This week at Macquarie Island: 17 February 2017
Northern giant petrel chicks are counted; tradies go on an island tour and an update from our weed hunters.
Northern giant petrel chick census
Listed under the Agreement on the Conservation of Albatrosses and Petrels (ACAP), an international agreement coordinating efforts to mitigate known threats to albatross and petrel populations, the Macquarie Island NGP population is monitored annually as part of the albatross and petrel program.
In September each year a census of eggs laid is carried out on the featherbed. In January, this is followed up with a census of chicks to determine the breeding success for that year. Since MIPEP the NGPs appear to be steadily increasing in number with the highest number of breeding attempts recorded last September.
Recent weeks have seen a combined effort from the albatross team of Kim and Penny, wildlife ranger Marcus and numerous enthusiastic volunteers (thanks Esther, Marty, Murray, Greg, Gorge, Ali, Kane, Mizza, Dan, Alex and Laura!) to complete the January chick census.
Working out of station at the field hut at Bauer Bay, teams of two visited each nest in the study area to record chick presences. Volunteers coming in were a great help when trying to relocate nests recorded in September amongst the rapidly growing tussock. Chicks were fitted with an individual ID band, enabling them to be identified when they return to the island to breed in around eight years.
With the chick’s habit of regurgitating oily stomach contents onto the person banding them (their defence mechanism against predators), banding can be a messy job. Everyone on station was also treated to the occasional whiff of fish coming off returning banding teams. That stuff doesn’t seem to wash off!
Tradies on tour
A few weeks ago, myself and Mizza took a break from building the new boat shed and headed down island to help Wiggs service some hut equipment. Over four days we walked down to Hurd Point at the southern end of the station, visiting all of the five recreational huts. We were lucky enough to experience two perfect days of sunshine and no wind with spectacular views over the southern end of the island, including the rarely seen Major Lake.
The highlight of the trip was climbing in and out of Hurd Point, which involves sliding/climbing over 200 metres down a steep slope covered in tussock grass to reach Hurd Point Hut. This hut has the best view on the island, looking out over the Southern Ocean and a royal penguin colony.
On the way home we had more typical windy Macca weather, which was broken up by a quick stop in at Green Gorge where Marty greeted us with hot scones and joined us for the walk home. At 'four ways' (where the tracks meet) the party split, with the two more adventurous of us deciding to complete the circuit to cover all the huts by detouring past Bauer Bay – making our total trip 93 kilometres long!
Macquarie Island weed hunters
Rats, rabbits, mice, cats and weka come to mind when thinking of invasive species on Macquarie Island, but invasive plants would rarely rate a thought for most people. With the invasive mammals and birds eradicated, the most obvious ‘pests’ that remain on the island are three widespread weed species – wintergrass (Poa annua) and two species of chickweed (Cerastium fontanum and Stellaria media). All three species are common garden weeds in southern Australia and have been present on Macquarie since they (most probably) arrived in bedding and feed with sealing gangs. Two other weedy grass species have appeared recently and were quickly removed and several other weeds have been removed in past decades.
The impact of invasive animals in the sub–Antarctic is clear – slopes denuded by rabbit grazing and rodents predating on sea birds, but the impact of invasive plants can be less immediately obvious. The impacts of invasive plants can however be dramatic, for example Creeping Bentgrass (Agrostis stolonifera) has drastically altered stream vegetation on Marion Island, a similarly isolated island in the Southern Indian Ocean. On Macquarie we are seeing rapid changes in the vegetation following the eradication of rabbits and the end of their boom–bust grazing regime and we are now unsure how the invasive plant species will respond. Will they increase because they are no longer being eaten or decline as the native vegetation recovers and out-competes them?
We are on Macquarie Island this season studying one of the chickweed species, Stellaria media. We’ve been combing coastlines, searching streams and scaling waterfalls in order to map the distribution of this weed across the island. We have also tagged plants to see how long they live and how big they grow and determine how much seed they produce. At a number of sites we have also installed physical control trials to determine whether these methods can be used to effectively control Stellaria on Macquarie. Taken together this information will help us conclude whether Stellaria needs to be controlled on Macquarie Island, and whether or not its ecology and current distribution make it a likely candidate for eradication.
Interestingly, Stellaria is good to eat (and even sold to restaurants in Tassie!). On sub–Antarctic Marion Island where they receive no fresh vegetables at resupply, Stellaria is only common at a fair distance from the station as all the plants around the station have been eaten by the local populace – perhaps the promotion of Stellaria as a salad green could be the best control method we have!
Laura Williams and Alex Fergus
Macquarie Island was discovered in 1810 by commercial fur sealers, and over the ensuing 80 years, six feral animal species established populations on the island as well.
Dogs and cats were reported as being feral in 1820, European rabbit and weka (a NZ flightless bird introduced by the sealers for food) in the 1870s, and ship rat and house mouse reported established in the 1890, although they were both likely to have been present from much earlier. Cats, rabbits, wekas and rodents severely affected the island’s native fauna and flora with estimates that a population of about 500 cats was killing around 60,000 seabirds per year, and predation on burrowing seabirds by wekas was also high.
Damage from overgrazing by rabbits was noted as severe in the 1950s and continued as rabbit populations fluctuated over subsequent decades. Rabbit control work began in the 1960s with poisoning trialled and the introduction of the European rabbit flea, and then in 1978, the rabbit myxoma virus was introduced.
Opportunistic cat control began in 1974 and was increased as the rabbit populations decreased. By 1983, cats and wekas were increasing their predation of burrow–nesting seabirds, and a strategy was developed to target both these species. The weka population was also subject to cat predation and the eradication strategy took advantage of this. The last weka was shot in 1988, but cats remained common.
The cat eradication strategy grew from a single winter ranger in 1985 to a team of six in 1998 and employed techniques including hunting and trapping. The last cat was shot on the island in June 2000, bringing the total of cats destroyed to 1689. In late 2000, two dogs trained in cat detection were deployed to the island for the verification phase. These dog teams combed the island to make sure that all signs of cats were gone. The eradication was a success: a clear example of this was the return of grey petrels, which had not been recorded breeding on the island for over 100 years.
So wekas and cats were gone, but rabbits and rodents still remained and were now the dominant pest species with the feral cats gone. They were thriving and causing devastating damage to the island’s vulnerable vegetation, wildlife and geology… stay tuned for more next week.
The following publications used as sources: “Eradication of Cats (Felis Catus) from subantarctic Macquarie Island” by Susan A. Robinson and Geoffrey R. Copson; “Macquarie Island: from rabbits and rodents to recovery & renewal” Australia Govt – Department of the Environment; “Macquarie Island Pest Eradication Project” Tasmanian Parks & Wildlife service