An international team of researchers has found the first evidence of a non-human species cultivating plants for use other than as food.
Published today in the journal Current Biology, the new study reveals that male Spotted bowerbirds, Ptilonorhynchus maculata, have unusually high numbers of fruit-bearing plants growing around their bowers and use these fruits in order to attract females.
The team does not believe the bowerbirds are intentionally cultivating the plants: it is more likely that they are growing around their bowers as a result of the birds gathering fruits for display.
“Until now, humans have been the only species known to cultivate plants for uses other than food,” said Dr. Joah Madden of the University of Exeter, a lead author of the study. “We grow plants for all kinds of things – from drugs, to clothing, to props that we use in our sexual displays such as roses – but it seems we are not unique in this respect.”
Bowerbirds are well known for their unique courtship behavior, which involves males building ornate bowers. Males gather brightly-colored objects to decorate their bowers, in order to attract females.
The team observed bowerbirds in Taunton National Park, Central Queensland, Australia, and found higher numbers of potato bush plants, Solanum ellipticum, around bowers than in other locations. These plants have bright purple flowers and green fruit.
The researchers found that the birds were not selecting locations with a high number of the plants, but rather that they were growing plants around their bowers.
Bowers with many fruit on them are especially attractive to choosy females. Males collect the fruits, but when the fruits shrivel, they discard them nearby. This results in seeds germinating in the ground around the bower. Bowerbirds clear the area around their bower of grass and weeds, making ideal conditions for new plants to germinate. Male bowerbirds can maintain a bower in the same location for up to ten years, so will benefit from establishing plants that may survive for several years.
The team found that, like farmers selecting for fatter pigs or larger seeds, the bird’s behavior may lead to a change in the appearance of fruits. The fruits from plants close to the bowers were slightly greener in color than those found on other plants. The researchers tested the males’ choices and found they preferred this color to that of the other fruit.
“We do not believe bowerbirds are intentionally growing these plants, but this accumulation of preferred objects close to a site of habitation is arguably the way any cultivation begins,” Dr. Madden said. “It will be very interesting to see how this mutually-beneficial relationship between bowerbirds and these plants develops.”