|
|
Falklands Conservation |
Introduction
On Saturday 24th May I was taken by Ali and Kevin Marsh, and accompanied by Ron and Fiona Rozee, to survey the islands of Double, Outer and Harpoon.
The weather was dry and sunny, with very little wind, and was therefore ideal for conducting such a survey. We were put ashore on each of the islands in turn, spending around an hour on each of Double and Harpoon, and about two hours on Outer, which is the largest of the three.
Clearly a more thorough survey performed during the breeding season would be required to fully assess the nature and abundance of species present on the islands, but the current survey provided sufficient information to determine the overall value of the islands in terms of ecological importance.
Results
It immediately became apparent that all of the islands have rats. Proof of their presence was observed in the form of droppings and burrows, and also the complete absence of Tussac-birds and wrens. In most cases the presence of rats would be sufficient grounds to discount islands as being of real interest for purchasing for conservation, but in view of the extreme richness of these islands in other ways, I think it sensible to consider further the implications of rats.
The presence of rats effectively denotes the absence of many small birds, notably Tussac-birds, Cobb's Wrens and small burrowing petrels, but rats are not considered to have a serious impact on larger bird species. If islands were sufficiently rich in species not affected by rats, then they may be worth considering on that basis alone. In addition, if such islands were sufficiently valuable as tussac islands in their own right, there is the option of purchasing with a view to using small islands such as these for a pilot study on rat eradication, at some point in the future.
All three islands were almost entirely covered in Tussac Grass but this factor aside each of the islands was unique in nature, and I will therefore consider each of them individually.
Outer Island
Total area: 48.2 acres (43.2 acres Tussac)
The most striking feature about Outer island is the Tussac Grass, which is denser and taller than that found even on Kidney Island. On Kidney Island it is quite possible to walk through the Tussac (albeit with some difficulty), because the pedestals are sufficiently spaced to allow channels between them: this was not the case on Outer Island. The majority of Outer Island has Tussac Grass which is completely impenetrable, and therefore the only means of crossing such areas is to climb to the top of the pedestals, and jump from pedestal to pedestal. The height of the Tussac is approaching 3m in these areas. It has almost certainly never been stocked, and can therefore be considered pristine in terms of tussac. Blue Grass was common on the island.
The only areas where the Tussac Grass has been eroded are on the south-east corner of the island, where large numbers of Sea Lion have worn highways into the tussac from the shore. The value of the island in terms of its Sea Lion population is confirmed by the Falklands Conservation Sea Lion Survey of 1995, which showed that the island held over 1% of the Falkland's breeding population of Sea Lion.
Other species breeding on the island are: Rock Shag (140 nests), Flightless Steamer Duck, Crested Duck, Night Herons, Blackish Oystercatchers, Pied Oystercatchers, Turkey Vultures and Ground Tyrants. Also present were about 300 King Shags, about 40 Snowy Sheathbills and around 30 Johnny Rooks. A few of the Johnny Rooks were adults, and there is a possibility that one or two pairs may breed on the island.
In view of the extremely high quality of the Tussac Grass on Outer Island, serious consideration should be given to a rat eradication programme. Were it not for the presence of rats, probably brought on by sealers during the last century, the island could have had an ecological value approaching that of Kidney Island. It is by no means certain to what degree a rat eradication programme would enhance the value of the island in terms of the smaller bird species, but it would be an ideal site at which to evaluate the benefits of rat eradication programmes in general. Such a programme should be relatively easy to conduct on an island of this size, and Outer Island provides an ideal opportunity to evaluate the benefits of rat eradication on an island with outstanding tussac.
Double Island
Total area: 22.2 acres (9.3 acres Tussac ,/ 3.] acres Dune)
Double Island consists of two small Tussac covered islands, joined in the centre by a neck of sand dune and sand beach. The Tussac Grass is fairly dense, but does not exceed 2m in height. This probably reflects the thinner soils of the island, and it is likely that the island has never been stocked. There is abundant Blue Grass on the island and an area of dune.
The island is home to a breeding population of Sooty Shearwaters, confirmed by the discovery of their burrows amongst the tussac, and the remains of a carcass in one of the burrows. There are only ten confirmed breeding sites for this species in the Falklands, and therefore its presence on Double Island is an important factor in considering the island's purchase. Other species breeding on the island are: Flightless Steamer Duck, Crested Duck, Blackish Oystercatcher, Pied Oystercatcher and Ground Tyrants. Also present were Sea Lion, Turkey Vultures, Upland Geese and about 10 Johnny Rooks.
In summary, the island is probably pristine in terms of tussac, with rats having been introduced by sealers during the last century. The island is mostly covered by Tussac Grass, but this does not attain the height found on some islands, probably as a result of the thinner soils found here. The Sooty Shearwaters are a significant find and give the island an important conservation status. This island would be an ideal candidate for carrying out rat eradication, since small burrowing petrels may well begin breeding here alongside the Sooty Shearwaters in the absence of rats.
Harpoon Island
Total area: 9.2 acres (7.4 acres Tussac)
Harpoon Island was apparently named so after the discovery of a harpoon on the island, which is now held in the museum. There are still remains of a large whale skeleton on the south of the island, with a rusty harpoon head amongst the bones. It seems reasonable to suppose that the rats were brought onto the island by whalers and sealers during the last century.
The island is entirely covered by fairly dense Tussac Grass, but this is less than 2m in height, probably as a result of the thin soils. Old farm records show that 43 sheep were grazed on the island between 1939 and 1940, so the island could not be described as pristine. Nevertheless, disturbance from stocking has been minimal.
The island is surrounded by an extensive rocky shore, which more than doubles the size of the island at low tide. This makes the island a haven for shore feeding birds. Species breeding on the island are: Blackish Oystercatchers, Pied Oystercatchers, Steamer Ducks and Crested Ducks. Also present were large numbers of Snowy Sheathbills, King Shags, Kelp Gulls, Dolphin Gulls and Johnny Rooks. Some of the 40 or so Johnny Rooks around the island were adults, but the island does not seem to offer suitable nesting sites, so these adults are probably transitory. Over 100 Sea Lions were on the island amongst the tussac, but it is uncertain whether any breed here.
Harpoon does not have any individual features which make it outstanding but it does hold large numbers of shorebirds, Sea Lions and Johnny Rooks which make it an appealing island in its entirety.
Summary
On first appearance the presence of rats is very detrimental to the appeal of the islands for conservation purposes. However in other ways the islands hold a wealth of wildlife. The pristine nature of the Tussac Grass, and the breeding population of Sea Lions make Outer Island a very worthy acquisition, even with the rats. Similarly the breeding population of Sooty Shearwaters make Double island a valuable acquisition. I believe that both of these islands should be seriously considered for purchase on this basis alone.
Islands of this size should be quite feasible for rat eradication on the basis of information so far obtained by Falklands Conservation and one could argue that if rat eradication is considered too daunting for islands of this size we could not seriously look towards much larger islands such as North-East Island. Both Outer and Double Island could be extremely valuable islands in the long term, following rat eradication. I feel that they would both be worthy acquisitions.
Harpoon Island is a slightly different situation: it is the smallest and therefore cheapest of the three islands, but still has a wealth of commoner species. It lacks any real rarities in terms of species or habitat, buts holds large numbers of Sea Lions and Johnny Rooks, as well as various shorebirds. It is not such a priority as Outer and Double.
As a final point it is worth consider the statement made in the Falkland island Foundation "Tussac Grass in the Falklands" Report, which states that:
Outer, Double and Harpoon Islands all appear to be examples of untouched tussac islands in an area where there are few examples remaining. It is recommended that they be considered for reserve status."
|
Patron: HRH The Duke of York CVO ADC Member of the International Union for Conservation of Nature | BirdLife International Representative |