Monday, 5 November 2012

Making a living alongside humans

Stillness descends over the town’s margins in the hour before dusk. The paths down by the river fall quiet and no longer echo to the hollow ring of footsteps or the chatter of young voices. This is one of my favourite times of the day and one that delivers a sense of transition, not just from day to night but also from the human-dominated landscape to a more natural one. This is the time when the ducks, Canada geese and swans begin to settle and the rats emerge. All along the footpath, but particularly in those stretches where we humans sit to eat our lunch, the rats can be seen foraging and scavenging. Some seem wary but others, perhaps those that are old hands at making a living alongside people, allow a closer approach.

Rats have a bad press, a legacy perhaps of earlier times when they competed for our food and were associated with the spread of devastating disease. Despite this, I have a soft spot for them and I admire their adaptability, tenacity and success. These are common rats. Although sometimes known as brown rats, their colour is variable and some individuals are very dark, almost black, prompting confusion with the very much rarer black rat, a species now confined to a few isolated and often transient populations within Britain. The common rat is thought to have originated in the vast steppes of central Asia, spreading west across Europe via trade routes and reaching Britain in the early 1700s. Once here, the species spread rapidly, displacing its smaller relative and occupying just about any habitat where natural foods were augmented by those associated with human activity.

Rat society is somewhat more complex than you might at first imagine. Common rats tend to live in colonies, loosely structured affairs that appear to be comprised of small groups, known as clans. Each clan usually comprises of a male or a pair, together with a harem of other individuals. The clan maintains a territory based around a burrow system and one or more food resources. Territory size decreases as the density of rats within a population increases and this leads to a clear dominance hierarchy. Those individuals towards the top of the hierarchy gain greater access to food resources.

The spread of sizes among the individuals that I see by the river indicates a thriving colony and, most likely, one that has had a good year. Breeding takes place throughout the year, the young females sexually mature at just eleven weeks of age, so it is easy to see how this colony has been able to develop and to take the opportunities afforded by our wasteful practices and grubby habits.

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