This week at Macquarie Island: 3 February 2017
This week we catch up on white-headed petrels, expeditioners and the Australia Day swim, our unexpected beach visitor and Stay Here off on tour.
White-headed petrel monitoring
White–headed petrels are a threatened seabird that breed in burrows on Macquarie Island. They are one of the larger burrowing species (between 580 – 810 grams) and the most abundant and widely distributed of the petrels breeding on Macca.
Their global population is in decline due to interactions with invasive species (such as cats and rabbits) and the population on Macquarie Island is listed as vulnerable under the Tasmanian Threatened Species Act 1995. For these reasons, white–headed petrels were selected as a key species to monitor pre–and post–MIPEP (Macquarie Island Pest Eradication Program).
Over the past two weeks, Field Biologist Kim and myself have searched two of the long–term white–headed petrel sites. Our aim was to identify the number of breeding attempts within the site and reproduce photos of vegetation, which can be used to relate changes in their population to habitat. We found many white–headed petrels breeding in both sites – some with small chicks! In a couple of months these sites will be checked again to see how many of the breeding attempts produce full–grown chicks (i.e. were successful breeders). We even found some other burrowing species co-habitating the site – sooty shearwaters!
It was great to see the white–headed petrels have survived the cats and rabbits that were present on Macquarie Island. Their breeding sites are looking in pretty good condition this year, so hopefully they will have a good breeding season. The data collected this season will be incorporated into the long–term database and analysed in the coming months to assess their population status and trends. Fingers crossed for some more good news about the wildlife living and breeding here on Macquarie Island.
Australia Day at Macquarie
Weather can make or break an event here on the island: on Australia Day we were lucky enough to get a sunshiny break just as it was time for the traditional two beaches swim.
Swimmers met in the middle of the isthmus for a photo opportunity and then followed the Australian flags from Buckles Bay on the east across to West Beach for a quick dip on both sides of the isthmus. As ever, wildlife spotters and a lifeguard were on hand. Atmospheric scientist Murray was able to launch one of his UAV's (unmanned aerial vehicles) and got some great aerial shots of the action.
Afterwards a hot spa was called for and was happily filled to capacity, followed by a big cooked brunch and a viewing of the Governor–General's speech. A lazy afternoon with some cricket and a spit BBQ followed, which finished another pleasant day off on the island.
Sperm whale washes ashore
This week we have had an unusual arrival to station: a large male sperm whale carcass. We have become used to seeing animal carcasses on Macquarie Island, with large male elephant seal fights ending the life of some individuals and giant petrels and skua predating on penguins and other seabirds. But this is the first whale we have seen!
These are majestic creatures that we rarely get to see and it is certainly sad to see one in this state. We have all been in awe of the animal’s sheer size: approximately 14.5 metres long according to photos taken with Murray’s drone and probably weighing around 40 tons.
It has also been fascinating to see the island’s resident scavengers make use of the novel food source. The whale skin appears to be quite tough, leaving the giant petrels, skua and kelp gulls to feed on the skin, fat and other tissues as they float ashore. And with the predators focused on this novel food source, the local prey (i.e. penguins and other seabirds) might get some reprieve! It should also get those predators well stocked with energy stores for their winter migrations.
Initially the whale carcass was in the surf zone, but in the last couple of days it was washed ashore and we have been able to collect some precious samples to help us understand more about these amazing animals. So far it has been possible to collect a skin biopsy, teeth, and a blubber sample. The skin and the teeth samples will be very useful for genetic analysis and ageing, respectively, and the blubber can be analysed for pollutants.
Unlike some of the other carcasses on the island, the whale carcass is probably going to be with us for a while. It is times like these we are grateful for the intense winds and cold temperatures so typical of Macquarie Island – without them the smell would certainly linger a lot more! That said, on days of low winds the smell has certainly penetrated station – guess that is life on a nature reserve for you!
Stay Here goes there
This weekend Macquarie Islanders are conducting the first (that we know of anyway) 24 hour island relay to 'walk' Stay Here to Hurd Point and back, a distance of approximately 75 kilometres.
As part of an inter–station ten kilometre challenge, we thought we'd up the ante for ourselves (as most of us are used to a long walk), and try and raise some money for Guide Dogs Tasmania at the same time.
‘Popping’ out of the ocean floor isn’t all that makes our island look like it does. Living in the southern ocean in the middle of the "furious fifties" means the elements have a constant effect on the shape of the landscape. Wave erosion impacts the land as soon as it rises above sea level, with the western side of the island being far more exposed than the east due to prevailing winds being from the north–west. This is evident in the scalloped shape of the coast which has been eroded by wave after pounding wave.
Extensive faulting, which controls earthquake activity, has been another major influence on the continued shaping of the island. There are many large and active faults which have created fault dammed lakes and been responsible for the location of major landforms. Earthquakes can also trigger major landslips, the scars of which cover many of the island’s slopes. It is estimated that an earthquake of magnitude 7.5 on the Richter scale shakes the island every decade. (Our strongest last year was 6.1 in September).
Glaciation was thought by geologists to be the dominant land-forming process up until the mid-1980s, however beach deposits discovered recently over a wide altitudinal range discount extensive glaciation.
Today, other active processes shaping the island are associated with water freezing and thawing: in particular frost heave, which is caused when water percolates into topsoil and expands as it freezes, loosening the soil surface and fine material which can then be removed by strong winds and surface water flow.
Freezing and thawing are also thought to be the major contributors to the terraces, or vegetation stripes which form on the island. On the terrace, the risers (sloping parts) are generally vegetated, while the treads (‘flat’ parts) are gravelled. This process is most active on the riser and the dislodged material falls into the tread. It moves slowly across the tread (which actually slope very slightly) and then down the adjacent riser. Vegetated risers probably indicate that the terraces are not currently active.
And then there is, almost always, the wind: it prunes the plants, removes finer material from bare areas and scours other areas with materials it blows about. Most expeditioners are familiar with the joy of a quick sand exfoliation facial while crossing the isthmus…
All the knowledgeable bits for this article are taken from the TasPWS booklet: ‘A new arrival: the geological development of a young island’ by Michael Pemberton, Garry Davidson and Jennifer Burton.