Native and introduced mice are quietly pollinating Australian plants, study shows

Sometimes plants need a helping hand to reproduce. But what about a beak? Or a snout?

Most pollination is by animals, and perhaps the best-known pollinators are the birds and bees. Many plants rely on these flying animals to transfer pollen between flowers for sexual reproduction.

Now Australian scientists are discovering more grounded creatures — native and invasive rodents — play larger roles as pollinators than we realised.

And for some plants, such as certain banksia species, native rodents may be their primary pollinators.

The story has its roots in the 1970s, when researchers started to take notice of Australian mammals as pollinators.

Mammals that feed on nectar and pollen, such as honey possums and squirrel gliders, can get their head and body covered in pollen while feasting.

The marsupials can transport pollen to other flowers as they move on to the next meal.

But it wasn’t until recently the significance of ground-dwelling rodents as pollinators for Australian flora has emerged.

A 2023 study published in Australian Mammalogy, found high concentrations of pollen from heath-leaved banksia (Banksia ericifolia) on the snout of the grassland melomys (Melomys burtoni).

Southern Cross University wildlife ecologist and study co-author Ross Goldingay said rodents, such as melomys, invasive house mice and swamp rats, were the only mammals visiting heath-leaved banksia at the site in the north-east NSW heathlands.

“Mammals were doing as much pollination of Banksia ericifolia as birds and bees,” Professor Goldingay said.

“I think my studies were the first to provide compelling evidence for rodent pollination in Australia.”

A flower evolved for mice?

Many banksias appear to have evolved to target birds as pollinators.

A lot of their flowers are large, scentless and come in vibrant colours such as red which attract honey eater species.

But in the global biodiversity hotspot of WA’s South West region, there are some smelly and strange-looking banksia blooms you have to get on your belly to see.

“The flowers are hidden,” La Trobe University botanist Stanislaw Wawrzyczek said.

“The idea [from scientists] was that they are probably pollinated primarily by mammals and that they evolved specifically to attract mammals.”

Mr Warzyczek recently studied several of these bizarre species in the Kwongan heathlands north of Perth, including the awled honeypot (Banksia subulata), for work published in the Botanical Journal of the Linnean Society.

Using a combination of camera- and live traps, he and his co-authors found the native noodji (ash-grey mouse or Pseudomys albocinereus) and invasive house mouse were primary pollinators of the rare banksia, which is only found in a small region centred around WA’s Alexander Morrison National Park.

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“This one has more mice coming to the flowers than birds,” Mr Wawrzyczek said.

“Flowers are 2–3 centimetres from the ground so mice go a little on their hind legs … [and] lap nectar from the flower without climbing into the branches.

“Preventing mammals from visiting flowers significantly reduced [the transition from flower to fruit] in Banksia subulata.”

House mice and noodji look incredibly similar so it was too difficult to tell them apart from the camera-trap footage.

Mr Wawrzyczek said this meant he could not say what proportion of each visited the flowers.

But he thinks this research is the first to show a flower species that is primarily pollinated by rodents in Australia.

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University of Western Australia ecophysiologist Don Bradshaw, who was not involved in the research, said the study showed there was still a lot more to learn about native pollination and pollinators.

He was not surprised the noodji was a flower pollinator, given past observations of its diet.

“When studying this [species] some years ago with another of my students, Keith Morris, we found to our surprise that this ‘granivore’ also feeds on insects,” Professor Bradshaw said.

“This rodent is obviously a very [general] eater and the paper shows the value of field-based studies, which often challenge the conventional wisdom.”

What’s smell got to do with it?

Mr Wawrzyczek is still working on why mice are attracted to the awled honeypot.

One possibility is smell; the flower has a slight musky pungent scent.

Floral scents have been shown to attract rodents to South African flowers and Mr Wawrzyczek says he has pending research on the musk of Australian flora.

But the idea that smell is the primary attractant for mammals to flowers was also turned on its head by Mr Wawrzyczek’s recent study in the Kwongan heathland of WA.

Two scentless types of banksia — parrot bush (Banksia sessilis) and shaggy dryandra (Banksia splendida) — have colourful flowers that appear suited to birds.

Yet Mr Wawrzyczek found teeny honey possums could be the main contributors to fruit production in both species.

He also found a multitude of animal species were likely involved in pollination for some WA flowers.

For instance, dunnarts, birds, honey possums, mice and introduced bees all appeared to contribute to the pollination of bearded dryandra (Banksia shuttleworthiana).

A pollination spectrum

The bearded dryandra and its poly-pollinated ilk of the South West come as no surprise to University of Western Australia ecologist Mark Brundrett.

He said the region was one of the most complex locations in the world for flower pollination — if not the most complex.

It’s home to a broad diversity of plants, possibly due to poor soil quality and historical climate instability.

And with so many plants, there is strict competition for pollinators.

In a study published earlier this year in the Australian Journal of Botany, Dr Brundrett and his colleagues identified pollination strategies for almost 9,000 flora species.

More than 6,000 of them used insect pollination, and half of those involved flowers which sought individual species instead of many.

“Some species were associated with a particular bee,” Dr Brundrett said.

“There’s also buzz pollination, where a flower doesn’t open unless a bee buzzes at the right frequency.

“We also found more-than-expected plants with wind pollination in arid or sand environments … lands that grow after fire tend to be more wind pollinated.”

Mammals were likely under-represented in the dataset, as they were associated with pollinating only 36 species.

But Dr Brundrett said trying to track pollination in WA gets a lot more convoluted with some flowers switching between pollination strategies.

“Some Darwinias and Eremophilas have forms that are more bird-pollinated or insect-pollinated,” he said.

“It’s very complicated but we need to understand this if we’re looking after a lot of rare species in Australia.”