Those big ears are not just there for show. Namibian elephants detect rainstorms at a distance of as much as 280km away, and will travel towards them in search of fresh water and the growth that comes after rain. Sound appears to be the most likely, although still unconfirmed, mechanism.
This is more than the distance from the center of New York to Baltimore, or London to Manchester - although in either case the noises of industrial life might confuse an immigrant elephant's senses.
Namibia's elephants were almost wiped out by poachers in the 1970s and 80s, but have started to recover since wars in the region stopped, allowing the government to provide some protection.
African elephants have adapted to a diverse range of climates, but the Namibian environment is a strain. The country is the driest in sub-Saharan Africa so it is important to make the best use of what rains do come. Elephants in drier regions have been found to have the largest ranges, up to 14,000km2, with the longest journeys during the wet season.
The Namibian rainy season, such as it is, runs from January to March and it has been noticed that during this period the local elephants can suddenly shift their direction of migration, with no apparent reason.
A team led by Emeritus Professor Michael Garstang of the University of Virginia placed GPS trackers on elephants from 14 herds between 2002 and 2009. In PloS One they compare the movements of those whose collars worked continuously with satellite rainfall data and found the elephants were turning towards storms astonishing distances away. Sometimes several widely dispersed herds all began converging on a storm simultaneously.
The researchers admit they cannot be certain how the elephants know where the rain is, but argue, “Rain-system generated infrasound, which can travel such distances and be detected by elephants, is a possible trigger for such changes in movement.” Whether the sound would be from thunder, or drumming on the ground, they're not sure.
Elephants use infrasound, frequencies too low to be audible to humans, to communicate over large distances, and studies of their hearing and pressure waves from thunderstorms suggest they should be able to pick up the noises at least 100km away. However, these left open whether the elephants can tell where the sound is coming from, even if they can identify that it is happening.
Puzzlingly, while the elephants sometimes changed direction to head towards rain the day it fell, some took as much as 20 days to plot a new course. In other cases the elephants changed path 7-12 days before the rain, as if they had some forewarning of where they should be heading, but seemed to pick the direction with uncanny accuracy.
Garstang has previously collected evidence that elephants responded to the 2004 Indian Ocean tsunami well before it struck.
