Forty-Spotted Pardalotes – Modern Day ‘Canaries in a Manna Mine’

Pardalotus quadragintus, more commonly known as the Forty-spotted Pardalote, is one of Australia’s endangered songbirds found mainly in the forests of Tasmania, notably on both Maria and Bruny Islands. These cute little birds measuring 9-10cm with olive green, grey and yellow variegated plumage, identifiable by some 40 plus tiny white dots on their wings, forage predominantly in the foliage of White Manna Gums (Eucalyptus viminalis). Recently however, researchers Samuel B Case & Amanda B Edworthy from the Research School of Biology, Australian National University, Canberra have recently discovered that these little birds have a specialised foraging skill.

This rare and fascinating skill could also be a clue as to why these birds are becoming endangered, which is linked to environmental change affecting the trees they feed on. To understand the importance of this link, is to first understand the trees themselves.

Certain Eucalytpus species such as the Manna Gum produce a crystallized exudate, which is a kind of sap that secretes from damaged surfaces of leaves and twigs[1]. As Manna is composed primarily of 60% sugars[2] as well as Nitrogen in the form of amino acids,[3] these building blocks of proteins become an important part of the diet of nestlings (and possibly) adult Pardalotes. In fact, Manna comprised around 75% of the food items provisioned to nestlings in one study at Bruny Island alone[4].

What researchers discovered during extensive observations of the adult birds while foraging and provisioning nestlings, was that while Manna secretion was often created by accidental damage to foliage, these birds were actively creating incisions on stem surfaces to generate production of the crystallized exudate. More interestingly, larger wounds were found to be maintained and widened over time, providing evidence of a ‘mining’ skill, which is a rare foraging behaviour. Unfortunately, it is also rare for songbirds to be solely reliant on one plant species.

Trunk of Eucalyptus viminalis

So, what is happening to the trees? Unfortunately, habitats of Tasmanian E. viminalis is becoming fragmented by land clearing and has undergone die-back, atrophy and poor sapling recruitment during a decade of drought due to climate change[5]. Manna also detaches easily from foliage in wind, rain and heat. While older trees provide larger canopies and more abundant supply, restoration of E. viminalis habitat is crucial to the future survival of these birds.

On a positive note, observations of their mining skills have taught researchers how they too can produce Manna flow for captive breeding programs should populations sadly decline to dangerous levels.

Let’s hope it doesn’t come to that.

 

 

 

 

 

 

 

References:

[1] Basden 1966, Steinbauer 1996

[2] Basden 1966

[3] Bosque & Pacheco 2000

[4] Woinarski & Bulman,1985

[5] Bryant 2010

Image Credits:

*Link to Article as Published on Gecko Hills to Headlands.

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