Posted on 19/12/2019 by Phillip Island Nature Parks
Better news for Shearwaters
Phillip Island Nature Parks researchers are pleased to report that, after a rocky start, things are looking up for Phillip Island’s Short-tailed shearwaters. Good numbers of birds have returned and there are eggs in burrows signalling a late, but positive start to the breeding season.
The 2019 Short-tailed shearwater breeding season has been extremely unusual. It started with the birds arriving from their 15,000 kilometre migration from waters around Alaska 10 -14 days later than normal. This is a significant delay for a migratory bird that has a very tight schedule to keep.
“The shearwater arrival at the end of September is usually very predictable,” says Nature Parks Deputy Research Director, Dr Duncan Sutherland.
“Initial numbers of birds arriving in the Phillip Island colony in October were very low, less than 10% seen in normal years.”
“Interestingly, the birds that did return were in good condition.”
“We didn’t know what had happened to the rest of the birds and whether they would actually return to breed this year.”
A collaborative research project between Phillip Island Nature Parks and the Victorian Ornithological Research Group includes regular visits to 180 burrows in the 1.4 million-bird colony and has slowly built a more positive picture.
“Although less than half the usual number were thought to have returned by November, numbers in the colony were increasing at each research visit.”
In November, the shearwaters undertake a two week ‘honeymoon’ in which they fly down to feed in Antarctic waters before returning to lay a single, large egg in their sand dune burrows.
Researchers visited the colony after this honeymoon trip and were very surprised and pleased to find that many more birds had returned to lay their egg and that the colony contained at least as many birds with eggs as in a normal year.
While this is great news, it still leaves many questions unanswered. Like - what’s really been going on with all those birds?
“We don’t know yet,” said Dr Sutherland.
“It could be poor food supplies in their feeding grounds in the Bering Sea near Alaska, or perhaps a lack of favourable winds may have delayed their migration. Another theory is that many of the birds may have initially bypassed their breeding colony on Phillip Island to forage in the Southern Ocean.”
The team is hoping to recover tracking devices that were deployed on birds over the last couple of years.
“Data from these devices should tell us when the birds actually undertook their migration this year and where they were spending their time once they reached the Southern Hemisphere.”
- Short-tailed shearwaters are a migratory seabird that flies over 15,000 kilometres from waters around Alaska to breed on Phillip Island each year.
- About 1.4 million shearwaters nest along Phillip Island’s coast – largely on land managed by the Nature Parks.
- In 2019, shearwaters started to return 10-14 days later than normal, a significant delay for this species whose return is normally very predictable.
- The number of birds in the breeding colony gradually grew leading up to mating and egg laying.
- The season is now looking very promising with better than average numbers of birds incubating an egg in their burrow.
- There are still many unanswered questions and researchers are hoping that trackers deployed over the past few years will reveal when the birds returned on their migration and where they’ve spent their time in the Southern Hemisphere.