal chooses to move home, and how far they travel to do so, can be influenced by several different factors. 

When the Desert is Too Dry

The round-tailed ground squirrel lives
further east, and is not threatened

Many mammal species are territorial, carving out a patch of land for themselves which they then defend from same-sex members of their own species. Typically, they are less bothered about members of the opposite sex, for obvious reasons, and such territories will often overlap. Male territories tend to be larger than those defended by females, making it easier for them to meet as many females as possible. 

The size and relative location of such territories naturally vary between species, but also depend on the local conditions of terrain, climate and so on. The harder it is to find food, for instance, the larger your territory will need to be. As young animals grow up and leave home, they will need to find unoccupied territories to inhabit, or else somehow drive an existing resident out and take over. Males commonly travel further than females so that they don't end up with only their sisters or close cousins as potential mating partners, although there are a few species where it works the opposite way around.

Moving Away From Home

One common feature among many mammal species is that, once they become old enough to do so, they leave home to find a place to settle for themselves. Often, it's the young males that travel the furthest, and in animals that live in herds, colonies, or other groups, the females may not disperse at all, creating a matrilineal society - interestingly, the opposite is generally true in birds. This discrepancy between the sexes ensures that when the males do find somewhere to settle down, the females that will become their new neighbours or pack-mates will not also be their own sisters and other close relatives.

But there are other reasons why animals might choose to disperse, sometimes moving from one location to another once they are already adult. This may be due to some sudden disruption in their original habitat, or to longer-term effects, such as climate change. Either way, while it's not an easy subject to study in the wild, understanding the causes and practices of animal dispersal can be important for issues such as conservation and understanding wider population dynamics. 

Jackals on the Motorway

Mammals tend to have a particular area in which they live most of their lives and conduct their various activities. This is known as the animal's "home range", and it's not quite the same thing as a "territory". That's because the latter is an actively defended bit of land, that the animal strives to keep clear of rivals, perhaps marking it with scent as a warning, and using aggression against intruders if they have to. The majority of mammal species don't bother to defend territories, but that doesn't mean that they don't have a home range - after all, they have to live somewhere.

One key difference between a territory and a home range is that the former, by definition, is not shared with any neighbours. Of course, the animal might be social, living in herds, packs or other kinds of band, so that all members of the group share a single territory, but, again, it's not shared with outsiders. A home range, on the other hand, almost always overlaps with at least some others used by members of the same species, especially if they happen to be of the opposite sex. Breeding would be problematic if they didn't.

Should I Stay or Should I Go?

Although they are hardly alone in this, mammals are noted for their care of their offspring. Yet many of them are solitary animals, and the young leave home as soon as they are able to survive on their own, so that the only groups seen are when a mother is caring for her children. But, of course, many mammals live in herds, packs, or other groups, with at least some individuals staying with their parents once they grow up.

But, even in herds, some animals do leave home, to establish or join new groups elsewhere. How do they make this decision as to whether to leave or stay? For many, its a fairly simple rule: the males leave, and the females don't. That means that a herd or other group is dominated by a core of females descended from a single matriarch, while the males have generally come in from outside. Initially, in most cases, the males wander about looking for a new group, perhaps together with one or two other young males in a similar situation, until they eventually find someone that will take them in. This ensures that they don't end up mating with their own female relatives, and keeps the gene pool as wide as possible.