Bamboo flowering: kicking rat reproduction into ‘overdrive’
July 26 - August 1, 2010
THE relationship between plagues of rats and bamboo flowering was the focus of a workshop held in Mizoram, northeastern India, in May 2009.
At the workshop, Dr F Lalnunmawia, an assistant professor at Mizoram University’s Department of Forestry, said that rodent outbreaks similar to the one that occurred in Bago and Daik U are recorded at roughly 48-year intervals in Mizoram: 1815, 1863, 1911 and 1958. This corresponds with the flowering of local bamboo plants.
Using this data, he said the university was able to accurately predict a population boom in 2007.
“It is a common belief that the bamboo flowering gives a big boost to the rat population, though a proper scientific explanation is meagre,” Dr Lalnunmawia said in his presentation.
In 2007, torrents of rats affected both Mizoram and Paletwa township in Chin State. Paletwa township and neighbouring Kyauktaw township in Rakhine State experienced further rodent outbreaks in 2009.
Daw Nyo Me Htwe, a rodent ecology doctorate student at the International Rice Research Institute, studied the impact of the Paletwa outbreak.
In an article by Filipino author Trina Leah Mendoza on the IRRI website, Daw Nyo Me Htwe said the rats in the Platwa incidents were of the Rattus rattus species and that the outbreak began two months after the bamboo flowered in 2007.
Scientists have two theories as to why bamboo flowering could lead to plagues of rats.
The first suggests that the bamboo seeds “supercharge” the reproductive capacity of rats.
“It is … claimed that the bamboo seeds, which are favourites of the rodents, increase their fertility to such an extent that the number of their litter jumps from the normal 6-8 to 12-18,” Dr Lalnunmawia said.
But he added that a chemical analysis of bamboo seeds showed that their nutrient content was not particularly different from other food sources, such as rice, wheat and millet. Instead, Dr Lalnunmawia proposes that the abundance of food caused by the flowering eliminates the need for rodents to devour their offspring, resulting in an explosion in the rat population.
“In normal times, the bamboo forest has very little food for rats to eat, so mother black rats reproduce infrequently,” he said.
“If food is especially short, rats are more aggressive and conveniently eat their young. … The bamboo fruit that appears every 48 years radically changes that equilibrium with the result that cannibalism disappears and rat reproduction kicks into overdrive. Over several months of bamboo fruiting, a single well-fed female can start a cycle resulting in nearly 200 offspring.”
The lifespan of rats found in these forests is about two years, and they can reproduce from six weeks of age. Since bamboo flowering can last for six months, massive generations of rats can arise.
But as the seeds are consumed and the rats face overpopulation, they migrate to areas of human settlement in search of food.
