Rat observations are increasing in New York
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It has long been predicted that Many species of pests will thrive as the planet warms up – and now a study of 16 major cities has found that rats populations increase the fastest in areas where Average temperatures increase the fastest.
It is extremely difficult to estimate the number of rats in a city, so Jonathan Richardson At the University of Richmond in Virginia and his colleagues did not try this. Instead, they have an idea of how populations change by examining the number of complaints concerning rats recorded by cities.
In the United States, this information is often accessible to the public and the team has also been able to obtain data for some places outside the United States by contacting city officials. Researchers only understood cities in their study if at least seven years of data were available and that the collection methods had not changed. This left them data for 13 American cities, as well as Tokyo, Amsterdam and Toronto.
Their analysis suggests that the number of rats decreases in New Orleans, Louisville in Kentucky and Tokyo, is stable in Dallas and St Louis, and increases in the other 11 cities, with the fastest growth of Washington DC, San Francisco, Toronto, New York and Amsterdam.
Richardson and his colleagues then examined several factors that could explain trends. They found that the strongest link was with the average temperature increase During the last century. The next strongest link was urbanization, evaluated from satellite photos, followed by the density of the human population. The city's GDP has not shown a link with rats trends.
It is known that in the colder cities, the number of rats falls during the winter and the peak in summer, it is therefore logical that growing temperatures lead to an increase in populations, say the researchers. More rats mean a greater risk than people get diseases transmitted by rats, such as leptospirosis, also called Weil's disease.
The results show that cities must do more to control rats as the planet warms up, and the cutting of their food supply is the most important measure, explains Richardson.
“Securing food waste and making it inaccessible to rats is the approach that will have the greatest impact on rats control,” he said. “We see a New York pilot in certain districts – finally – and that puts a measurable breach in number of rats.”
