Europa Island Scientific Mission 7Th November 2008 – 6Th January 2009
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Europa Island Scientific Mission 7th November 2008 – 6th January 2009 James Russell and Lise Ruffino Université de la Réunion and Institut Méditerranéen d’Ecologie et de Paléoécologie Summary Two ecologists visited Europa Island for nine weeks, completing a six month study of the seabird community. Intensive studies were made of red-tailed tropicbird breeding success and loggers were attached to 25 breeding individuals. Ongoing work continued on white-tailed tropicbirds (breeding success, chick growth, diet), red-footed boobies (breeding success, chick growth, diet), fregatebirds (breeding success), caspian terns (distribution) and barn owls (distribution). 73 one hectare quadrats systematically located across the island were re-sampled for tropicbird nest density (both species). Problems were encountered with the military on the island. Introduction Europa (2223 ha; 22°21’S, 40°21’E) is a coralline atoll lying in the southern Mozambique Channel (Fig. 1). It is classified as a nature reserve in the Îles Éparses managed by the Terres Australes et Antarctiques Françaises (TAAF) as French overseas territories. The north-western area of the island about the airstrip is dominated by 5 m canopy dry indigenous forest composed of Euphorbia stenoclada and Ficus marmorata. At the northern point within this area approximately 45 ha is a historical sisal plantation (Agave sisalina and Furcraea foetida). The remainder of the island is 0.5 m height plains of herbaceous Sclerodactylon macrostachyum, which periodically floods following tropical cyclones. The large lagoon supports an additional 836 ha of mangrove (Rhizophora mucronata) and a 2.65 ha islet at the northern entrance. The only resident land birds are Europa white-eyes (Zosterops maderaspatana voeltzkowi), pied crows (Corvus albus) and barn owls (Tyto alba). The island is a regionally important breeding site for red and white tailed tropicbirds (Phaethon rubricauda and P. lepturus), greater and lesser frigatebirds (Fregata minor and F. ariel), red footed boobies (Sula sula), sooty terns (Sterna fuscata) and green turtles (Chelonia mydas). The island is part of a long-term research programme managed by the Marine Ecology laboratory (ECOMAR) at the Université de la Réunion. In 2008 a concerted effort was made to simultaneously study the entire seabird community from June to December (6 months). We describe here the observations and studies made during the last mission from November 2008 to January 2009. 1 Figure 1: Western Indian Ocean Islands with Europa inset. Buildings and airstrips are indicated. Red-Tailed Tropicbirds and Rats Red-tailed tropicbirds commence breeding in October with aerial displays, and laying occurs throughout November and December. We monitored a total of 140 nests (Table 1). Site Nests Notes champ de tir 40 rat control island 80 no control islet 20 rat eradication Table 1: Nest monitoring sites Nest density was highest in the ‘champ de tir’ (shooting range). Rats were locally eradicated in November in an approximately 2.65 ha area using 36 live-traps. A total of 36 ‘resident’ rats were removed. 22 traps were used for ongoing ‘maintenance’ of the rat-free area in December, and a further 10 ‘immigrant’ rats were removed. The rate of immigration was surprisingly low, especially given rats were already breeding (juveniles were captured). On the small 2.65 ha islet in the lagoon rats were eradicated in late November using 36 live-traps. Only 7 rats were caught, although this included juveniles. A further week of 2 trapping without success suggested all rats had been caught. Rats on the islet displayed a unique grey pelage on the belly previously unobserved on Europa. Following rat eradication on the islet, trapping was undertaken on the eastern and western coasts of the lagoon to obtain comparative genetic samples to determine the source of invasion of the islet. 25% of rats on the eastern coast had identical grey pelage. All other rats caught (75% on east and 100% on west) had the common brown- white pelage. Despite rat control and eradication predation of red-tailed tropicbird nests remained common. At the champ de tir most predation events could be attributed to crabs. On the islet most predation events could be attributed to crows (or possibly owls). Through the main island where no control was undertaken, predation was most commonly by rats, although crows and owls would also have contributed. This suggests that nest mortality is compensatory, i.e. the removal of one predator does not decrease predation as ultimately another predator will eventually predate the nest. This poses a complex conservation problem. Overall nest survival was low, and this is likely to be having a significant impact on red-tailed tropicbird recruitment and ultimately population size. Similar nest survival monitoring suggested nest mortality of the smaller white-tailed tropicbird was even higher, approaching 100%. 146 red-tailed tropicbirds were banded, with particular emphasis on banding both adults of breeding pairs around the champ de tir, and breeding pairs on the islet. 25 recaptures of previously banded birds were made, predominantly of recently banded birds around the champ de tir and météo station (2007-2008), and of historically banded birds around the lagoon and islet (1995-1998). Records are kept at the ECOMAR laboratory. Morphological measurements (weight, beak, tarsus and wing length) were collected for 166 birds. Habitat was recorded for each nest monitored (plant species, canopy height and vegetation density). The aim of this work was to provide a comparative study to the previous doctoral work by Matthieu Le Corre from 1995-1998. GLS Loggers were placed on 25 individuals to monitor at-sea foraging behaviour during the incubation and chick-rearing period. Loggers were placed predominantly on birds around the champ de tir rat control area. Despite rat control nest mortality remained high, and most nests where adults had been fitted with loggers had failed by the end of the mission. Loggers will be more difficult to recover as adults will need to be relocated. 3 Seabird Community Monitoring of reproductive success of greater and lesser fregatebirds and red-footed boobies continued. Growth rates of 28 red-footed booby chicks were also monitored. Growth rates of white-tailed tropicbird chicks were difficult to measure as chicks were often predated rapidly. Regurgitate was opportunistically collected from red-footed boobies, and red and white-tailed tropicbirds. Nine barn owl nests were checked for signs of breeding, but none was found. Barn owl nests were located in crevices and full of rat and occasionally tropicbird skeletons. Regurgitated pellets were collected. A dead white-tailed tropicbird was collected for the Natural History Museum of Reunion. Quadrats 73 one hectare quadrats systematically and randomly located across the island (Fig. 2) were thoroughly searched by two people (15 to 30 min) for the presence of nesting white and red tailed tropicbirds. Red-tailed tropicbirds were generally easy to locate, while white-tailed tropicbird nests were much more difficult to detect, and so it can not be assumed that all white-tailed tropicbird nests were located. Some quadrats were located in difficult vegetation (e.g. Pemphis or fallen Euphorbia) and this further complicated surveying. Red-tailed tropicbirds are semi-colonial and were commonly found nesting under Psiadia shrubs and especially around the edges of Pemphis vegetation. White-tailed tropicbirds are not colonial and were usually found under fallen Euphorbia trees or in coral crevices. Figure 2: Systematically randomly placed 1 ha quadrats (73) for monitoring tropicbird nest density. 4 Miscellaneous Sisal is spreading across the island, and some satellite populations were located (Table 2). Rubbish piles were also found well outside human habitation (Table 2). Invasive plants are likely to become an increasing problem on Europa as they spread across the island. Ongoing introductions are likely given the lack of any quarantine for cargo to the island. Item Latitude (S) Longitude (E) sisal 22.35282 40.34282 sisal 22.35996 40.36409 sisal 22.34255 40.34297 rubbish 22.34894 40.34208 rubbish 22.35294 40.35485 Table 2: GPS locations of satellite sisal and rubbish Military Ongoing problems were encountered interacting with the military and gendarme on the island. These problems are recurrent for all missions to the Îles Éparses, although can vary greatly depending on the respective personalities of the gendarme and military. Ultimately, they diminish greatly the value of these islands as Nature Reserves. Fishing (sharks and others fish) is a widespread and indeed even encouraged activity, by both the military and gendarme. Given that all fishing is banned within the Îles Éparses (see arrêté 18 Nov 1975 and 15 Feb 1994) this is completely inappropriate and unacceptable. Over 20 sharks were caught in 2 months on Europa. This is not sustainable and is likely to be impacting the local population. Poor management of buildings leads to freshwater availability which supplements the populations of crows and goats. This supports elevated populations of introduced species which go on to damage the ecosystem (e.g. crows predating tropicbird nests). This is unacceptable in a Nature Reserve (see arrêté 18 Nov 1975 and 6 Aug 1981). Protected wildlife was harassed (turtles disturbed in the lagoon, fregatebirds attacked nesting tropicbirds disturbed and baby turtles killed). This is unacceptable in a Nature Reserve (see Arréte 18 Nov 1975 and 6 Aug 1981). The gendarme and military do not understand nor appreciate the work of scientists, who in many cases are young students volunteering their time. Threats are made to remove scientific access to 'gendarmerie materials' such as the fridge and washing machine located in the météo station (‘gendarmerie’). It is abundantly clear that the military and gendarme would benefit greatly from a 30 minute presentation with questions and answers on the biological value of the Îles Éparses. Upon arrival the detachment had almost no understanding of the nature and importance of biodiversity and conservation on the island, yet when prompted, some were quite interested in learning more.