Recent Rat population numbers over-inflated says expert
Added: (Fri Oct 31 2008)
Pressbox (Press Release) -
Recent Press reports of the UK rat population exceeding the human population are likely to be gross over-estimates says London expert Dr David Channon.
He says the more reliable estimates centre on the figure of about 25 Million give or take a few million.
The 60 Million figure often quoted comes he says from a estimate made at the turn of the last century which related rat numbers to cultivated acreage and coincidently, human population.
At that time there were 20 Million acres in cultivation and an estimate was made of one rat per acre. The human population around 1900 was about 20 Million as well which lead to the rough link of one rat per person.
However Dr Channon points out that the driver for the link was acreage in cultivation and not human numbers. So, whilst the human population is now around the 60 Million mark, the cultivated acreage is not markedly different to what it was a hundred years ago.
Despite this, the one rat per person link has now achieved the status of an urban myth.
What may be driving reported sightings is the string of wet summers he says. Rats are commonly found by water courses and flooding over the past three years may have pushed them from these locations to drier areas inland where they have come into more contact with people.
In agricultural areas he thinks rats may have struggled this year since cereal crops have been poor as a result of the wet August.
In urban areas, the switch to fortnightly bin collections may well have provided them with increased food opportunities.
People don’t want to live alongside decaying food for two weeks and often put it out in the garden where opportunist pests like rats, pigeons and foxes can clean it up. This creates risks both for the householder and the neighbours.
Dr Channon suggests that it is better not to put out cooked food at all since the pests, once attracted will create other problems and pose a serious health risk.
Green waste can be composted directly. Kitchen trimmings and some cooked vegetables can be put through a wormery. Cooked food waste can be put through a Bokashi digester and then through a wormery. These are environmentally friendly solutions to waste food and smell but they do take a bit of effort and discipline to manage safely.
Dr Channon and a team of scientists from Microbee Limited a London based pest control company have been monitoring London’s sewer rat populations for approaching the last 25 years, reporting to Thames Water and say that the numbers are nowhere near as high as people fear. London’s sewer network was originally developed for a much smaller population covering a much smaller area. It has been stretched by urban sprawl and now struggles to cope in heavy rainstorms. “Every time we get a major rainstorm, the sewers fill right up and any rats in them that cannot escape get drowned” says Dr. Channon. This means that rats entering the sewers to live and breed have to start up all over again after each flood. Since the number of severe rainfall events appear to be on the increase, he is not expecting sewer rat populations to increase markedly in the near future.
Microbee Limited 0208 540 9968
Rat publications by the Microbee team:
Channon D., Cole, M., Cole L. (2000). A long-term study of Rattus norvegicus in the London Borough of Enfield using baiting returns as an indicator of sewer population levels. Epidemiology and Infection, 125: 441-445.
Channon D., Tsyganov A.(2001) Responses of Sewer Rats to Rodent Bait. International Pest Control July/August 2001 160-164
Channon D., Roberts T. & Verity J. (2002) Rats and Interceptors, A study of sewer rat’s (R norvegicus) behaviours when encountering this feature of sewerage engineering International Pest Control July/Aug.
Channon D., Cook N., Hook H., Knowles L. (2004) Preferred Locations in Sewers; a covert study of Rattus norvegicus behaviour. International Pest Control July/Aug 2004 46, 4 194-8
Channon, D, Murfitt E. (2005). UK Rat myths explored International Pest Control, vol 47, 4 July/Aug 2005 192-4
Channon, D., Channon, E., Roberts, T., Haines, R. (2006) Hotspots: Are some areas of sewer network prone to reinfestation by Rats (Rattus norvegicus) year after year? Epidemiology & Infection 2006: 134, 41-48
Channon, D., Chen-Hussey, V., Gawne, J. (2006) A study of data collected during rat baiting in the sewers of three London boroughs International Pest Control vol 48, 5 September/October 2006 250-256