Seabird News

Seabird News SEYCHELLES SEABIRD GROUP Newsletter Issue 5 Nov 2009

The Seychelles Seabird Group was formed in 2002 to facilitate the sustainable management and conservation of seabird resources in Seychelles. It comprises owners and managers of globally recognized IBAs (Important Bird Areas) and nationally important seabird sites. Our main role is to work collaboratively to: Gain national perspective; Prioritise seabird research and monitoring on a national level; Coordinate all seabird research and monitoring; Utilise standardised methods to ensure the comparability of data; Ensure priority seabird work is undertaken; and Use information collected to direct future research and/or management.

Produced by:

For the SSG. For more information please contact: Gilles-David Derand, Seabird Group Coordinator, Nature Seychelles, Centre for Environment and Education, Roche Caiman, Mahé, Seychelles. ph: +248 601100 fax: +248 601102 email: david@natureseychelles.org

Inside: News from members Articles: Substitute Nest Provision for Fairy Terns (Gygis alba) on Cousine Island Extending Seychelles Important Bird Areas (IBAs) to the marine realm Seabirds as bio-indicators in the Western Indian Ocean The secret lives of shearwaters Effects of Pisonia grandis on seabirds Caspian Terns on Aldabra Atoll

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Hello again, Seychelles Seabird Group Dear SSG members, It is a great pleasure for me to contribute to the revival the Seychelles Seabirds Group newsletter, which has been quite dormant since the last edition, number 4 published in May 2006. Maybe one should recognize that the aims of the Seychelles Seabirds Group and SSG newsletter initially launched on 23rd April 2002, were probably very ambitious, given the different status and management bodies of the islands involved. Thus the initial willingness to gain a national perspective and prioritise seabird research and monitoring on a national level, notably through unique monitoring protocols and a shared seabird database, was apparently out of reach.

However, I believe there is still room for inter-islands collaboration and useful exchanges of experience on seabirds’ research and monitoring, as proved by the last two SSG meetings held in November 2008 and May 2009.

Therefore, this newsletter intends to build up once more the link between

the individual managers, island owners and seabirds researchers working in Seychelles, as demonstrated by the article on the impact of Pisonia grandis on seabirds, a subject that has important practical implications in terms of habitat management for the inner granitic islands, especially for Aride and Cousin.

This newsletter also intends to fill the gap in the dissemination and sharing of seabirds research results conducted in Seychelles by external scientists.

Thus, you will find enclosed updated information regarding the long-term survey of seabird breeding parameters conducted by ECOMAR/University of Reunion island since 2005 on Cousin, as well as insights into innovative projects using seabird tracking (geolocators) on Cousin and D’Arros to investigate wedge-tailed shearwaters foraging ecology and expected to help define marine Important Bird Areas (MIBAS) for Seychelles. Wish you all a good reading!

Gilles-David Derand, Nature Seychelles science coordinator & SSG coordinator

Data and information contained in this newsletter is the property of the authors or institutions they work for. Please contact the SSG coordinator if you wish to use or quote information contained herein.

Seabird News Issue 5, November 2009

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2009 seabirds news from Bird Island

News:

Jo Savy

Sooty tern on Bird Island © Dao Nguyen/Nature Seychelles

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’m very relieved to report that this year has been a good year for the Sooty Tern colony. Despite my worries that we might experience another terrible season like last year, thankfully it never happened. The South East winds have been constant and have obviously brought the food which the Sooties rely on.

We have not experienced high chick mortality as in previous years and as usual we cropped eggs from half of the colony for sale locally.

The formula seems to be a winning one, maintaining a healthy sized colony and raising income for further conservation work on the island whilst ensuring that we

can still operate a hotel on the island without an encroaching bird colony or disturbance to clients’ enjoyment of the island. Terrence Valentin joined us from the Ministry of Environment to oversee the cropping programme for the months of June and July and to help in our yearly task of ring searching. We found a good number of ringed birds and will be sending the data off to Chris Feare for analysis since he was unable to make the trip to Bird this year due to our closure.

Our Lesser Noddy Tern population is thriving and the Common Noddies, Fairy Terns and White Tailed Tropic Birds remain stable. At the end of March, White-tailed tropicbirds occupied 42 nests with 8 eggs being incubated and 7 chicks present. Our familiar visitor, a solitary Brown Booby who displays

unsociable behaviour by choosing to stay alone at the southern end of the island is back with us since August as is the beautiful Pacific Golden Plover who arrived about a week ago – it is almost certainly the same individual as seen in previous years as it stays in the same area between the chalets and the water tower.

Migrant Count for August Eurasian Curlew 1 Common Sandpiper 1 Grey Plovers 5-6 Whimbrels 10-18 Ruddy Turnstones 10-20 Crested Terns 5-6 Lesser Sandplovers 2-3 Greater Sandplovers 3-5 Crab Plover 1 Red Footed Boobies 1-8 Frigates 85-125 (mostly lesser and younger individuals plus a few greater males)

Seabird News From Cousine Island

By Kevin and San-Marie Jolliffe

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ince January 2006, Cousine Island has seen a number of interesting changes taking place, with the complete rehabilitation of the severely degraded plateau area and the successful planting of the natural forest. The forest has matured very well and now provides valuable nesting sites for the increasing numbers of Lesser Noddies.

Seabird monitoring The monitoring of a number of seabird species has been ongoing since 1992, notably for White-tailed tropicbirds and Lesser Noddies. The methodologies used are drawn from the Seabird Monitoring Handbook for Seychelles (Burger and Lawrence, 2003). Some species such as the White-tailed Tropicbird are monitored throughout the year, while other seasonal breeders like the Lesser Noddy are only monitored during the breeding season.

White-tailed tropicbird monitoring During 2009, a number of nests were removed from the list, after not being occupied for a number of years and additional nests were added to bring the total back up to 100 nests. As the Tropicbirds breed throughout the year, it has been revealed that only a third of the nests are occupied at any one time, which influences the overall seabird census conducted during Lesser 2

Seabird News Issue 5, November 2009

White tailed Tropicbird on Cousine Island

and Brown Noddies main breeding season. A total of 126 birds were also rung, 75 of which were adults and 51 were C3 chicks.

Most of the ringing was done in 2006 (74) and 2009 (41).

Sooty Tern monitoring Historically sooty terns had always bred on Cousine Island, but after many years of over collecting of their eggs, the sooty terns

eventually abandoned Cousine altogether. They were recently first recorded breeding in 2003 and have continued to do so in low numbers. The grassy area they prefer to use for nesting is usually cut to ground level and this usually stimulates the birds to come down and inspect the site prior to laying. All chicks are ringed and on a single occasion in 2006 a ringed bird from a previous season successfully nested on Bird Island. In 2007 many of the nests were disturbed by Wedge-tailed Shearwaters that also decided they liked the freshly cut areas and proceeded to dig burrows throughout the sooty colony, resulting in a 90% failure rate with only the few sooty nests located on rocks being successful. It is hoped, with the continued maintenance of their breeding sites, the Sooty Terns will return in greater numbers to breed on Cousine.

Lesser Noddy monitoring In 2007 the success rate was 69.3%, and 2008 had a very low success rate of 8.67% due to the ‘La Nina’ weather phenomenon, which accounted for food shortages and excessive hot dry weather. This season the success rate is looking much better and although the breeding season is not finished yet, the success rate so far is at 66%.

season experienced during 2008 the birds did not seem to breed. In April 2009 the Roseate Terns were back again, in the same area and in August the first chick was seen being fed by the adults close to the shore. An additional pair was also seen in the same general area and it is assumed that there may be two pairs breeding on Cousine. Unfortunately after much searching in the general area no nest could be found, but one would have to be very lucky to find a single nest on a rugged 26ha island. It may also be that the eggs had hatched and the cryptically colored chick was simply not seen. It is great to finally host a new species of breeding seabird, but one wonders how long they had been here in low numbers and had simply been overlooked.

Seabird Census All the breeding seabirds except for the two shearwater species are counted on Cousine Island during the annual seabird census, which is usually conducted in July during the peak breeding season of the Sooty Terns, and the Lesser and Brown Noddies. The island is divided into 96 sample plots, of which half are counted in a random fashion, so as to show no bias.

Each plot is 300 square meters and all birds are counted within this area. In the case of the White-tailed Tropicbirds and the Lesser and Brown Noddies, every nest is counted, which equals one pair per nest. In the case of the Fairy Terns, all nests that were seen were counted in addition to any pairs seen perching within each plot. Unfortunately both the White-tailed Tropicbirds and the Fairy Terns breed throughout the year and the weekly monitoring of the Tropicbird nests has shown that a third of all nests are occupied at any one time throughout the year, this means that the overall number of Tropicbirds and Fairy Terns counted during the annual seabird census is not representative of the actual population size which should be approximately three times the number counted during the census.

Other resident seabirds The numbers of Wedge-tailed Shearwaters continue to be very high with almost all burrows occupied and with no poaching activity recorded since 2006 the population appears stable. They do appear to breed all year with an obvious peak during the summer months. Audubon’s Shearwaters are still at relatively low numbers, but due to the difficulty in monitoring, it is assumed that the population stands at about 200 pairs. This species’ population was largely reduced due to the introduction of cats, but has been slow to recover since the eradication of cats in the 1970s. Any Audubon’s Shearwaters that are caught are ringed and so far only six adults have been ringed. The fairy tern population is doing very well, with large numbers seen breeding throughout the island. These birds also breed throughout the year and often go uncounted during the annual seabird census, due to the cryptic nature of their eggs and chick and their Year Lesser Noddy Brown Noddy WT TropicFairy Tern lack of obvious nests. It is suspected that bird during the censuses the population of 2006* 78916 5991 2445 1170 this species is vastly under estimated. The 2007 85886 1885 823 758 Brown Noddy population is also doing well, with the numbers of large planted 2008 23 689 3 575 867 975 coconut palms along the dune crest 2009 54690 2889 957 1174 increasing, resulting in more nest sites for Table 1. Results of the annual seabird censuses in Cousine from 2006-2009. these birds. They continue to nest in large *A different method was used by conservation staff in 2006, resulting in inconsistent numbers numbers in the rocky areas on the back of the island. The Bridled Tern population is also doing well, despite the difficulties in accurately counting The following graphs show the overall seabird population the numbers breeding on the island. An intensive count numbers on Cousine Island obtained during the annual conducted during the annual seabird census in 2008 revealed a seabird census from 1997 up to 2008. The unusual high total number of 451 pairs! numbers for 2006 represents the incorrect census technique used by conservation staff in that year. The low numbers New arrivals: Roseate Terns recorded during 2008 are due to the almost entire collapse of Since April 2007 a pair of Roseate Terns was regularly seen the breeding season due to the global weather phenomenon La flying around the North Point at dawn and dusk and later in Nina. the season they were seen and heard throughout the day. It was then suspected that there was possibly a small breeding population of one or two pairs some where in the North of the island. Sightings continued throughout that season and resumed again in April 2008, however due to the overall poor Seabird News Issue 5, November 2009

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Lesser Noddy Population Estimates

Brown Noddy Population Estimates Population Estimate Maximum Population Minimum Population

100000 80000 60000 40000

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Seabird census news from Cousin Island

By Gilles-David Derand

White-tailed tropicbird population appears relatively stable on Cousin, with 1,157 breeding pairs estimated in July 2009 compared to 1,255 pairs in July/August 2006 and 1,054 pairs in June/July 1999, using slightly differing sampling methods.

Brown Noddies on Cousin Island

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ince the last seabirds newsletter in June 2006, Cousin staff conducted annual census in July/August for white-tailed tropicbird, white tern, lesser and brown noddy. From February 2008, census for white-tailed tropicbird and white tern was also conducted during the North-West monsoon (February) in order to get a better understanding of seasonal variations in the population of these year-round breeding species.

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Seabird News Issue 5, November 2009

Conversely, the white tern breeding population appears to have decreased over the same 10 years period, from 3,606 pairs estimated in February 2000 to 2,006 pairs in February 2004 and 1,273 pairs in February 2009. However, for both white-tailed tropicbird and white tern, bi-annual censuses underestimate the actual breeding population as these species breed yearround on Cousin and only a part of the actual population can be intercepted.

The last census in July 2009 gave an estimate of 694 pairs of white tern, higher than July/August 2006 (379 pairs) and July 2007 (399 pairs), and similar to 675 pairs found in June 2005.

A census trial for Audubon’s shearwater run in July/August 2006 found 767 breeding pairs whereas 1,630 pairs were estimated in February 2004 and 5,177 pairs in February 2000 using slightly differing sampling methods.

The last census in July 2009 estimated only 401 breeding pairs on Cousin, and although this census may certainly have underestimate the actual population for various reasons and the fact that only a part of the actual population can be intercepted at any one time as this species also breeds year-round on Cousin, Audubon’s shearwater population also seems to have decreased on Cousin over the last 10 years.

The estimate of 66,272 pairs of lesser noddy in July 2009 is lower than the population estimates recorded between 2005-2007 (89,679 breeding pairs in June 2005 and 82,562 breeding pairs in July 2007), probably due to natural inter-annual variations in breeding population and very low breeding success recorded in 2008 in relation

with La Nina weather event. However, it is still comparable to the population estimates recorded between 1999-2002 (53,100 breeding pairs in June 2002 and 65,932 breeding pairs in June/July 1999) using slightly differing sampling methods.

For the brown noddy, the two annual censuses conducted in July/August 2006 and July 2007 indicated a relatively stable breeding population on Cousin with respectively 1,955 pairs and 1,861 pairs compared to 1,317 pairs estimated in 1999, although using slightly differing sampling methods.

Unfortunately, the last two estimates from June/July 2008 and July 2009 were evidently underestimated, notably due to inadequate census timing.

Bridled terns have a synchronized but non-annual breeding season in Seychelles and breeding occurs in cycles of 7-9 months, hence the census of this specie requires regular checks of breeding sites to determine the onset of laying so that the census can cover the

peak of laying and incubation. Due to inadequate timing, last census attempt in February 2009 gave a population estimate of only 86 pairs (including broken eggs, but excluding additional counts in between plots and along beach crest), whereas February 2007 census estimated 444 pairs on Cousin, a result still comparable to January/ February 2003 (577 pairs) and October 1999 (608 pairs estimated using a slightly differing sampling method).

Further bi-annual censuses at the same period of the year, repeating exactly the same methodology used for the different seabird species on Cousin, are needed in order to statistically confirm the trends inferred above.

Note: all the seabirds population estimates cited in this article are from unpublished report to Nature Seychelles between 1999 and 2009.

Please contact Nature Seychelles Science Coordinator for full references.

Year

WT Tropicbird

White Tern

Audubon’s shearwater

Lesser Noddy

Brown Noddy

Jul/Aug 2006

1,255 (1,031-1,479)

379 (217-541)

767 (553-981)

85,509 (74,201-96,817)

1,955 (1,082-2,828)

Feb 2007

Bridled Tern

444 (428-461)

Jul 2007

579 (384-768)

399 (233-565)

Feb 2008

522 (338-707)

1,715 (1,229-2,201)

Jun/Jul 2008

Feb 2009

964 (514-1,414)

1,273 (598-1,948)

Jul 2009

1,157 (812-1,502)

694 (421-967)

82,562 (66,741-98,383)

1,861 (1,005-2,717)

10,029* (7,374-12,683)

347* (46-657) 86* (16-156)

401 (133-670)

66,272 (54,398-78,145)

93* (21-165)

Table 1. Results of seabird censuses (Mean population estimates and 95% Confidence Interval) in Cousin from 2006-2009. * Underestimated notably due to inadequate census timing

Seabird News Issue 5, November 2009

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Articles:

Substitute Nest Provision for Fairy Terns (Gygis alba) on Cousine Island

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airy Terns are a common feature on Cousine Island which has a very healthy population. Unfortunately due to their unusual habit of not building a nest and laying their eggs in exposed positions on depressions on branched and rocks, many of the eggs succumb to harsh weather conditions especially strong winds. It is for this reason that a decision was made to provide the Fairy Terns with a safer alternative.

Since 1992 safe substitute nesting sites were provided for the resident Fairy Terns. Initially elaborate wooden structures were provided constructed from drift wood or pieces of plank.

Although these nesting sites were more natural looking, they required a fair amount of time to construct and set in place. The decision was then made try a much more readily available resource, in the form of coconut husks. The husks are removed from the nut, which is used for cooking and the husk is then discarded, which provided a continuous supply of substitute nests for the Fairy Terns.

Fresh husk (left) and trimmed husk (right)

The husks are the perfect shape, being concave with a depression in the centre, where the nut used to be. Only the larger pieces of husk are used and they are trimmed and the depression is neatened off and made deeper if required. The prepared husks are then taken to suitable ‘nest’ sites, usually situated on a horizontal or sloping branch, between 1.5 and 3 meters off the ground and nailed firmly in place.

A Fairy Tern quite happy with the new nest

The fairy terns seem to adopt the new ‘nests’ fairly quickly and up to 50% of all nests can be occupied within a few months. The new nests are safer for the eggs as they can’t fall out due to the depression created by the husk.

It is great seeing all the Fairy Terns on their nests in the forest and knowing that we are doing a great service to ensure they have safe nesting sites for the future.

Extending Seychelles Important Bird Areas (IBAs) to the marine realm

by Gilles-David Derand

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uring the sixth WIOMSA conference in La Reunion (2227th of August 2009), I gave an oral presentation, together with Ross Wanless from Birdlife South Africa Seabird Division and Nirmal Shah/ Nature Seychelles CEO, on how we could extent the existing Seychelles Important Bird Areas (IBAs) to the marine environment where seabirds on their feeding grounds are potentially subject to increasing pressures from fish overexploitation and by-catch.

BirdLife International’s Important Bird Areas programme has been instrumental in expanding protected areas and conserving critical bird habitats. Despite

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the obvious importance of the marine environment for seabird conservation, criteria for defining marine IBAs have only been addressed recently through the BirdLife International ‘Global Seabird Programme’. On the basis of seabirds triggering either global or regional criteria for IBAs designation, notably A1 criteria ‘Species of global conservation concern’ and A4 criteria ‘Congregations’, approximately 2,100 candidate marine IBAs have been identifies in 158 countries. Based on four broad categorizations of seabird distribution patterns, criteria for designating marine IBAs include seaward extensions of breeding colonies, non-breeding (coastal) concentrations, migratory bottlenecks

Seabird News Issue 5, November 2009

and areas for pelagic species (Howgate and Lascelles, 2007).

The 20 IBAs identified in the Seychelles

by Rocamora and Skerret (1999) cover only 656 km2 of (mostly lagoon) marine habitats, representing <0.1% of the Seychelles’ 1,374,000 km2 territorial waters, and only 6 sites are fully protected by law. Extending IBAs into the marine realm poses both conceptual and practical challenges and only seaward extensions of breeding colonies and areas for pelagic species may be applicable to the Seychelles’ context.

Phase one of this project aims to establish a definitive list of marine

Seabirds as bio-indicators in the Western Indian Ocean

IBAs in the Seychelles using the seaward extension of breeding colonies, which are used for feeding, maintenance behaviors and social interactions, and are limited by the foraging range of the species concerned and the oceanographic features (e.g. water depth). Ideally to define IBA boundaries for ‘trigger’ seabird species, remote-tracking of adequate sample of individuals of each IBA trigger species at a site should be carried out over several years. However this is not likely to be feasible for more than few sites, and thus we plan to use empirical data on foraging ranges of species studied at one site to model and map foraging ranges at other sites, notably using information available within the Birdlife Seabird Foraging Range Database.

Phase two aims to collaborate with other projects and researchers in using seabird tracking data (notably geolocators) and at-sea transects for defining pelagic IBAs. This will help define priority conservation areas for species with extensive feeding ranges.

As a complimentary strategy, we wish to conduct an ‘expert consultation’ process to determine pelagic areas of importance at a broad scale.

The expected outcomes of the project are notably the delivery of GIS maps and designation of seaward extensions to Seychelles terrestrial IBAs with seabird colonies, and the integration of Seychelles IBAs within local/ regional network of Marine Protected Areas (MPAs).

Literature cited: Howgate, E. and Lascelles, B. (2007).

Candidate Marine Important Bird Areas (IBAs). Global Status and Progress. Report to BirdLife International, Cambridge. March 2007 Rocamora, G. and Skerret, A. (1999).

First inventory of Important Bird Areas of the Republic of Seychelles.

Final version 25/08/99 with comments from IBA workshop of 07/08/98 integrated.

By Kévin Coustaut

Wedge-tailed shearwater © Michelle Kappes

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n the western Indian Ocean the two main changes which occurred during the last 30 years are global warming and the increase of industrial tuna fishery activities. The laboratory ECOMAR at the University of La Réunion, in collaboration with Nature Seychelles, initiated a long term monitoring research program, as part of a MASMA project funded by the WIOMSA (Western Indian Ocean Marine Science Association), to study the effects of these changes on seabird breeding parameters.

Ultimately, the goal is to use seabirds as bio-indicators of the health of marine ecosystems in the tropical western Indian Ocean. Seabirds are very abundant in the region (7 million pairs) and Seychelles hold almost half of the seabird biomass of the whole western Indian Ocean. Seabirds are very easy to study compared to others marine top predators, because they must come to land to breed, but they are totally dependent on the sea for food. In the tropics, they are mainly associated with tuna for finding their food, so we can expect that a decrease in tuna abundance, due to overfishing, will affect the prey accessible for seabirds.

The length of foraging trips, chick growth, body condition at fledging and breeding success were monitored since 2005 on Cousin Island, in austral winter and austral summer, on six seabird species: White tailed tropicbird, Fairy tern, Wedge-tailed and Audubon’s shearwaters, Brown and Lesser noddies.

Results suggest that environmental perturbations, such as ENSO events (El Niño Southern Oscillation) and positive IOD (Indian Ocean Dipole), affect almost all breeding parameters for the study species in austral winter 2006 and 2008.

The correlation between the breeding parameters and tuna catch was unclear, as tuna abundance is also affected by the marine environment. Responses to environmental changes were different for each seabird species. Seabirds with smaller foraging ranges, like noddies, were more affected by perturbations compared to less range-restricted species, like tropicbirds and shearwaters.

These observations highlight the importance of multi-species monitoring programs to understand the ecological consequences of environmental variability.

Over the long term, this monitoring will be useful to better understand the impact of natural and man-induced perturbations on the functioning of the marine ecosystems in the western tropical Indian Ocean.

Kévin Coustaut is a MSc student working under the supervision of Pr. Matthieu Le Corre and Dr. Sébastien Jaquemet in the laboratory ECOMAR at the University of La Réunion.

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The secret lives of shearwaters

By Michelle Kappes and Kevin Coustaut

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hearwaters, like most seabirds, spend most of their lives at sea. In order to learn about where shearwaters go when they are away from their breeding colonies, Dr. Matthieu Le Corre from the Université de la Réunion has begun a research program to deploy miniaturized electronic tags on wedgetailed shearwaters (Puffinus pacificus) at sites throughout the western Indian Ocean. These tags, or geolocators, collect data on light level that can be used to determine the position of the bird at sea. Basically, the time of local noon is used to determine longitude, and latitude is estimated by local day length.

The tags are attached to a metal ring on the bird’s tarsus using a plastic zip-tie (see photo). The tags also have a saltwater switch, and due to their placement, we can determine when the shearwaters are in flight and when they are resting or foraging on the sea surface. By taking advantage of this technology, we can begin to get a picture of how these wideranging seabirds behave during their foraging trips to sea.

Also using geolocators, recent work by Catry et al. (2009) demonstrated that 9 wedge-tailed shearwaters breeding on Aride Island remained close to the colony when raising chicks, and later dispersed up to 3,500 km to the central Indian Ocean Basin during the non-breeding period. Last year, members of Dr. Le Corre’s research team recovered 6 geolocators from wedge-tailed shearwaters deployed at Cousin Island. Preliminary analysis

suggests that shearwaters from Cousin Island disperse further east during the nonbreeding period than those from Aride Island. However, a larger sample size will be necessary to confirm colonyspecific differences in foraging behavior.

During 14-29 September 2009, we deployed 24 geolocators on wedge-tailed shearwaters breeding within St Joseph Atoll, Amirantes group, and 24 geolocators on shearwaters breeding at Cousin Island.

Field work is planned to deploy similar numbers of geolocators at sites on Réunion Island, as well as off Mauritius and Madagascar. This will be the first attempt to simultaneously study the at-sea behavior of this seabird species across a broad range of breeding sites.

Ultimately, these data will help us answer questions such as: do wedgetailed shearwaters breeding at different sites in the western Indian Ocean travel to similar locations at sea? Are there specific ocean habitats that are of particular importance for this species?

Areas of the ocean that are important to shearwaters may be important for other marine species as well, so these data could be used to help identify marine Important Bird Areas and possibly oceanic Marine Protected Areas.

However, as the geolocators store these data on-board, we won’t be able to answer these questions until we recover the tags at the end of the breeding season. This may prove trickier than it sounds because once shearwater chicks reach about a week in age, adults only return to the colonies for brief periods to deliver meals to their chicks. So we may have to wait until the next breeding season starts in 2010 to recover these tags and unlock the secrets of where these different populations of shearwaters spend their time at sea!

Literature Cited: Catry, T., J. A. Ramos, M. Le Corre, and R. A. Phillips. 2009. Movements, at-sea distribution and behaviour of a tropical pelagic seabird: the wedge-tailed shearwater in the western Indian Ocean. Marine Ecology Progress Series 391: 231–242.

Effects of Pisonia grandis on seabirds

by David Andrews and Gilles-David Derand

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pecies of tree within the genus Pisonia are found on seabird islands throughout the tropical oceans and are able to flourish in the highly acidic guano soil and use the seabirds to disperse their seeds. However, the relationship between Pisonia and its seabird disperser is complex and often fatal for the birds (Burger, 2005); the seeds of the Pisonia become entangled in the feathers often preventing the bird from flying and feeding, resulting in death.

Thus, the aim of the survey conducted

by Nature Seychelles with the help of 8

David Andrews from the University of East Anglia/UK, was to establish a standardised procedure in order to quantify the effect and scale of Pisonia induced mortality on seabirds, to investigate the phenology* of Pisonia and gain an insight into the evolutionary process which has formed this unique relationship, and to provide a factual basis for the possibility of vegetation management. Cousin Island was the main survey site but Aride Island was also visited twice between April and June 2009. Effects of Pisonia on seabirds were quantified by systematic search of any bird unable to fly or dead

Seabird News Issue 5, November 2009

due to Pisonia gluing in a randomly selected sample of 20 grid squares on Cousin for 15 minutes each, and the seeding phenology of Pisonia was studied comparing two different methods: recording seeding intensity by determining the proportion of each trees canopy that was bearing seeds, and recording the amount of seeds on the ground by dragging an imitation bird over a distance of 50m through the selected grid-square.

Over the three months of fieldwork, a total of 484 seabirds of five species were found dead or dying on Cousin and

of year and is not directly related to weather variables.

This study and the severe impact that Pisonia may have upon seabirds raises the question of whether current densities of Pisonia on Cousin and across the Seychelles are above natural levels. One possible interpretation is that, although Pisonia grandis is native to the archipelago, its fast postrestoration establishment, both from seeds and vegetative regeneration of fallen trees or branches, has led to a high density, which has been suggested is higher than ever before, possibly because slower growing climax vegetation is yet to mature.

White Tern with pisonia seeds

the estimated number of birds killed during this period is 2,444. Five out of seven species of seabirds were victims of Pisonia on Cousin, Wedge-tailed Shearwater and Bridled tern were not found to be affected during routine surveys. However the two species were both found affected on Aride. Lesser Noddies were the most common victim of Pisonia, however as a population, the White Tern was the most affected on Cousin. As little as four seeds sticking the wingtips together were able to disable an adult bird, this ultimately leading to death in a relatively short time due to starvation.

The survey also showed that White-tailed Tropicbirds and Audubonâ&#x20AC;&#x2122;s Shearwaters were significantly impacted on Cousin, in accordance with Catry et al. (2009) who recognised a decline in White-tailed Tropicbird on Aride with Pisonia induced mortality being identified the main cause.

The limitation of this study to three months does not allow conclusive figures of Pisonia impact and a more long-term study is needed to understand the full situation. There are important conservation implications arising from this study involving the management of vegetation and the possible control of Pisonia. A reduced Pisonia dominance could be achieved by increasing diversity and encouraging the succession of the island woodland, notably through the manual spreading of native species seeds (e.g.

Takamaka Calophyllum inophyllum, Badamier Ternzinalia catappa, etc), the prevention of vegetative Pisonia re-growth (when a tree/branch falls, remove new shoots) in the vicinity of young trees of other species such as Ochrosia oppositifolia and Morinda citrifolia, and possibly the cut-down of a number of large Pisonia trees. *: Phenology is the study of periodic plant and animal life cycle events and how these are influenced by seasonal and interannual variations in climate

Figure: Estimated total Pisonia induced mortality over the period of the study on a week by week basis on Cousin Island. The chart also displays the number of each species of seabird affected per week. This constitutes a minor seeding event with a maximum of 12.5% of Pisonia trees in seed at any one time.

Regarding the phenology of Pisonia, a minor seeding event occurred on Cousin with a maximum of 12.5% of Pisonia trees in seed at any one time, but a major seeding event also occurred on Aride which saw approximately 60-80% of the Pisonia trees producing ripe seeds. All references to Pisonia suggest that seeding events can occur at any time of year and that seeding is relatively random. This lack of seeding seasonality means that seabirds have been unable to evolve to avoid Pisonia by breeding at a certain time. In fact, Pisonia has a very non-dense trunk and therefore can store a lot of water, and this can partly explain why Pisonia can seed at any time

Literature cited: Burger, A. E. (2005) Dispersal and germination of seeds of Pisonia grandis, an Indo-Pacific tropical tree associated with insular seabird colonies. Journal of Tropical Ecology, 21:263â&#x20AC;&#x201C;271 Catry, T., Ramos, J.A., Monticelli, D., Bowler, J., Jupiter, T., LeCorre, M. (2009). Demography and conservation of the White-tailed Tropicbird Phaethon lepturus on Aride Island, Western Indian Ocean. Journal of Ornithology 150: 661-669

Seabird News Issue 5, November 2009

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Caspian Terns on Aldabra Atoll Naomi Doak

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ldabra is well known for its unique bird life and large colonies of nesting seabirds, most notably the greater and lesser frigatebirds and the red-footed boobies, which nest in large numbers on the atoll. Many of the species of seabird that utilise the atoll for breeding and nesting are less well known to visitors. This includes a particularly special species, the Caspian tern Hydroprogne caspia. Aldabra is the only location in the Seychelles where this species breeds and it is the only non-continental breeding area for the species in the world; the species primarily breeds close to lakes and on continental ocean coastlines.

The Caspian tern is the largest species of tern and is easily identified by its large size (48-56 cm in length), powerful build (574–782g), broad wings (wingspan: 127–140 cm) and, most obviously, its large bright red or orange-red bill. During the breeding season the adults develop a striking black cap, with juveniles identified by their dark tipped bill, mottled underparts and a reduced amount of black on the head with the cap usually appearing grizzled black and white.

While the Caspian tern is a common resident in coastal areas of nearby Madagascar, it is considered a vagrant to the central Seychelles islands as well as the Comoros which makes the breeding population on Aldabra of particular importance. The species nests on sand or coral shingle and usually just above high tide mark on the foremost sand dune. Far less gregarious than other terns, Caspians usually feed singly and, on Aldabra, most birds appear to breed in isolated pairs on a number of the beaches around the atoll or in small colonies on a couple of the islets inside the lagoon. In the past, breeding of this species on Aldabra has been irregularly recorded in locations found throughout the lagoon and atoll, including Iles Moustiques, Ile Espirit, La Gigi, Anse Grand Poche, Champignon des Os and Ile Sylvestre.

Caspian tern chicks © Naomi Doak

Other species of tern regularly spotted on Aldabra include the greater crested tern, lesser crested tern, white (fairy) tern, black-naped tern and sooty tern.

While Caspian terns are not considered internationally to be an endangered species, the Aldabra colony is both interesting and significant as this is currently Seychelles’ rarest breeding bird and Aldabra is the world’s only oceanic population.

Some observations were made on the breeding activity of this species in the 1980s with inundation of nests being the major cause of egg loss. Despite these early observations of breeding there is still little known about this species on Aldabra.

Consequently, observations are continuing, with increased effort being planned for future breeding seasons.

Observations made over the most recent breeding season have provided additional information on breeding locations as well as some early data on breeding success. Although Caspian tern chicks can vary in their colour morph, preliminary observations indicate that the chicks hatching on the atoll may well be predominantly dark morph chicks.

Unfortunately the nesting pair found and monitored on Picard were unsuccessful in both of their breeding attempts, with two sets of eggs both predated at the egg stage. Potential predators include rats, rails, crows, herons and egrets. Breeding pairs in other locations around the atoll were more successful in their breeding with several chicks fledging.

Caspian tern breeding on Aldabra occurs from June to August with eggs hatching after 26-28 days and chicks fledging after 35-45 days, although they are able to leave the nest after only a few days. The chicks are variable in plumage pattern, from pale cream to darker grey-brown.

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Seabird News Issue 5, November 2009

We have a long way to go in finding out more about this important Aldabran population of seabirds but we have made a promising start with the compilation of previous observations and data, initiated collection of new data and laid the groundwork for future work on this species in the Seychelles.

It is a positive sign that we have observed chicks fledging this breeding season, despite high numbers of potential predators of these vulnerable ground nesting birds. The next stage will be to identify the predators and collect more data to quantify the threats, assess the population and decide whether management interventions are necessary to protect this impressive species.