An endangered Tasmanian songbird doesn鈥檛 have to wait for manna from heaven: it goes out and gathers its own.
The forty-spotted pardalote (Pardalotus quadragintus) is the first Australian bird found to deliberately encourage trees to release manna, a sugary crystallised sap. In doing so it not only provides food for its young but might also engineer the environment in a way that benefits other Tasmanian animals.
Samuel Case and of the Australian National University in Canberra spent the second half of 2014 monitoring the birds, whose population has plummeted by 60 per cent in the last 18 years. 鈥淲e were ecstatic and surprised to discover a novel foraging behaviour,鈥� says Case.
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The birds deliberately clip the leaf stalks of the manna-gum tree, a species of eucalyptus, with their bills. In many cases the tree responds to the wounds by exuding sticky and nutritious manna gum over the next few days, which the birds harvest. Biologists call this foraging behaviour 鈥渕ining鈥� or 鈥渇arming鈥�.
鈥淢ining for tree exudates is an unusual foraging behaviour among birds,鈥� says Case. 鈥淭his is the first record of an Australian bird that mines trees.鈥�
鈥淭he behaviour of the forty-spotted pardalotes is strikingly similar to North American sapsuckers,鈥� says at Valparaiso University in Indiana, who studies similar behaviour in North American birds. 鈥淓specially interesting is the way the pardalotes returned to the same holes and widened them over time.鈥� This is something that sapsuckers do too.
Remarkable adaptation
The pardalote feeds its offspring almost exclusively on manna. Case and Edworthy found that it makes up about 85 per cent of a nestling鈥檚 diet 鈥� even though manna accounts for only about 2 per cent of the food available to the birds, as insects and other invertebrates are far more abundant.
The birds may prefer manna because it is rich in carbohydrates and easily metabolised nitrogen, says Case. 鈥淭hese birds are able to stimulate production of their most valued food resource during the nestling period, a remarkable adaptation.鈥�
Farming is seen in species right across the animal kingdom, including in some insects. 鈥淏ut it does appear to be rare overall,鈥� says Eberhardt. It鈥檚 not clear why that is the case: it isn鈥檛 necessarily more cognitively demanding to gather food this way, she says.
Other species of bird, including , eat manna, and so do mammals including the . But these animals don鈥檛 farm manna, so they almost certainly take advantage of the fact that the pardalote does.
鈥淸Pardalotes] may serve as eco-system engineers by stimulating food production for other manna-feeding species,鈥� says Case. That makes it all the more important to protect the species from extinction, he adds.
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