Ascension is a small island of volcanic origin and is found in the South Atlantic Ocean roughly midway between South America and Africa (7° 57’ S, 14° 22’ W) and forms part of the British Overseas Territory of St Helena, Ascension and Tristan da Cunha.
From a natural history perspective Ascension is a breeding site for the green turtle (Chelonia mydas) and a number of seabird species of which the Sooty Tern is the most numerous. Ascension played a key role as a staging post during the 1982 Falklands conflict and still provides the link between the UK and the South Atlantic.
Our Work on Ascension Island
British military ornithological societies have monitored the colony of Sooty Terns Onychoprion fuscatus and other seabirds on Ascension Island in the South Atlantic since 1987. The first population census was completed in 1990 ten years prior to the commencement of the RSPB cat eradication on the Island. Sooty Terns were closely monitored during the two years when cats were culled and now we continue the monitoring in the post eradication phase. The longitudinal study has focused on the breeding biology of the Sooty Tern and concentrates on establishing trends in the breeding population, identifying and recording levels of predation, site fidelity, sub-annual breeding, investigating nest and adult survival rates, and more recently to identifying their migration sites.
The long term monitoring programme on Ascension was not planned and there is no lead organisation dictating the direction of the project. The programme has evolved over time and the focus now is on publishing the information that has already been gathered, filling gaps in existing data sets and to continue with the monitoring work. Over the years the lead role has changed hands a number of times. The organisations involved are:
- The Royal Air Force Ornithological Society (RAFOS) which mounted the first expeditions in Feb 87 and Nov 88 and has contributed to most expeditions since.
- The Army Ornithological Society (AOS), the main contributor, mounting expeditions in 1990, 1991, 1994, 1996, 1998, 2000, 2002, 2004, 2005, 2006, 2007, 2008, 2009, 2011 and the most recent in 2012.
- The Royal Navy Bird Watching Society (RNBWS) which has contributed field workers, ringers and boat surveys.
The main aim of this long term monitoring programme is to facilitate the expansion of the breeding population by identifying and reducing threats to the Sooty Tern colonies. The following tasks are conducted:
- Surveys of the breeding population are undertaken at regular intervals.
- The levels of predation in the colony are measured and recorded.
- A ringing and re-trap programme is maintained so that inter and intra colony movements can be monitored and survival rates determined.
- Perceived threats to the colony are investigated.
- Long term, quantifiable data that can be used as evidence for making conservation management decisions on Sooty Terns is collected and made available to interested parties.
Ascension Island Overview Map (Imagery © 2009 DigitalGlobe)
Useful Ascension Island References
Birds of Ascension Island
Ascension Island is home to 15 species of bird, both native and non-native. This section provides a short introduction to 5 species and, over time, will be expanded to cover all 15. For those who wish to learn more there are downloadable information sheets which include further references and, where possible, these are linked to the relevant research papers.
Masked Booby (Sula dactylatra)
The Masked Booby is a large robust seabird 80 cm long, wing span 165 cm and weight 1.6 kg. They are the commonest of the three boobies in the genus Sula found on Ascension. Adults are white with the wing tips and trailing edge of the wing black, black tail, straw coloured feet and bill.
Sooty Tern (Onychoprion fuscatus)
Sooty Terns are graceful swallow-like birds with forked tail and slender, pointed wings. Adults, both male and female, are generally white underneath with black back. On the forehead there is a white patch which does not extend further back than the eye. The leading edge of the wing is white. The bill, legs and feet are black. The adult is a relatively large tern length 44 cm, wingspan 90 cm.
White Tern (Gygis alba)
The White Tern is relatively small tern (length 30 cm, wingspan 78 cm). Male and female adults have snow-white plumage. A narrow ring of black surrounds the orbit and emphasises the dark coloured eye. White Terns are inquisitive little birds, so it is not rare for walkers on the east part of Ascension Island to find White Terns hovering overhead, carrying out an inspection. In this situation, the wings of the tern are quite translucent, thus accentuating the overall delicacy of this graceful bird.
Brown Noddy (Anous stolidus)
Common Noddies, despite their name, are fairly rare around Ascension Island. The bird is similar in size to a Sooty Tern (length 42 cm, wingspan 83 cm). Their plumage is mainly dark brown with black tail and wing tips. The tail is wedge shaped with a shallow V indentation. Both sexes have similar colouration.
Common Mynah (Acridotheres tristis)
Common Mynas are 25–26 cm medium sized but heavily built starlings (Feare & Craig 1998). Mynas were introduced to Ascension from Mauritius in 1879. These birds are noisy and hop or walk with ease. The adults have dark brown backs with lighter brown bellies. The head and wing tips are black. There is a white patch on the upper and lower surface of the wing. The tail has a white tip. The bill, face patch and legs are yellow.
Trend in the population of Sooty Terns breeding on Ascension Island, South Atlantic
Reliable population estimates are essential for effective wildlife management and conservation. On Ascension Island trends in seabird populations are required to quantify the results of a feral cat eradication programme. A count of nests at the peak of their incubation period was the method adopted by the Army Ornithological Society (AOS) to census Ascension Island Sooty Terns. The total population is so large that censuses involved estimated mean Apparently Occupied Nests (AoNs) density in sample quadrats and extrapolated these to the estimated area of the colony.
Maps of the colony between 1990 and 2011 are available to view using a KML file loaded into Google Earth (see Ascension Island KML File For Google Earth ™ below).
Using geolocators to discover where Sooty Terns go between breeding seasons on Ascension Island in the South Atlantic
Geolocators are tiny archival tags that can be deployed on birds in order to collect location data. Such tags collect light data through a photo cell and this allows us to estimate the longitude and the latitude of the bird carrying the tag through timing of sunrise and day length, respectively. Tags need to be retrieved by researchers in order for data to be used in such remote sensing studies.
A variety of deformities (injuries, loss of leg etc) in the birds on Ascension were discovered during routine capture, handling and ringing of adults and chicks. Sooty Terns with their tongue protruding through their lower mandible were discovered in 2005.
The use of Google Earth imagery to identify seabird nests
Masked Boobies Sula dactylatra, like many other species of Sulidae, do not construct elaborate nests. However, their nest sites produce a characteristic ‘nest signature’. We found that these nest signatures could apparently be seen in freely available satellite images (Google Earth ™) of the main island of Ascension in the south Atlantic.
Ascension Island KML File For Google Earth - Maps of the Sooty Tern Colonies
This KML shows the extents of the sooty tern colonies for various years on both Mars Bay and Waterside. The KML also highlights the boundaries of the three study areas on the Ascension Islands (Mars Bay, Waterside & Letter Box). In addition to this the aerial farm between Mars Bay and Portland Point has been modelled to try and illustrate the dangers that the sooty terns face as they fly out to sea to feed.
Tools used: ESRI's ArcMap and Northgates' KML Editor
Open Google Earth file (407KB)
To get Google Earth go to the Google Earth download page
Age categories P1-P7 of Sooty Tern chicks
The images in this document show the age and plumage development of Sooty Tern chicks through the 7 age categories, P1 to P7.
Plasticity in breeding periodicity: the sub-annual cycle of Sooty Terns on Ascension Island
This poster gives a clear overview of the sub-annual breeding cycle of the Sooty terns on Ascension Island.
Sooty Tern Ringing Data
Sooty Tern (Onychoprion fuscata) ringing data is available for download as a compressed file (ZIP format - 1.35 Mb) and contains data files in Microsoft Excel (XLS) and Microsoft Access (MDB) formats.
Study Sites Interactive Map
Hughes BJ, Martin GR, Giles AD, Dickey RC & Reynolds SJ, 2015. Identification of an assembly site for migratory and tropical seabirds in the South Atlantic Ocean. Global Ecology and Conservation. TBC.
Seabirds are good indicators of wider biodiversity and where they assemble in large numbers signifies sites important to many marine faunal species. Few such large assemblage sites have been identified and none in pelagic waters has been identified in the tropical Atlantic Ocean despite their importance for resident seabirds and those ‘on passage’ during migration. Here, we identify the likely location of just such an assembly site and provide preliminary information about the distribution of pelagic seabirds around Ascension Island in the tropical South Atlantic Ocean using a combination of trans-equatorial seabird migrant tracking data, records of at-sea surveys and land counts of seabirds returning from foraging trips. We found that waters north–north-west of Ascension Island are used more often by seabirds than those south and east of the island. Three-fifths of the species recorded in the assembly site breed at mid- or high-latitudes and some of these migratory seabirds stopover possibly to wait for favourable winds that facilitate onward flight. Our findings are important because to the best of our knowledge no seabird assembly sites have previously been identified in tropical Atlantic Ocean pelagic waters. We provide evidence to support the aspirations of the Marine Reserves Coalition that waters in the vicinity of Ascension Island should be recognised as a sanctuary for marine wildlife and we highlight an area that is worthy of further targeted investigation.
Uncorrected proof to be published by Elsevier B.V. (open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)).Download
Hughes BJ, Martin GR & Reynolds SJ, 2012. Estimate of Sooty Tern Onychoprion fuscatus population size following cat eradication on Ascension Island, central Atlantic. Bulletin of the African Bird Club. 19: 166–171.
Feral cats, which had been depredating the population of Sooty Terns Onychoprion fuscatus on Ascension Island, were eradicated between 2002 and 2004. However, beneficial effects of this eradication with respect to the size of the breeding population have yet to be demonstrated. Census data have been gathered between 1990 and 2009, and we estimate that in 2010 the population comprised 414,000 birds. The duration of the breeding season was 193 days which is an increase of 30 days (or 18%) on the mean length of previous breeding seasons. There is an apparent increase in abundance of breeding birds but this was not statistically significant. Further censuses are imperative to characterise the population trend. There were anecdotal reports of numerous chicks fledging in 2010.
Hughes BJ, Martin GR & Reynolds SJ, 2011: The use of Google EarthTM satellite imagery to detect the nests of masked boobies Sula dactylatra. Wildlife Biology 17: 210-216.
Masked boobies Sula dactylatra, like many other species of Sulidae, do not construct elaborate nests. However, their nest sites produce a characteristic ’nest signature’. We found that these nest signatures could apparently be seen in freely available satellite images (Google EarthTM) of the main island of Ascension in the south Atlantic. We verified that this was the case by comparing nest signatures detected on these satellite images with field reports of occupied nests. We found that the locations of these nest signatures determined from satellite images agreed closely with the coordinates of actual nests on the ground. We used this information to determine the position and size of a previously unreported masked booby colony on the island. Thus, we show that the presence and abundance of some species can be estimated using freely available satellite imagery if a suitable signature in the satellite image can be found. Regularly updated satellite imagery of target sites could also be used for population monitoring. While this would be expensive, initial evaluation of the technique for particular species or populations can be achieved using freely available images. We encourage wildlife managers to view their study sites on Google EarthTM for evidence of their target species.
Bray A, Hughes BJ & Giles A, 2011. Sooty Terns on Ascension Island South Atlantic Integrated Population Monitoring Programme 24th Report. Unpublished Expedition Report, April 2011.
The expedition completed a full census of Sooty Terns. The colony size in early April 2011 was 181,000 AON [apparently occupied nests]. A further 2,526 sooty terns were ringed and 385 re-trapped. 20 Sooty Terns had geolocators fitted on metal rings on their legs which will require recovery next year. This will help us determine the movement of adults at sea between breeding periods. DNA samples were taken of Brown Noddies and White-tailed Tropic Birds. A survey of White Terns was taken across the whole island and stacks.
Hughes BJ, Martin GR & Reynolds SJ, 2010. Sooty Terns Onychoprion fuscatus on Ascension Island in the south Atlantic are a reproductively isolated population. Revista Brasileira de Ornitologia 18(3): 194-198.
Population size is determined by the balance of births and deaths, and of immigration and emigration. In order to investigate population dynamics of the Sooty Tern Onychoprion fuscatus population on Ascension Island in the south Atlantic, we focussed on the key component of immigration by measuring the proportions of philopatric and immigrant recruits to the breeding population. The Sooty Tern colony had expanded by 7% following the eradication of Feral Cats Felis silvestris in 2003. Between 1975 and 2002 potential recruits to the breeding colony were ringed as chicks on Ascension Island and in colonies elsewhere in the Atlantic. Searches for these birds as adults breeding on Ascension commenced in June 2002 and continued until December 2008. Of the 600 chicks ringed on Ascension, 36 (or 6%) were recruited into the breeding population and of the 9,482 ringed in other colonies, only one (0.01%) was found breeding on Ascension Island. A further investigation of morphometric measurements revealed that Sooty Terns on Ascension were significantly different from those from neighbouring colonies. The sample of birds from Ascension was drawn from a different population and is possibly of a previously unidentified, sub-species. We conclude that immigration to the breeding population on Ascension is minimal and that they are a reproductively isolated population.
Reynolds SJ, Martin GR, Wearn CP, Hughes BJ, 2009. Sub-lingual oral fistulas in Sooty Terns (Onychoprion fuscata). Journal of Ornithology 150: 691-696.
Sub-lingual oral fistulas are a condition first reported in New Zealand Stitchbirds (Notiomystis cincta) in which a lesion develops on the periphery of the mandible in the oral cavity and a fistula develops through which the tongue protrudes. We report that it arises in another species, the Sooty Tern (Onychoprion fuscata), breeding on Ascension Island in the south Atlantic. We discovered five adults with oral fistulas out of a total of 13,664 adults and chicks ringed during 11 breeding seasons over 13 years. Compared with other threats to the Ascension breeding population of over 180,000 pairs of Sooty Terns, we report that oral fistulas are a minor threat to colony stability, especially because afflicted birds were incubating eggs. Nevertheless, our findings suggest that further investigations of whether the condition is sex-linked, of its pathogenesis, and of its causation would augment our knowledge of the biology of Sooty Terns; such information might also have conservation implications for our understanding of the condition in endangered Stitchbirds. We call upon ornithologists to report oral fistulas in other species, because it would seem unlikely that these are the only two species predisposed to the condition.
Hughes BJ & Bray A, 2009. Sooty Terns on Ascension Integrated Population Monitoring Programme 23rd Report. Unpublished Expedition Report, October 2009.
The report for the expedition that was conducted over the period 7-20 October 2009 is not currently available.
Hughes BJ, 2009. Productivity of Sooty Terns on Ascension Integrated Population Monitoring Programme 22nd Report. Unpublished Expedition Report, January 2009.
The report for the expedition that was conducted over the period 21-27 January 2009 is not currently available.
Hughes BJ, Martin GR & Reynolds SJ, 2008. Cats and seabirds: Effects of feral Domestic Cat Felis silvestris catus eradication on the population of Sooty Terns Onychoprion fuscata on Ascension Island, South Atlantic. Ibis 150 (Suppl. 1), 122-131.
The population of Sooty Terns Onychoprion fuscata breeding on Ascension Island in the Atlantic Ocean was monitored over 17 years (1990-2007). This period spanned the programme of feral Domestic Cat Felis silvestris catus eradication from the island, which commenced in 2001 with the last Cat recorded in 2004. We report on the abundance of Sooty Terns and Black Rats Rattus rattus before and after Cat eradication. The Sooty Tern breeding population in the 1990s averaged 368 000 and Cats were killing Terns at an average rate of 33 adults per night. Following Cat eradication, adult Terns are no longer predated. However, egg predation by both Rats and Common Mynas Acridotheres tristis has continued with Mynas destroying more eggs than Rats. Unexpectedly, we observed a change in Rat predatory behaviour. Following Cat eradication, Rats have become a major predator of Sooty Tern chicks. Despite this change, the Tern population has shown a season-on-season increase since Cat eradication, 48.8% in 2005, 8.2% in 2006 and 6.1% in 2007, and the breeding population increased to 420 000 birds in 2007. Incubation success improved from 66.0 to 84.4% during Cat eradication, before dropping down again to 67.9% after Cats were eradicated and Rat control measures were introduced. Index traplines were set for Rats and Rat numbers fluctuated widely immediately after Cats were eradicated but there were no significant differences that could be attributed to changes in Cat numbers. Ascension Island Sooty Terns breed every 9.6 months and juveniles defer breeding for seven seasons. Hence 2008 is the first year in which an increase in the breeding Sooty Tern population directly attributable to Cat eradication is likely to be detected. We conclude that long-term monitoring is essential to guide conservation practice even in this relatively simple predator-prey system.
Hughes BJ & Wearn C, 2008. Sooty Terns on Ascension Integrated Population Monitoring Programme 21st Report. Unpublished Expedition Report, December 2008.
The report for the expedition that was conducted over the period 4-12 December 2008 is not currently available.
Hughes BJ & Bray A, 2008. Sooty Terns on Ascension Integrated Population Monitoring Programme 20th Report. Unpublished Expedition Report, February 2008.
The report for the expedition that was conducted over the period 7-20 February 2008 is not currently available.
Reynolds SJ, Martin GR, Wallace LL, Wearn CP & Hughes BJ, 2007. Sexing sooty terns on Ascension Island from morphometric measurements. Journal of Zoology 274, 2-8.
Sooty terns Onychoprion fuscata are one of the most abundant seabirds but breeding populations in many colonies have diminished. Rapid sexing of sooty terns in the field could be crucial in advancing our understanding of their reproductive biology, and in promoting conservation. However, sooty tern males and females are identical in their plumage and, thus, difficult to sex in the field. Morphometric measurements were taken from 63 adult sooty terns breeding on Ascension Island in 2005. A small blood sample was taken from the brachial vein to determine the bird's sex using standard PCR-based molecular techniques. Males were consistently larger in all morphometric measurements than females but considerable overlap between the sexes resulted in no single measurement being a useful discriminator of sex. A principal components analysis on a correlation matrix of seven morphometric measurements indicated that the first principal component (PC1) was a good 'body size' axis explaining 40.5% of the variance in the original matrix. The suite of head measurements all had high character loadings on PC1 and were, therefore, good indicators of the body size of sooty terns. Tarsus length and wing length were less reliable predictors of sex. Discriminant analyses revealed that a disciminant function incorporating head measurements and wing length allowed 77.8% of sooty terns to be sexed correctly based upon morphometric measurements alone. Further morphometric approaches to sexing should be explored with sooty terns captured in subsequent years.
Bray A. 2007. Ascension Island. Bulletin AOS 2007.
Our visit was just before the start of the 25th anniversary of the Falklands War. It was a member of the Army Ornithological Society (AOS), Major Peter Hubert the Force Reconnaissance Officer who compiled a report on the birds on Ascension which was published in our Bulletin in May 1982. These reports went to Birdlife International who then asked the British Armed Forces to carry on with a monitoring programme as so little information was known except for the odd expedition report.
Griffin R & Vincent M, 2007. Masked Booby Sula dactylatra nesting on Letterbox Ascension Island. Bulletin AOS 2007.
For over a hundred years Feral cats have prevented Mask Boobies from nesting successfully on Ascension Island. Following the eradication of the feral cats in 4004, Boobies have returned to Letter Box area of the main Island from the predatory free offshore islets. We report on the latest survey on the AOS study site on Letter Box.
Hughes BJ & Bray A, 2007. Sooty Terns on Ascension Integrated Population Monitoring Programme 19th Report. Unpublished Expedition Report, May 2007.
The report for the expedition that was conducted over the period 29 April - 24 May 2007 is not currently available.
Hughes BJ and Wearn C, 2006. Rat predation and survival rate of Sooty Tern chicks Supplement 1 to Rat monitoring on the Sooty Tern colonies of Ascension Island, South Atlantic. Report for the Ascension Island Government, April 2006.
The rat, namely Rattus rattus and probably Rattus norvegicus are now the principal predators of Sooty Terns Sterna fuscata on Ascension Island. During the October 2005 breeding season, less than three years after feral cats were eradicated, rats have filled this predatory niche. We used rat indices to determine the expansion in rat numbers. The Sooty Tern chick survival rate was determined from ring recoveries and by counting carcasses in sample quadrats. At Mars Bay the rat population has expanded five-fold and rats now take a higher number of chicks than were previously predated by cats. In the study area rats killed a minimum of 52% and possibly extending to 100% of the chicks. Monitoring of the rat population is crucial for managing this problem. If the colony is to survive extensive and continual rat control measures will be required.
Hughes BJ & Vincent M, 2006. Sooty Terns on Ascension Integrated Population Monitoring Programme 18th Report. Unpublished Expedition Report, August 2006.
The report for the expedition that was conducted over the period 6-18 August 2006 is not currently available.
Feare C, 2006. Notes following a visit to Ascension Island. Unpublished Report.
This report is not currently available.
Bray A, 2006. Ascension Feb 06. Bulletin AOS 2006.
The disruption to our expedition in October 2005 meant that some work was not finished. We wanted to finish the land bird survey so a quick trip was organised in early February 2006. Team members were Andrew Bray, Roger Dickey, David Vaughan and Christopher Dickey. On arrival in Ascension we managed to see the last handful of the Sooty Tern juveniles at Waterside that were about to leave. There were also several pairs of Brown Noddies nesting in the area.
Hughes BJ, 2005. Non-native species and threats to Ascension Sooty Terns. UK Overseas Territories Conservation Forum - Forum News 28: 3.
Despite the eradication of Feral Cat Felis catus predation on Sooty Terns Sterna fuscata by non native species continues. Many exotics were introduced to the island during the last 150 years but only recently was the damage they caused recognised, goats were the first vertebrate to be removed followed by cats in 2004.
Hughes BJ & Wearn C, 2005. Longevity of Sooty Terns Sterna fuscata on Ascension Island. Atlantic Seabirds 7: 42-43.
In June 2002 and April 2003, while carrying out fieldwork on Ascension Island in the South Atlantic, ringed Sooty Tern Sterna fuscata were captured bearing American ring numbers 1013 13651 and 1013 13584 respectively. Records from the Bird Banding Laboratory at Patuxent established the banding was undertaken in niovember 1975 aging the individuals at 26½ and 27½ years respectively. Terns are long lived birds and the oldest tern recorded is a Sooty Tern aged 36 years (Schreiber & Burger 2002). The oldest known breeder on the Seychelles is 34 years old, on Dry Tortugas 32 years, and in the Pacific 26½ years (Schreiber et al. 2002). The previous longevity records for Sooty Terns on Ascension were 16½ years on 7 July 1942 and 18 years in March 1944 (Thacher Cooke 1945). Our ring recoveries suggest that despite feral cat predation on Ascension, Sooty Terns in the South Atlantic live as long as other Sooty Terns in the Pacific, Indian and North Atlantic Oceans.
Hughes BJ & Bray A, 2005. Sooty Terns on Ascension Island South Atlantic Integrated Population Monitoring Programme 16th Report. Unpublished Expedition Report, November 2005.
The expedition completed a full census of the Sooty Terns Sterna fuscata. The colony size at the end of October 2005 was 183,000 AON [apparently occupied nests]. Predatory activities on our three study sites were recorded. Rat numbers have increased significantly and high levels of rat predation (35 rats per 100 trap nights) were measured. A further 2,000 sooty terns were ringed and 116 re-trapped. DNA and biometric measurements were taken from 66 ringed birds. The DNA was used to sex the terns and a paper on sexing sooty tern from biometrics is being prepared. Sooty terns that were feeding large chicks were trapped and ringed, with green colour rings, with the aim of re-trapping the birds next season so as to determine the length of the breeding cycle.
Hughes BJ and Wearn C, 2005. Rat monitoring on the Sooty Tern colonies of Ascension Island South Atlantic. Report for the Ascension Island Government, November 2005.
The Black Rat Rattus rattus is now a serious predator of Sooty Tern Sterna fuscata on Ascension Island. Predation is patchy but it occurs on both of the main sub-colonies on the island. We have insufficient data to ascertain if the losses due to rat predation are large enough to threaten the survival of the colony. However, there is an urgent need to develop contingency plans for reducing the rat population on the seabird colonies at Mars Bay and Waterside. Continual monitoring of the threat is essential. Until recently, rat predation on Sooty Terns has been negligible. A half century ago the British Ornithologists’ Union Centenary Expedition found no evidence of predation. Service ornithological societies have monitored predation by alien species on the Sooty Tern population of Ascension for more than 20 years and only recently have we recorded rat predation. During the years1982 to 2002, despite the fact that we spent over 1,000 man-days monitoring the colony, we never saw a rat, live or dead, on our study sites. We have used night vision goggles to monitor the colony after dark, but again no rats were seen. Today the picture is quite different. The two large colonies of Sooty Terns on Ascension are littered with highly visible poison bait stations, rat corpses can easily be found in the colonies, egg predation is widespread and some of this can be attributed to rat predation. The most telling evidence of rat predation is freshly killed juvenile Sooty Terns with small segments of the back muscles missing. Our ringing and trapping programmes have revealed a rapid increase in the numbers of rats in the colonies and a major increase in the level of rat predation. In this report we have documented the evidence we have collected from the most recent expedition and added it to the evidence we collected in June 2002, April 2003, February 2004 and November 2004. While visiting Ascension in October 2005 we monitored rats on our three study sites. We completed rat indices at these three locations and investigated predation by rats in the Sooty Tern colonies. We found no evidence of rats on the Letterbox site. On the Waterside and Mars Bay sites we found significant but localised populations of rats predating on Sooty Tern eggs and juvenile birds. We examined corpses of dead terns but found no evidence that rats were predating the adult Sooty Terns. We marked eggs and ringed chicks and monitored their survival rates. Egg survival rate at 8% was lower than all but one of the previous seasons. Rats destroyed 20,000 eggs this season. The rats found in one colony at Mars Bay are considerably larger than the Black Rats previously trapped. These rats were responsible for the heavy predation found on the site. Of the 200 chicks that we ringed on a sub-colony at Mars Bay, 38 chicks were found dead less than 2 weeks after they were ringed and after eight weeks, a total of 102 chicks were found dead. Rats predated over half of the chicks ringed in this area. There is no doubt that rats are the cause of this high mortality as chicks that were killed shortly before they were found showed clear evidence of rat predation. The local rat index at this location was the highest we have recorded at 34.5 rats per 100 trap nights.
Hughes BJ & Wearn C, 2004. Sooty Terns on Ascension Island South Atlantic Integrated Population Monitoring Programme 15th Report. Unpublished Expedition Report, December 2004.
The expedition completed a full census of the Sooty Terns. The colony size on 30 Nov 04 was 123,000 AON [apparently occupied nests]. Predatory activities on our three study sites were recorded. A further 500 Sooty Terns were ringed and 162 were re-trapped.
Hughes BJ, 2004. Conservation Value of Mars Bay Ascension Island. Report for the Ascension Island Government, March 2004.
Mars Bay is a small distinct area of scientific interest for flora, invertebrates and physiographical features. Despite having been recently declared a nature reserve no appraisal of its conservation value has been undertaken. This paper attempts to rectify this omission and to propose the next steps to secure the future of this site. Mars Bay is situated on the northwest corner of Ascension a tropical island 8º south and 14º west in the South Atlantic (Fig 1). The site is relatively unknown and has no history of conservation action until recently. At first glance it would appear to have little conservation value as it is devoid of indigenous mammals and the home of just one species of sea bird. Yet hidden away on the site are small pockets of endemic plants and creatures that are of immense interest and of international importance. [Report less Figures and Maps]
Hughes BJ & Bray A, 2004. Sooty Terns on Ascension Island South Atlantic Integrated Population Monitoring Programme 14th Report. Unpublished Expedition Report, February 2004.
The expedition was on Ascension Island from 8-28 Feb 2004. The team consisting of ten members completed a full census of the Sooty Terns. The colony size on 24 Feb 04 was 169,370 pairs (LCI = 160277; UCI = 178583). Predatory activities on our three study sites were recorded, no evidence of predation by feral cats was found. A further 2000 Sooty Terns were ringed and 163 were re-trapped. The team provided ringing training to members of the Ascension Island Conservation Office and a ringing policy for the Island was formulated. Studies of Sooty Terns ariel [sic] drinking and dipping were carried out and also the activities of the birds at night were recorded. A population survey of Fairy Terns and land-birds was completed. Clear evidence of attempts by eight pairs of Brown Noddy to breed in the Sooty Tern colony on the mainland was recorded. Guano deposits from Letterbox and DNA samples from three more avian species were collected. A list of data based [sic] maintained by Service Ornithological societies was compiled.
Hughes BJ, 2003. Sooty Terns on Ascension Island South Atlantic Integrated Population Monitoring Programme 13th Report. Unpublished Expedition Report, May 2003.
The population survey this season was carried out at the optimum time for maximum numbers and for direct comparison with previous seasons. The colony on Ascension is at its greatest 42-60 days after the first egg of the season is laid.
Hughes BJ, 2001. Sooty Terns on Ascension Island South Atlantic Integrated Population Monitoring Programme 11th Report. Unpublished Expedition Report, September 2001.
Monitoring and surveys at the Sooty Tern Sterna fuscata breeding colony in September 2001 was undertaken by B. John Hughes a member of the RSPB Ascension Island expedition and also a member of the Army Ornithological Society (AOS). The aim of the expedition was to maintain the baseline surveys of seabirds prior to the eradication of cats. A census was completed of the Ascension Island Frigate Bird Fregata aquila and the three species of Booby Sulidae found on Boatswain Bird Islet and 14 offshore stacks details are at Annex A. A census was also completed of the tiny Sooty Terns colony on Boatswain Bird Islet and the two large colonies at Mars Bay and Waterside on the south west corner of the island. This report is focused on the baseline survey of Sooty Terns.
Dickey RC, 2000. Exercise Booby VII Recce Report. Unpublished Recce Report, January 2000.
The aim of the recce [reconnaissance] was to ascertain the status of the Sooty Tern breeding colonies, by observation and by photography, in order to determine the optimum expedition dates for Nov/Dec 00.
Ratcliffe N, Hughes BJ & Roberts FA, 1999. The population status of Sooty Terns Sterna fuscata on Ascension Island. Atlantic Seabirds 1(4): 159-168.
Feral cats were introduced to Ascension Island in the 1800s and extirpated all seabirds with the exception of Sooty Terns to inaccessible islets, stacks and cliffs. Sooty Terns continue to breed in reduced numbers on the south-west plains of the island and are still subject to cat predation, so monitoring of their population trends is important. Measuring the impact of cat predation upon seabird populations depends on having reliable baseline data; censuses of Sooty Terns on Ascension were conducted in 1990, 1996, 1997 and 1998 and involved sampling clutch densities in sub-colonies and then extrapolating to the total colony area. The population varied significantly over the study period, with 176000 pairs in 1990, 202000 pairs in 1996, 151 000 pairs in 1997 and 207000 pairs in 1998. The 22% reduction in 1997 compared with 1996 and 1998 is thought to be due to a large proportion of mature birds deferring breeding because of reduced food availability induced by oceanographic perturbations. Such variability in breeding population size in relation to stochastic events means that censuses need to be undertaken frequently to ensure trends can be detected with confidence.
Hughes BJ, 1999. The Status of the Sooty Tern (Sterna fuscata) on Ascension Island, South Atlantic. The Adjutant, Journal of the Army Ornithological Society, Vol 28: 4-13.
One of the main aims of the Army Ornithological Society (AOS) during the last decade [1990s] was to establish the breeding population of Sooty Terns on Ascension Island. To this end five expeditions were mounted and carried out surveys on the Island in 1990, 1992, 1994, 1996 and 1998. Three of the expeditions completed full surveys of the Sooty Terns at the height of their breeding season. The colony size was measured on each occasion and clutch densities in sample quadrats recorded. The size of the colony varied from 13.5 ha in 1990 to 9.87 in 1996 and 10.33 ha in 1998. A total of 1,105 clutch density samples were measured. An analysis of all the field data was carried out by Dr Norman Radcliffe at the RSPB. The population of breeding pairs of Sooty Terns in 1990 was 176,000 with a 95% confidence level of 21,000, in 1996 the population was 202,000 with a 95% confidence level of 14,000 and in 1998 the population was 207,000 with a 95% confidence level of 12,000. The precision of the survey and the reliability of the population figure increased over the period of 8 years and 11 breeding cycles. The combination of the three surveys provide a reliable population estimate and a firm base line for future census. The aim of the society, to establish the breeding population of Sooty Terns on Ascension Island, has been achieved.
Dickey RC, 1997. Exercise Booby V General Information. The Adjutant, Journal of the Army Ornithological Society, Vol 26: 4-9.
Ascension Island, situated approximately 80 south of the Equator, 1540 km south of Liberia and midway between South America and Africa, has been visited now by five Ex BOOBY ornithological expeditions, the last being in Apr 94. The aims of the expeditions have been consistent; to continue to monitor the status of breeding seabirds and land birds on Ascension Island with particular attention being paid to that of the Sooty Terns Sterna fuscato which has seen significant decline in the last century. Additional studies on Ex BOOBY V included predation on the Sooty Tern colonies, a report of breeding bird distribution on the Letterbox feature, blood sample collection for DNA analysis and biometric data collection combined with the ringing of breeding birds, particularly Sooty Terns.
The aims of the AOS expeditions to Ascension Island in 1992 and 1994 was to replicate the breeding survey of March 1990 at the same stage in the breeding cycle so as to permit a valid comparison. This has now been achieved. The population sizes are similar, the latest count shows a small increase (11% ) in the number of birds. The adult breeding population of Sooty Terns on Ascension Island in November 1996 was 388,000.
Hughes BJ, 1997. Blood Samples for DNA Analysis of Avifauna on Ascension. The Adjutant, Journal of the Army Ornithological Society, Vol 26: 17-20.
The Army Ornithological Society (AOS) expedition to Ascension Island in November 1996 collected blood samples for DNA analysis from about half of the species of sea and land birds that occupy the Island. Most of the birds breed in reproductive isolation and are ideal targets for studies using DNA techniques. Samples collected by the expedition are the only known samples taken from birds on the island and were forwarded to the Zoology Museum, University of Copenhagen to add to their world wide DNA data base. The information in this data base is freely available to all and can be viewed via the Internet. In total 57 samples were taken from nine different species including the endemic Frigate Birds Fregata aquila. This report describes the field procedures used to capture the birds and the techniques used to obtain the specimen. Samples were taken from live birds which were rung and then released.
Etheridge C, 1997. Letterbox Breeding Survey Report. The Adjutant, Journal of the Army Ornithological Society, Vol 26: 22-23.
One of the aims of the Ex BOOBY V expedition to Ascension was to observe and record seabird activity around the Letterbox feature and especially to look for breeding and roosting sites of seabirds. Letterbox is the most easterly part of Ascension and forms a remote circular projection from the main island. Its close proximity to the densely populated Boatswain Bird Island (BBI) marks Letterbox as one of the most likely on-shore areas where seabirds may still breed. The only seabird species that still breeds in any number of the main island is the Sooty Tern in the south western part of the island. Along the northern edge of Letterbox are steep cliffs some 400 feet high. Across the top, the surface of ash and lava is relatively flat and slopes southwards to the eastern and southern shores. As in many other parts of Ascension, breeding seabirds on Letterbox have suffered badly from the introduction of cats and rats. A more detailed AOS Letterbox report has been prepared by Hughes and Walmsley (1992).
Hughes BJ, 1994. Exercise Booby IV Introduction. In Hughes BJ, Thompson RG, Walmsley JG & Varley MJ, 1994. The Adjutant, Journal of the Army Ornithological Society, Vol 24: 4-24.
Ascension Island is situated approximately eight degrees south of the equator in the middle of the Atlantic Ocean. The Army Ornithological Society's (AOS) expedition Exercise Booby IV visited the island in April 1994. The aims were to continue the monitoring programme of the breeding seabirds and land-birds on Ascension Island. Particular attention was given to the Sooty Tern breeding population which formally had up to one million birds, but had declined to 350,000 in 1990. Subsequent breeding attempts have been catastrophic and the number of breeding birds is below 100,000. Predation by feral cats on Sooty Terns was monitored and a land bird survey carried out.
Hughes BJ, 1994. The 1994 Sooty Terns Breeding Season. In Hughes BJ, Thompson RG, Walmsley JG & Varley MJ, 1994. The Adjutant, Journal of the Army Ornithological Society, Vol 24: 4-24.
Sooty Terns (Wideawakes) Sterna fuscata return to Ascension every 9.6 months to breed. Their numbers on the island at anyone time vary greatly and for three months in every nine the entire population is absent. The maximum numbers occur on the Island approximately 6 weeks after the first egg of the season is laid (Ashmole 1963). The expedition had planned its arrival to coincide with this peak of breeding terns so that a valid census could be obtained. On the morning of 13 Apr the expedition recorded 200 terns on the ground in one of their traditional nesting sites; by late afternoon this number had risen to 2000. The first eggs of the season were laid on the Waterside Fairs or colonies on 18 Apr. A census of breeding Sooty Terns was carried out on 28 Apr by Hughes and Walmsley. This was only 10 days after the first eggs were laid and some 32 days before the date of maximum occupation of nest sites.
Hughes BJ, 1994. Sea-Watch Data. In Hughes BJ, Thompson RG, Walmsley JG & Varley MJ, 1994. The Adjutant, Journal of the Army Ornithological Society, Vol 24: 4-24.
All Service ornithological expeditions to Ascension have carried out sea-watches but to date no summary of them has been published. Table 3 is a record of the 22 hours of sea - watches produced by the expeditions in 1988, 1990 and 1992. The original field sheets contained a few notes in the remarks column on movements of Red-footed Bobbies. These notes were extracted and compiled into a report on this species (Nash et al.1992). None of the other data has been used. One of the aims of these sea-watches, was to look for vagrants but none were seen. The watchers however recorded the direction, movement and numbers of seven indigenous seabird species, namely the Black and Brown Noddy, the Brown and Masked Booby, White and Sooty Tern and the Ascension Frigate Bird. The majority of records show the numbers of birds passing during intervals of 5 minutes. Most of the watches took place at either dawn or dusk.
Morrison DM & Thompson RG, 1994. Seabird populations on the stacks of Ascension Island. In Hughes BJ, Thompson RG, Walmsley JG & Varley MJ, 1994. The Adjutant, Journal of the Army Ornithological Society, Vol 24: 4-24.
There are 15 stacks around the coastline of the island usable by seabirds. The lack of safe nesting and roosting places on the mainland, and the overcrowding on Boatswain Bird Island, make the smaller stacks important to the birds. This is reflected by the fact that in December 1993 the stacks were given SSSI status.
Walmsley JG, 1994. Predation by feral cats on the Sooty Terns. In Hughes BJ, Thompson RG, Walmsley JG & Varley MJ, 1994. The Adjutant, Journal of the Army Ornithological Society, Vol 24: 4-24.
The seabirds of Ascension Island have been subjected to predation by feral cats for more than 150 years. During this time ten of the eleven breeding seabird species have ceased to breed on the main island and are now confined to the off - shore Boatswain Bird Island and small inshore rocky stacks and cliffs. The exception is the Sooty Tern Sterna fuscata, which continues to breed on the broken lava and clinker in the south-west part of the main island.
Varley MJ & Dickey RC, 1994. Land-birds survey. In Hughes BJ, Thompson RG, Walmsley JG & Varley MJ, 1994. The Adjutant, Journal of the Army Ornithological Society, Vol 24: 4-24.
One of the aims of Ex Booby IV was to carry out a survey of land-birds. There are only five resident species and only three occur in any numbers. The least numerous are Red- throated Francolin Ptemistes afer and House Sparrow Passer domesticus. The more numerous were Indian Mynah, Acridotheres tristis, Canary Serinus flaviventris and Waxbill Estrilda astrild. The aim of the survey was twofold, firstly to ascertain the distribution of all land-bird species on the island and secondly to attempt to estimate the number present.
Hughes BJ & Walmsley JG, 1992. Surveying a line for a cat-proof fence on Letterbox, Ascension Island, South Atlantic. Unpublished Reconnaissance Report.
Report details not currently available.
Thompson RG, 1992. Exercise Booby III - Ascension Island 30 Jun - 7 Jul 92. Bull ABWS 2/92 2.
The nine members of the expedition Exercise Booby III gathered together at Brize Norton on 29 June prior to the departure for Ascension on an RAF Tristar.
Hughes BJ, 1992. The Sooty Terns of Ascension Island Sep 91 - Mar 92. The Adjutant, Journal of the Army Ornithological Society, Vol 22: 17-25.
Sooty Terns (Wideawakes) are the only sea birds that breed in any numbers on the main Island of Ascension. Their status in the past has caused some concern (Nash 1991). These concerns have been heightened by new fears arising from a poor breeding season during the period Sep 91 - Mar 92.
Hughes BJ, 1992. The Red-footed Booby Sula sula of Ascension Island. The Adjutant, Journal of the Army Ornithological Society, Vol 22: 21-24
The Royal Air Force Ornithological Society team led by Sqn Ldr Mike Blair was the first of these expeditions to visit the Island. The next was the Army Ornithological Society with Ex Booby I in November 1988, followed by Ex Booby II in March 1990 and the latest expedition Ex Booby III in July 1992, all under the leadership of Maj Hilary Nash. The data on Red -footed Boobies recorded by each expedition was small but when combined they are sufficient to give a good picture of the current status of the species. 144 separate sightings of Red-footed Boobies were recorded by over 21 different individuals. There can be no doubt that a small group of Red-footed Boobies still survives on Ascension Island.
Hughes BJ & Walmsley JG, 1992. Reconnaissance for a Cat-Proof Fence on Letterbox- Summary. The Adjutant, Journal of the Army Ornithological Society, Vol. 22: 25-30.
Cats were first introduced to Ascension Island in 1815 to control the increasing number of rats Rattus rattus. At that time there were reports of large breeding populations of seabirds: Boobies, Frigate Birds, Tropic Birds, Noddies and Terns. The cats were largely responsible for the decline and destruction of the mainland seabird colonies. Today the only indication which bears witness to the former wealth of seabirds on Ascension are large areas of guano and phosphate deposits in many parts of the Island and a declining Sooty Tern population, confined to the south -western part of the Island.
Nash RHJ, 1992. Report on the Census on Boatswain Bird Island. The Adjutant, Journal of the Army Ornithological Society, Vol 22: 30-40.
Exercise BOOBY III visited Ascension Island from 30 June to 7 July 1992. The Expedition was granted permission to land a party of three people on Boatswain Bird Island (BBI) for two nights in order to survey the breeding birds. This visit was made from 3 to 5 July. This report covers the observations made during those three days.
Walmsley JG, 1992. Feral Cat Predation on the Sooty Terns Sterna fuscata. The Adjutant, Journal of the Army Ornithological Society, Vol 22.
The onset of the Night Club activities confirms the presence of important number of feral cats on the breeding grounds. Daily collections of terns killed by feral cats in sample areas also show that the time has come when a more intensive and thorough control of the cat population, particularly in the breeding areas, is necessary if we are to save this important population from destruction.
Nash RHJ, Hughes BJ and Walmsley JG, 1991. Exercise Booby II ABWS Expedition to Ascension Island March 1990. The Adjutant, Journal of the Army Ornithological Society, Vol 21: 4-9 & 17-25.
Exercise BOOBY II was an ABWS sponsored expedition to Ascension. It was the third in a series of tri-service ornithological expeditions to assess the status of the breeding birds of Ascension Island. The expedition had 10 members, 7 from the Army, one from the Navy and two civilians, one from the ABWS and the other from RAFOS. Whilst on the Islands, the team was joined by Dr Philip Ashmole, Dr Myrtle Ashmole and Dr Ken Simmons, all professional zoologists, two of whom have spent a considerable period of time studying the Ascension birds.
Hughes BJ, 1991. Mapping the Sooty Terns. In Nash RHJ, Hughes BJ and Walmsley JG, 1991. Exercise Booby II ABWS Expedition to Ascension Island March 1990. The Adjutant, Journal of the Army Ornithological Society, Vol 21: 4-25.
The status of Wideawakes or Sooty Terns, Sterna fuscata on Ascension Island has never been accurately determined. In the eighteenth and nineteenth centuries vast numbers nested on the island and in this century estimates of their numbers have ranged from 750,000 in 1957 -59 (Ashmole, 1963) to 100,000 in 1987 (RAFOS).
This paper is concerned entirely with the mapping aspects of the census. Each colony on the island was surveyed, its area determined and its outline accurately drawn on a map. Sample density counts were conducted under the guidance of Dr N.P.Ashmole and were used to determine the estimated number of eggs in each fair.
Walmsley JG, 1991. Feral cat predation on Sooty Terns on Ascension Island. In Nash RHJ, Hughes BJ and Walmsley JG, 1991. Exercise Booby II ABWS Expedition to Ascension Island March 1990. The Adjutant, Journal of the Army Ornithological Society, Vol 21: 4-25.
Feral cats, Felis catus have been known to prey upon the breeding seabirds of Ascension Island for over 170 years. During this time they have succeeded in eliminating all breeding seabirds, with the exception of the Sooty Tern Sterna fuscata, and five species of land birds. All other seabirds are confined to the small offshore Boatswain Bird Island, 300 metres from the main island off the south east coast, and to inaccessible cliffs and offshore stacks. The number of feral cats on the island is unknown, but one cat to every thousand Sooty Terns was a figure put forward by Ashmole (1963).
During the limited time we spent on Ascension, quantitative data was collected on predation by cats on adult terns, up until the time the chicks hatched. This period represents the "night club" activities, the onset of egg -laying, and the establishing of breeding colonies or "fairs". Complementary information on cat kills was obtained from Mars Bay and Big John fairs up to the time of our departure.
Hortop J, 1989. Exercise Booby. Bull ABWS 1/89.
Why, however, was the RAF Ornithological Society (RAFOS) mounting an expedition to Ascension Island and why were there two pongos in the party? Whilst in Military terms the Island is significant in being a staging post, in ornithological terms it is valued for its massive sea bird colonies which assume international importance for many of the resident species. No formal survey of the Island had been carried out since the Storehouse British Ornithological Union (SOU) 18 month expedition in 1958/59.
The MOD Conservation Officer and ornithological societies of the 3 Services have been encouraged by international civilian bodies to mount a series of expeditions to re-establish census base lines following the increase in disturbance during and after the Falklands conflict.
Osborn D, 1994. The Royal Air Force Ornithological Society Expedition to Ascension Island 15-30 November 1988. The Royal Air Force Ornithological Society Journal 23: 19-29.
The RAFOS mounted an expedition to Ascension Island, from 15-30 November 1988, following a similar RAFOS expedition in February 1987, (see 1987 Report in RAFOS Journal No 19). The MOD Conservation Officer and the ornithological societies of the 3 Services had been encouraged by civilian organisations to monitor levels of change to the seabird colonies at this important site, after the influx of personnel during the Falklands crisis in 1982. These expeditions continue the trend of the military ornithological societies carrying out internationally important bird studies, wherever possible.
Blair M, 1989. The RAFOS Expedition to Ascension Island 1987. The Royal Air Force Ornithological Society Journal 19: 1-35.
A team of eight RAFOS members took part in an expedition to Ascension Island in the period 9-25 February 1987. The island lies approximately 7.5 deg south of the Equator and 14.25 deg west of the Greenwich meridian. The nearest land is St. Helena, 1100km south east. Nigeria lies 1460km north and the Congo and Brazil are approximately equidistant to the east and west respectively at approximately 1750km. The International Council for Bird Preservation (ICBP) has expressed considerable interest in the status of the endemic Ascension Frigatebird (Fregata aquila).
Hubert PJ, 1982. Ascension Island - Feb 1982. Bulletin Army Ornithological Society, 2/82 E.
However it is the sea-birds that are the main source of interest. At present only the Wideawake Terns breed in large numbers on Ascension Island. The main breeding grounds for the remaining ten species is an islet off the South East corner –Boatswain Bird Island, a 300 foot high lump of lava about 200 yards off shore, and looking rather like a white Christmas cake.