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201306Nov20:18

Wedge-​tailed eagle flew to Tas­ma­nia, sci­en­tists say

Infor­ma­tion
pub­lished 06 Novem­ber 2013 | mod­i­fied 03 Novem­ber 2014
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Researchers have found that the Tas­man­ian sub-​species of Australia’s largest bird of prey, the wedge-​tailed eagle, prob­a­bly flew to the island in the past 100-​plus years and did not develop sep­a­rately when Tas­ma­nia was cut off from the mainland.

Tasmanian wedge-tailed eagleDr Chris Bur­ridge from the Uni­ver­sity of Tas­ma­nia School of Zool­ogy said the researchers demon­strated that the endan­gered Tas­man­ian wedge-​tailed eagle (Aquila audax fleayi) was not ‘life-​boated’ on Tas­ma­nia by sea-​level rise, but instead was recently estab­lished by indi­vid­u­als that flew across Bass Strait. The find­ings of the study led by Bur­ridge were pub­lished on 30 Octo­ber in The Pro­ceed­ings of The Royal Soci­ety B.

“Pop­u­la­tions on con­ti­nen­tal islands such as Tas­ma­nia are often dis­tin­guish­able from main­land rel­a­tives in fea­tures such as body size, appear­ance or behav­iour,” Bur­ridge said. “In the case of the wedge-​tailed eagle, Tas­man­ian adults are darker in colour, with larger bod­ies and roost only in trees.”

It is com­monly assumed that such dif­fer­ences devel­oped dur­ing iso­la­tion caused by sea-​level rise after the Last Glacial Max­i­mum 18,000 years ago but we’ve found the cur­rent birds’ ances­tors colonised Tas­ma­nia by tra­vers­ing a marine barrier.
(Dr Chris Bur­ridge, Uni­ver­sity of Tas­ma­nia School of Zoology)

The sci­en­tists genet­i­cally tested 224 indi­vid­ual birds — 49 from the main­land and 175 from Tas­ma­nia. They included exist­ing museum spec­i­mens, cap­tive indi­vid­u­als, shed feath­ers and a Tas­man­ian Gov­ern­ment frozen col­lec­tion of deceased indi­vid­u­als col­lected between 1996 and 2012. The sci­en­tists mea­sured lev­els of genetic vari­a­tion between the Tas­man­ian and main­land birds with the expec­ta­tion that the Tas­man­ian pop­u­la­tion would exhibit lower variation.

Dr Bur­ridge said the sci­en­tists con­cluded that the Tas­man­ian pop­u­la­tion of wedge-​tailed eagle became iso­lated very recently from the main­land pop­u­la­tion, and cer­tainly not as long ago as the flood­ing of Bass Strait 13,000 years ago. “In addi­tion, a vagrant wedge-​tailed eagle has recorded on King Island in Reg Green’s book Birds of Tas­ma­nia,” he said. “If this is cor­rect it pro­vides evi­dence of marine dis­per­sal over short time scales. Indi­vid­u­als on Cur­tis and Rodondo Islands in Bass Strait are also likely examples.”

The fact that the Tas­man­ian Abo­rig­ines also had a name for the bird, Nairana, sug­gests that translo­ca­tion by Euro­peans is unlikely but there is some doubt as to whether this name was ascribed specif­i­cally to the wedge-​tailed eagle or to other rap­tors as well.

Unfor­tu­nately A. audax fleayi is a threat­ened sub-​species, and the sci­en­tists’ report empha­sised lower genetic vari­a­tion rel­a­tive to the main­land sub­species, A. audax audax, and the pos­si­bil­ity that it is suf­fer­ing from inbreed­ing depression.


(Source: Uni­ver­sity of Tas­ma­nia media release, 01.11.2013)


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