SHORT-tailed Shearwaters are Phillip Island’s migratory marvels.
Not only do up to a million of them return to their island home each year, following a 16,000-kilometre flight, but they usually mate for life, sharing egg duties in the same burrow while their partner goes fishing, as far asway as the Antarctic.
This year, they were late arriving again from the Artic north and the Bering Sea between Russia and Alaska.
Known for their endurance and punctuality, they usually arrive like clockwork, within 48 hours of September 24, but not this year.
Numbers locally had been low until last weekend.
“The birds arrived over the weekend, later than expected, but they’re here in good numbers. Last year they were delayed as well,” said Deputy Director of Research at Phillip Island Nature Parks, Dr Duncan Sutherland.
“They could have been delayed for a lot of reasons. They could have been blown off track, which we don’t think has occurred, or there wasn’t enough wind.”
Dr Sutherland said Arctic sea ice extent was at its second lowest this year in the 42-year satellite record, only behind September 2012 with the result that the birds may have had to go further to feed.
“We’ll hear more of that later.
“But they got here a little late last year too and still had a successful breeding season and good numbers of young birds got away again towards the end of April.
“Of course, the adult birds were long gone by then,” said Dr Sutherland of the mass adult migration, initially to the Antarctic late March/early April before the long flight back to the north pole.
PINP’s research team will be monitoring the study sites over the next few weeks as this amazing cycle continues, admittedly a little late again this year.
Artic ice near record lows
Arctic sea ice extent average for September 2020 was 3.92 million square kilometers (1.51 million square miles), the second lowest in the 42-year satellite record. In July 2020, it was sitting at a record low.
Following the minimum seasonal extent, which occurred on September 15, ice growth quickly began along in the northern Beaufort, Chukchi, and East Siberian Seas. Expansion of the ice edge was also notable within the East Greenland Sea and within Canadian Arctic Archipelago.
By contrast, the ice edge in the Kara and Barents Seas remained relatively stable until the end of the month when it started to expand, and within the Laptev Sea the ice edge retreated slightly.
The Northern Sea Route remained open at the end of September whereas the Northwest Passage southerly route (Amundsen’s route) was blocked by ice. Ten days after the minimum extent was reached, the total extent climbed above 4 million square kilometers (1.54 million square miles) and by the end of the month the ice extent was tracking at 4.25 million square kilometers (1.64 million square miles), still second lowest in terms of daily extent.
Arctic air temperatures at the 925 hPa level (about 2,500 feet above the surface) remained overall above the 1981 to 2010 average during September. This warmth was primarily observed on the Eurasian side of the Arctic, where air temperatures along the coastal regions of the Laptev Sea reached up to 8 degrees Celsius (14 degrees Fahrenheit) above average.
Where the Short-tailed Shearwaters have been able to rely on the prevailing winds at the same time in September for 1000s of years, to assist them on their long journey south, something has seriously changed in the past few years to alter their previously metronomic departure.
It’s also impacting their fishing and is expected to ultimately affect their breeding.
Port Fairy colony fears
Down Port Fairy way, bird experts are concerned after the migratory shorebird colony failed to arrive on time for start of the breeding season again this year.
Last year only half of the 40,000-strong colony at Port Fairy’s Griffiths Island eventually turned up.
Prior to last weekend, the island’s bird count remains at zero more than a week after they were expected to arrive.
Birdlife Warrnambool president Peter Barrand raised the alarm 12 months ago when Griffiths Island’s normally punctual population arrived weeks late.
Those that did turn up were emaciated and exhausted.
“It was a disaster last year, and this year again they’ve failed to turn up on time,” Mr Barrand said.
Between 15,000 and 20,000 birds eventually arrived in Port Fairy last year, but the breeding rate among those birds was worryingly low.
Similar numbers are believed to have arrived in the past few days, but as the arrival time gets pushed back further, there are fears it will conflict with the limited time for breeding and the birds’ strong instincts for departure.
About the Shearwater
The Short-tailed Shearwater are migratory ocean birds. They usually have a lifespan of 15–19 years, but can live up to 38 years. Each year they travel around 16,000 kilometres to the Arctic and then return to southern Australia during summer. Large colonies of these birds rest on the sea in the late afternoon, and this is referred to as ‘rafting’.
They feed on krill, small fish and other marine creatures. Food is usually caught on the surface of the water but Short-tailed Shearwaters sometimes dive down up to 12 metres to feed among the weed on the sea-bottom.
Breeding Short-tailed Shearwaters mate and lay their eggs in burrows which are usually around one metre long. When they return to their breeding grounds in late September they usually reunite with the same partner of previous years and occupy their previous burrow or one nearby.
The burrow is prepared during nightly visits and the couple is very noisy, possibly to announce that the burrow is occupied.
Short-tailed Shearwaters rarely breed until they are five years old and it may take them longer than this to find a mate. They lay one egg from late November each year.
All females in all the different colonies lay their eggs within the same 12-day period. The male and female take turns incubating the egg for around 53 days until it hatches. To feed their chicks they have been known to fly to Antarctica and back to collect good food. This means flying 1000km-a-day for four days at a time.
They truly are a remarkable creature and Phillip Island has a key role to play in their survival… so too, it seems, does the climate.