Department of Statistical Sciences
University of Cape Town
| Avian Demography Unit
Department of Statistical Sciences University of Cape Town |
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ADU travels, expeditions and eventsStory & Photographs by Marienne de Villiers and John Cooper A. Introduced Aliens B. Country Cleanups C. Disturbance of Seals and Seabirds On 25th March, John Cooper and I set sail on the SA Agulhas, fondly known as the Red Taxi, for sub-Antarctic Marion Island. As Conservation Officer and Assistant CO respectively, our duties had begun some time prior to sailing.
Although Marion is remote, 2300 kms southeast of Cape Town, the island has suffered from the thoughtless introduction of alien species in the past. Not little green people with large ears and tube-like appendages, but cats, domestic mice and various plant and invertebrate species. By 1991 the cats had been finally eradicated, after years of intensive work by Marthan Bester (University of Pretoria) and his dedicated teams of cat hunters. Other introduced species are still hanging in there, however, and are a threat to the natural fauna and flora of the island. Prevention of the introduction of further aliens to the island, and the control or eradication of current problem species, are thus some of the management aims for this Special Nature Reserve. Our pre-sailing tasks included inspections of the stores of the Department of Environmental Affairs and Tourism, the stores of the Department of Public Works, and the SA Agulhas itself. During inspections, we kept an eagle-eye open for signs of rats, mice, insects, spiders and propagules. On the fourth day of the voyage to Marion, a Boot-washing Ceremony was held on the aft deck and involved much socialising and jollity as all bags, footwear and outer gear destined for the island were checked over and potential unwelcome guests collected for later identification. The landing gear of the helicopters used to supply the island were cleaned prior to arrival and for the first few days after disembarking, the campaign against aliens continued in full force on the island. All food and drink containers were inspected and an infestation of cockroaches in two of the containers of drinks was dealt with mercilessly.
Over 300 helicopter flights were flown during the takeover period. Whenever possible, I observed the effects of these flights on birds and seals in the vicinity. Rockhopper Penguins and Wandering Albatrosses showed minor signs of distress during flights, but no moulting Rockhoppers were observed to head for the sea to escape the disturbance, and no incubating or breeding Wanderers deserted their nests. In fact, a pair of courting albatrosses continued their romance throughout the takeover period, right next to the helipad. Southern Giant Petrels, on the other hand, panicked and took to the air even when helicopters were passing over at a height of 1000 feet. Fur Seals were also noticeably affected by helicopter flights, tending to panic and flee long before helicopters passed over the general area. The number of seals using the beach closest to base decreased by 25% in the first four days of flying. Few species (apart from Wanderers) were breeding during the takeover period but later in the year, the consequences of helicopter disturbance on the breeding success of certain species could be severe.
In the course of the country cleanups, John and I noticed that there was a great amount of variation in the way that Wandering Albatrosses reacted to being approached by humans on foot. For instance, a 35 year old French lady (born on Possession Island in the Crozets) would allow one to sit next to her and stroke her wing, while a 27 year old Marion-born male would utter loud and repeated threats while we were more than 100m away from his nest. John and I decided to attempt to address the question, "What variables predict the severity of reaction of a Wandering Albatross to a human approaching on foot?" We approached over 350 incubating or brooding adults and 73 solitary chicks, noting key reactions and the distance at which these took place. Analysis of the data is still in progress, but initial indications are that stage of breeding, previous breeding success and history of disturbance are more important factors in determining intensity of reaction than the age and sex of birds.
The process of alien eradication, and the prevention of the introduction of further aliens to Marion Island, is an ongoing one. The island clean-ups are by no means complete, and there is huge scope for further investigation into the effects of human disturbance on sub-Antarctic birds and seals. Watch this space for further developments… Thanks to DEA & T for permission to work on Marion Island, and Leonie Joubert, Greg Hofmeyr and Dumile Tshingana and the PWD boys for their help with the country cleanups. Thanks also to Peter Ryan and Rob Crawford for access to the Wandering Albatross database, and to Marine and Coastal Management for the loan of a digital camera for Wanderer ID photographs.
 
Office Avian Demography Unit Enquiries/More Information:adu-info@uct.ac.za Document posted 10 June 2003 |
