Mammal Population Estimates

[james bennet]

Stumbled across this on the Defra website, and thought it might be of interest to WABers!

UK Defra | e-Digest Environment Statistics, Wildlife

(Table 7 is the best one to look at for an overview).

The biggest surprise for me was the population of common (brown or norwegian) rats. The number of 6,700,000 is far less than is commoly quoted (I constantly hear that they outnumber humans, when in fact this can only be said of the field vole), although the mammal society themselves admit it is hard to provide precise estimates.

The other surpise (to me) was the feral cat population, at 1,200,000. I can only assume these occur mostly in cities, but in any case this represents a massive carnivore population which shouldn't be here and which must be having some impact on our small mammals and birds (though I don't want to start that debate!). This being the case I'm surprised we don't hear more about it in the wildlife press.

Anyway, it made interesting reading and I'd be interested to hear what others make of the facts!

[wildliferescuer]

Makes very interesting reading with some surprising results, especially the feral cat population as you pointed out.

[Rob_D]

Also some info on the JNCC site Results of TMP Surveillance

Many mammals are much harder to survey than birds. I've participated in a few mammal surveys now, so I can appreciate the difficulty in getting a realistic estimate.

These may be the best estimates we have, but the margins of error might be very large - lots of them are category d or e. c means 50% error. d means broad ranking is correct. e means within an order of magnitude. You also have to consider when the survey data was taken. The rat estimate is from 1994 and is category d. The true value today could be (and probably is) much higher.

Wider Countryside Multi-Species Schemes

I think the feral cat data came from the National Gamebag Census. They send questionaires and the responders tell them how many predators they killed. They have tried to iron out the biases that are bound to occur in this survey. I'm not sure how they decided if a cat that was shot was feral or domestic? Perhaps any cat that is shot is always classed by the shooter as feral

[Ukwildlifeo]

Thanks for the links folks - very interesting