Biology / Environment

Is this tiny Australian bird an ecosystem engineer?

(Forty-spotted Pardalote photo by Francesco Veronesi via Flickr)

The Forty-spotted Pardalote is tiny – the endangered songbird measures just a palm’s width from head to tail. Yet its daily activities could be having a big impact in the Manna gum canopies where they forage, a recent study suggests.

Manna gums (Eucalyptus viminalis), along with a limited number of other species, secrete sap that crystallises into a fluffy white substance called manna. The sugary floss is a staple for canopy-dwellers – from birds like the Pardalote, to sugar gliders, possums and ants.

Now, research by Samuel Case and Amanda Edworthy at the Australian National University, suggests that the Pardalotes might not be simply collecting the manna they find, but actively ‘mining’ it from the trees. Previously, manna production was thought to be due to damage inflicted by insects.

Perched high in the manna gum canopy, Case and Edworthy got a first-hand glimpse of the mining behaviour. The Pardalotes were making tiny incisions on the stems of the Eucalypt trees. Evidence of their handiwork was also visible as cuts and larger gashes that appeared to be re-visited and widened over time.

To confirm whether the birds could indeed deliberately harvest manna, the researchers mimicked the damage caused by the notched bills of the bird – a feature not share by other Pardalotes.

Using the bill of a freeze-dried Forty-spotted Pardalote – and then a blade, so as not to wear out the precious specimen – they artificially damaged leaf stalks, bagged them and waited for the manna to flow. Of four Eucalypt species tested, only the Manna gum produced manna in the days following the experimental damage.

Only a handful of other birds are known to actively mine tree saps, and this is the first report of mining behaviour in an Australian bird.

The team saw the birds fiercely defending their manna crop from other birds. This is perhaps unsurprising, given that video footage of nests revealed that manna comprised over 80% of the diet for Pardalote nestlings.

There is, unfortunately, a downside. The Forty spotted Pardalote’s reliance on the manna from Manna gums makes it extremely finicky about where it calls home. Its habitat is currently restricted to less that 4500 ha of dry woodland, mostly on three islands off the coast of Tasmania in the far southeast of Australia.

Should the Forty-spotted Pardalote decline to the point of requiring captive breeding, the newfound method for artificially stimulating manna production could be invaluable.

The extent to which other species take advantage of the manna mining is unclear. However, the authors note that the Forty-spotted Pardalotes could serve as ecosystem engineers, bumping up manna production to sustain a range of species that rely on the valuable food resource.

Reference:

Case SB, Edworthy AB. 2016. First report of ‘mining’ as a feeding behaviour among Australian manna-feeding birds. Ibis, Published online March 10, 2016, doi:10.1111/ibi.12350

 

 

 

 

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