With heavy hearts Christine and I have now left Bird Island after a prolonged seabird-watching experience. It has been an exciting year on an extraordinary island. We arrived in June in time to observe the Sooty Terns’ arrival and egg laying, watched their feeding movements, and saw chicks hatch. After a break we returned in August to see the deployment of satellite tags under a project led by Rachel Bristol and funded by SeyCCAT (see blogs of 20 June, 5 July, 26 and 31 August 2019), on chicks on the point of their departure for the open ocean. We witnessed huge numbers of juveniles as they learned their basic flying skills and on our most recent visit in late September, we found that most adults and young have now left the island, signifying the closing stages of the 2019 breeding season.
Early descriptions of Bird Island, dating from the late 18th century, reported a treeless plain with “innumerable” seabirds. Most of these would have been Sooty Terns but descriptions also suggested that Brown Noddies, Masked and Brown Boobies nested there. In the late 19th and early 20th centuries human occupation began to inflict major changes. The island’s soils were stripped of centuries of accumulated seabird guano, for export as fertiliser, and the open plain was converted to coconut plantation, leading to the loss of most of the birds. The humans also had an appetite for birds and their eggs, putting more pressure on the declining populations and eventually leading to the loss of Masked and Brown Boobies as breeding species and the reduction of the Sooty Tern colony to a shadow of its former state.
After these potentially catastrophic environmental changes to create a productive working island, how did Bird retain its eponymous status as one of the tropical world’s seabird havens? It is matched in Seychelles and elsewhere only by islands managed specifically for conservation and restricted, tightly controlled, human access. On Bird, however, tourists can stay as guests of the birds and live among them – this allows tourists to “get up close” to the birds, and the more inquisitive birds to “get up close” to the human visitors!
When I first visited the island in 1972, Guy Savy who, with his uncle Robert Delorie, had bought Bird Island in 1967, was in the process of constructing Seychelles’ first ecotourism venture. This had led to another trauma for the island: Black Rats were introduced in a shipment of palm leaves for use as thatching for the rustic tourist accommodation. Rats thrived on the island until their eradication in 1996, along with the removal of rabbits that had also gained a foothold following the introduction of some as pets.
Guy and Robert recognised the potential value of birds to tourism, however, and began clearing coconut trees around the small remnant population of Sooty Terns that had survived on the north-west coast. Sooty Terns responded by occupying the cleared area and rapidly increased their numbers. Brown Noddies also survived, having adapted to nesting in trees, especially the crowns of the planted coconut trees. White-tailed Tropicbirds and White Terns found suitable nest sites in Casuarina trees that had originally been planted to provide windbreaks for the coconut trees. Sub-terranean nesting Wedge-tailed Shearwaters had also survived, despite their chicks figuring high on the list of birds valued as a food source. However, the construction of the airstrips (yes, two were built in the early 1970s although only one now remains in use today) led to the destruction of the underground burrow nest sites of many of them, along with Brown Noddy nest sites that had occupied the many coconut trees that were felled to facilitate the impending arrival of tourists.
For densely nesting Sooty Terns, the maintenance of open ground is essential. After the clearance of some of the coconut plantation this was achieved initially by the annual burning of grass in the colony area, but this was hit-and-miss and in some years April/May rains made burning impossible. Vegetation management was subsequently achieved by a tractor-driven gang mower, but this was subject to frequent breakdowns. In 2016 a purpose-built modern grass mower was bought for maintenance of the airstrip, lawns around the hotel, and the Sooty Tern colony. Following the new mower’s introduction, much of the grass in the Sooty Tern colony has been transformed to comprise largely of indigenous plants that are much more conducive to Sooty Tern nesting. This resulted in 2019 to some parts of the colony supporting more than seven nests/m2; we have never before recorded such a high nest density!
Lesser Noddies are obligate tree-nesters. In the 1970s, tens of thousands of them flew in each evening to roost overnight in treetops and in 1984 the first nests were recorded, despite the continuing presence of rats. The Lesser Noddies appear to have been responsible for some beneficial woodland management by importing seeds of the Mapou tree (more widely known as “Lettuce tree”, Pisonia grandis); its seeds stick to birds’ feathers, leading birds to be the plant’s main dispersal mechanism. This resulted in the establishment of this broadleaved tree among coconut trees remaining from the old plantation, producing a valuable and attractive mixed woodland. Mapou trees are favoured nesting sites for Lesser Noddies and their establishment, together with the landscape planting of other broadleaved trees around the hotel, has led the Lesser Noddy to become the dominant breeding seabird in this woodland habitat.
The rats’ removal in 1996 paved the way for Brown Noddies to resume nesting on the ground, which they have done mainly around the hotel, while elsewhere on the island they nest abundantly in coconut crowns, Casuarina trees and bushes. White Terns also benefitted from the absence of rats and began nesting on ledges in new buildings, including those of the hotel, on which they laid eggs.
The resulting huge numbers (almost certainly more than a million birds but numbers are difficult to estimate precisely) of nesting terns and noddies inadvertently provided a supply of easily accessible food to the giants among tropical seabirds – Greater and Lesser Frigatebirds. Some of these birds are present throughout the day during the Sooty Tern and Noddy breeding seasons, sleeping, preening and moulting in their roosts high in Casuarina trees. But numbers are greatly augmented in the evening and after dark by birds that have been feeding in the vicinity of the island by aerobatically chasing terns. This stimulates the terns to regurgitate the food they have procured during the day, following which the Frigatebirds catch the food items in the air or pick them up from the sea surface.
Off the east coast, Frigatebirds sometimes also chase Wedge-tailed Shearwaters, of which thousands can sometimes be seen outside the reef in the afternoons. Some shearwaters approach the island at dusk but the main arrival is after dark, when their eerie calls signify widespread burrow occupation among dense bush vegetation over a large area on both sides of the airstrip, around Hirondelle in the north-east and some around the south of the island – no census has been attempted but thousands of pairs appear to be involved.
For many years we have noticed that daytime groups of roosting Frigatebirds sometimes include immature Red-footed Boobies. This year we noticed far more boobies arriving at the island from the north-west each evening and a count on 31 August revealed a minimum of 510, but as darkness fell boobies were still arriving.
With a breeding seabird fauna involving many thousands of Sooty Terns, Brown and Lesser Noddies and Wedge-tailed Shearwaters, along with smaller numbers of White Terns and White-tailed Tropicbirds, and hundreds of roosting Greater and Lesser Frigatebirds, Red-footed Boobies and sometimes Bridled Terns, Bird Island clearly remains a magnet for tropical Indian Ocean seabirds. Tracking studies have shown that tiny Bird Island attracts Sooty Terns to breed after dispersing over most of the Indian Ocean north of about 24 degrees south, highlighting the island’s international importance.
The success of the island’s attraction to seabirds has presented some problems, however. In the early 2000s, Sooty Terns occupied all of the areas that had been cleared for them. Furthermore, they began to occupy other areas of open ground, including the staff village and hotel, and the airstrip! Their incursion into the staff village, where the extremely loud noise of Sooty Terns throughout the night was depriving people of sleep, was curtailed by reversing some of the habitat management previously undertaken: young coconut trees were planted to the north of the housing. This successfully deterred birds from nesting close to the residential area.
This approach could not be employed on the airstrip, where landing aircraft killed and injured birds and risked damage to propellers and engines. To help to alleviate this problem, birds nesting on the airstrip were dissuaded by removing their eggs and by lighting bonfires along the runway margins. This partial solution was subsequently accompanied by a decision, sanctioned by the Ministry of Environment, Energy and Climate Change, to harvest Sooty Tern eggs from part of the nesting area closest to the airstrip. The eggs are sold as a traditional delicacy on the main populated islands and some of the funds generated are used to support environmental management on the Bird Island to maintain and protect bird numbers and diversity.
Bird Island survives in its present state as a world-renowned seabird reserve through protection and balanced habitat management. It also supports diverse marine life, including large numbers of nesting turtles (the largest population of nesting Green Turtles in the main island group) and fishes (including several species of shark).
The island remains unique as a major seabird island where tourists can stay and experience the 24-hour/day activities of the birds, being lulled to sleep by continuous Noddy calls, having to deviate from straight-line walking to avoid treading on ground nesting Brown Noddies, and being able to take close-up photographs of the birds without having to resort to powerful telephoto lenses!