

vHive visited Bird Island in the Seychelles to assess bird health in the sooty tern breeding population (approximately 1 million) and other species (whilst also marvelling at the spectacular island). We were particularly mindful of the effects of the H5N1 avian influenza strain on sea bird colonies around the world. Our non-scientific survey (we would refer you to Chris Feare’s and Christine Larose’s work, with colleagues, including on Bird Island for hard science) revealed that whilst a few dead birds were seen (<5) these were likely resultant of frigatebird attack, fledglings who lost their parents, or other non-infectious disease. The sooty tern and noddy fledglings and chicks were in noisy good health, apparently. The island is rat-free, and the human population, even with tourists included, is tiny. Thus, the eco-friendly ethos of the island’s owners has seemingly created a success story that is a marvel for all bird enthusiasts.

Bird Island in the Seychelles is renowned for its populations of sooty terns (Onychoprion fuscatus) and other magnificent species including the white tern (Gygis alba), brown noddy (Anous stolidus), and lesser frigatebird (Fregata ariel). We deliberately chose to visit the island when the sooty tern chicks were of a reasonable age (a few weeks to several months) so to assess the newborn vigour, as well as the parents. We must stress, this was not a scientific expedition and therefore, we took no samples. We visually assessed the status of the bird populations, questioning health but also entranced by the majesty of the Bird Island avian experience. Chris Feare’s and Christine Larose’s article on Bird Island explores the science and ecology in more detail (Feare, 2019).
Bird Island is an isolated island of about 120 acres, 100km north of the main Seychellois island of Mahé, and home to almost a million sooty terns during the breeding season (April to October). It is also home to thousands of lesser noddies (Anous tenuirostris), brown noddies (Anous stolidus), and more recently, red footed boobies (Sula sula) (Feare, 2021).
A selection of Bird Species on Bird Island







The first thing that strikes you when stepping off the 9-seater aeroplane that delivers you to Bird Island, is the sheer number of birds in flight and the unique soundscape, relentlessly carrying on through the night (see video below). The audible and visual experience of Bird Island is remarkable, especially when coupled with pristine beaches and beautiful aquatic life seen with simple snorkelling gear. A highly pelagic species seen in abundance on the island is the lesser frigatebird (Fregata ariel). Their soaring ability is well documented, and the large flocks circling overhead is another amazing spectacle offered by the Island.
The ethos of Bird Island now surrounds conservation, with initiatives on the Sooty Tern, the White-tailed Tropicbird Rehabilitation, and the Seychelles Sunbird Translocation Projects. The Sooty tern species feed on squid and small fish by dipping into the surface of the sea as they do not swim. They regurgitate the food for the chicks, also supplying them with sea water. Juveniles leave the island at around 9-10 weeks old to travel across the Indian Ocean. Trackers have sited sooty terns in the Comoros region, around the East Ridge, Arabian Sea, the Mozambique Channel, and the Chagos Marine Protected Area; with one ringed 5-month-old, born on Bird Island, being tracked to Northern Australia. Adults return to the island to breed (younger birds spend 5 years away before so doing).

The white tern, which has both beauty and grace (coupled with precarious egg laying practices) has long been the subject of concern for conservationists in the Seychelles, but the population on Bird Island looked vigorous and well. There were many white tern chicks and fledglings on their branches near where they were hatched, swaying in the Trade Winds. The sooty tern chicks looked extremely robust as did the noddy populations.

Whilst the pelagic lifestyle of sooty terns may limit their contact with other avian species, sooty terns nest very close together (6-7 nests per square meter over a large area) (Trevail et al., 2023). This intimate mixing of birds on the Island could, in theory, spread a virus between parents and chicks very rapidly, potentially leading to starvation of chicks following parent infection and mortality.
Impact of HPAI H5N1
The current strain of Highly Pathogenic Avian Influenza (HPAI H5N1 or H5N1) has had a significant impact on seabird populations. For example, over 9,000 puffins were killed on the Farne Islands due to avian influenza. These islands are relatively small compared to Bird Island in terms of surface area (approximately one tenth and bird population about one eight). Other island populations have been found to contain HPAI H5N1. For example, the remote island of South Georgia, a haven for wildlife has HPAI positive populations of brown skuas (Stercorarius antarcticus), elephant seals (Mirounga angustirostris), fur seals (Arctocephalinae), wandering albatross (Diomedea exulans) and Antarctic terns (Sterna paradiaea). In 2023, HPAI H5N1 was also detected in the Galápagos for the first time in red-footed boobies (Sula sula), frigate birds (Fregatidae), tropicbirds (Phaethontidae) , Nazca boobies (Sula granti), and blue-footed boobies (Sula nebouxii). Thus, the threat to global seabird populations is very real, and ultimately,
very concerning.
HPAI H5N1 has been documented to be affecting various species worldwide. In Canada, seabird mortalities are high, with the virus also being found to infect various mammalian species such as skunks, foxes, bears, and dolphins (Renaud et al., 2023). Across Europe, 21 countries have had documented outbreaks, largely clustered along coastlines (EFSA et al., 2023). European fur farms have been particularly affected by the outbreaks, and in the UK and South Africa, domestic poultry outbreaks are sporadic (Abolnik et al., 2024). Throughout South America, the virus has caused unprecedented deaths in wild birds, poultry and marine mammals (Tomas et al., 2024), with it being suggested that there may be transmission from mammal to mammal to seabird (Rimondi et al., 2024).
It is to be hoped that with conservation efforts, Bird Island can remain a unique sanctuary and that the populations may remain free from disease epidemics. There really is nowhere in the world like Bird Island, it is simply spectacular.
Gallery
References:
Abolnik, C., Roberts, L.C., Strydom, C., Snyman, A. and Roberts, D.G. (2024) ‘Outbreaks of H5N1 High Pathogenicity Avian Influenza in South Africa in 2023 Were Caused by Two Distinct Sub-Genotypes of Clade 2.3.4.4b Viruses’, Viruses, 16(6), pp. 896 Available at: 10.3390/v16060896.
EFSA, European Centre for Disease Prevention and Control, European Union Reference Laboratory for Avian Influenza, Adlhoch, C., Fusaro, A., Gonzales, J., Kuiken, T., Mirinaviciute, G., Niqueux, E., Staubach, C., Terregino, C., Baldinelli, F., Rusina, A. and Kohnle, L. (2023) ‘Avian influenza overview June–September 2023’, EFSA Journal, 21(10) Available at: https://doi.org/10.2903/j.efsa.2023.8328.
Feare, C. (2021) ‘Red-footed Boobies nest for the first time on Bird Island’, Wild Bird Conservation, -11-01T10:47:10+00:00. Available at: https://wildbirdconservation.wordpress.com/2021/11/01/red-footed-boobies-nest-for-the-first-time-on-bird-island/ (Accessed: Sep 10, 2024).
Feare, C. (2019) ‘Bird Island is not just for Sooty Terns!’, Wild Bird Conservation, -06-11T07:42:44+00:00. Available at: https://wildbirdconservation.wordpress.com/2019/06/11/bird-island-is-not-just-for-sooty-terns/ (Accessed: Sep 10, 2024).
Renaud, C., Osborn, A., Parmley, E.J., F Hatchette, T., LeBlanc, J., Weese, J.S., Misra, V., Yamamura, D., Forgie, S., Renwick, S., Webster, D. and Mubareka, S. (2023) ‘Highly pathogenic avian influenza: Unprecedented outbreaks in Canadian wildlife and domestic poultry’, Journal of the Association of Medical Microbiology and Infectious Disease Canada = Journal Officiel De l’Association Pour La Microbiologie Medicale Et L’infectiologie Canada, 8(3), pp. 187–191 Available at: 10.3138/jammi-2023-05-08.
Rimondi, A., Vanstreels, R.E.T., Olivera, V., Donini, A., Lauriente, M.M. and Uhart, M.M. (2024) ‘Highly Pathogenic Avian Influenza A(H5N1) Viruses from Multispecies Outbreak, Argentina, August 2023’, Emerging Infectious Diseases, 30(4), pp. 812–814 Available at: 10.3201/eid3004.231725.
Tomás, G., Marandino, A., Panzera, Y., Rodríguez, S., Wallau, G.L., Dezordi, F.Z., Pérez, R., Bassetti, L., Negro, R., Williman, J., Uriarte, V., Grazioli, F., Leizagoyen, C., Riverón, S., Coronel, J., Bello, S., Páez, E., Lima, M., Méndez, V. and Pérez, R. (2024) ‘Highly pathogenic avian influenza H5N1 virus infections in pinnipeds and seabirds in Uruguay: Implications for bird-mammal transmission in South America’, Virus Evolution, 10(1), pp. veae031 Available at: 10.1093/ve/veae031.
Trevail, A.M., Nicoll, M.A.C., Freeman, R., Corre, M.L., Schwarz, J., Jaeger, A., Bretagnolle, V., Calabrese, L., Feare, C., Lebarbenchon, C., Norris, K., Orlowski, S., Pinet, P., Plot, V., Rocamora, G., Shah, N. and Votier, S.C. (2023) ‘Tracking seabird migration in the tropical Indian Ocean reveals basin-scale conservation need’, Current Biology, 33(23), pp. 5247–5256.e4 Available at: 10.1016/j.cub.2023.10.060.