I  often like to watch Dog Whisperer, and am fascianated by how a very small dog can often dominate a much larger one, simply through being of higher “energy”, as Cesar Millan calls it.  Watchers of that programme can see that this works across species too, as Cesar trains owners not to let their dogs dominate them, but to take over as human “pack leader”.  Now comes an interesting example of this working between related rodent species.

is a city of over 1 million people, about 76 miles north of Delhi.  And they have a problem with rats.  Perhaps not as severe as that faced by the people of Hamelin in medieval times[1]:
They fought the dogs and killed the cats,
And bit the babies in the cradles,
And ate the cheeses out of the vats,
And licked the soup from the cooks’ own ladles!  [2]
But they were certainly a problem to the police, chewing up vital papers and gunny bags.  About a month ago, someone suggested introducing domesticated white mice, which they went and purchased from a laboratory supplier.

Within a month, the black rats had disappeared, and now they are planning to introduce white mice to other police stations in the area.

A local zoologist said that the white mice have genetically more dominant traits than the black ones and eventually they come out on top in the competition.

In Britain and other chilly countries, the Black Rat (Rattus rattus), which carried the bubonic plague, has been largely driven out by the Brown Rat (Rattus norvegicus), which doesn’t.  For this reason, my father used to refer to the latter as “The Gentleman who Saved Europe”.

And Hamelin again has a rat problem.

source: Times of India

[1] http://en.wikipedia.org/wiki/Pied_Piper
[2] The Pied Piper of Hamelin by Robert Browning.