Linking the food chain

07 April, 2010

Platypus field site
The platypus field site, upper Shoalhaven River, New South Wales.
Image: Julian Finn
Source: Museum Victoria

MV’s Richard Marchant has teamed up with Australia’s foremost expert on platypus to learn more about the feeding habits of these elusive monotremes.

Tom Grant, of the University of New South Wales, has been studying platypus in a stretch of the upper Shoalhaven River for over thirty years. Despite this site being surrounded by farms  the upper Shoalhaven, on the south coast of NSW, is home to a stable and healthy population of platypus (Ornithorhynchus anatinus).

Since the 1970s, Tom has observed several hundred animals and he estimates between 10 and 20 live at this study site. He captures platypus at dusk as they emerge from their burrows to feed, measuring and tagging individuals before releasing them unharmed. In 2009 he caught a female that he tagged when she was only a few months old, 20 years prior, making it the longest-lived platypus on record.

In 2009, Richard Marchant joined Tom in the field to help identify what the platypus eat. An expert in aquatic insects, Richard sampled the insect life available to foraging platypus using scuba diving equipment and a kind of underwater vacuum cleaner called an air-lift sampler. He will spend the next few months identifying the creatures and also those taken from the cheek pouches of platypus.

Platypus feed on the bottom of the river, remaining submerged for 20-30 seconds. “They come to the surface to chew up their food in their cheek pouches before swallowing it,” explained Richard. “It’s quite rare to find whole specimens in the cheek pouch samples; these samples just look like mud. It’s a bit of a detective job – if you know the fauna, you can identify the bits and pieces under the microscope.”

It turns out that platypus are quite picky eaters. “Mostly they’re eating larvae of dragonflies, mayflies and caddis flies,” said Richard. “There are other animals that are abundant in the bottom sediments, such as fly larvae, but we don’t find them in the cheek pouches.” It seems that platypus use their very sensitive bills not just to find food but to discriminate between prey items.

Richard’s investigation builds upon decades of work by Tom, including dietary studies from the 1970s. “There’s a lot that’s known about the platypus itself, but there’s very little that connects the biology of the platypus with what else is going on in the river. It’s understandable because the people who have done the work tend to be mammal specialists, and insect or freshwater invertebrate specialists like me have generally never looked at the platypus. But in fact it’s a major part of the river ecosystem and now we’re linking up the various parts of the food chain.”

View this video with transcript

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