Rachel Bristol (Project Officer under the Seychelles Paradise Flycatcher project) visited Denis last week to catch up on the Flycatcher population there and their status. On her return she was able to report some excellent progress including the commencement of breeding activities for the new season and some early successes, Rachel Continues below:
“After a few months break the flycatchers on Denis have started breeding in force again. Flycatchers can breed year–round but there is a marked peak in breeding during the North-West or rainy season from November- April. However, the dry South-East season this year has been considerably wetter than usual which likely explains the early start to the breeding season.
I was on Denis last week and of 8 potentially breeding pairs six of them are currently active. We have 2 new fledglings that fledged two weeks ago and yesterday (19 October 09) respectively, a nestling just hatched yesterday and 2 further pairs are nest building. A 6th pair has a dependant juvenile that fledged in August.
Now almost 11 months since the Conservation Introduction of 23 flycatchers to Denis we are beginning to get an idea of how successful the introduction will be. The current population is 24 individuals; we have lost 4 of the original introduced stock but have had 5 chicks fledge on Denis. After a shaky start where the majority of nesting attempts were failing (due to a combination of eggs failing to hatch and de-predation of both eggs and nestlings- [ed: most likely by Mynah Birds a problem which still requires redress]) the flycatchers appear to be “getting it together” and successfully breeding on Denis- the key to establishment of a self-sustaining population.”
This really is fantastic news – the Flycatcher transfer to Denis in November of last year was the first ever transfer of this critically endangered species and constitutes a key step in securing the future of this beautiful and iconic endemic species.
This success is largely down to the tireless efforts of Rachel over the previous three years. Rachel is currently working to complete her PhD thesis on the species and we wish her all the best in her ongoing endeavours.
While she was on Denis Rachel took the opportunity to measure and ring a flycatcher nestling and has kindly sent us some great photos of the young bird see photos in sidebar.
The Seychelles Paradise Flycatcher Project is a multi-partner undertaking funded by the Darwin Initiative and supported by partners including Nature Seychelles, the University of Kent, the La Digue Development Board, Denis Island and the DoE.
Wednesday, October 21, 2009
Friday, October 2, 2009
All creatures great and small…
It has indeed been a considerable time since I last visited Denis as a confluence of events and paperwork deadlines have kept me “trapped” on the main island of Mahe. This has in turn meant a marked decrease in my posts from an average of 8 posts a month through July to just 2 and 1 in August and September respectively.
This, by chance, has meant that visitors to the blog of late have been greeted upfront by photos of the Seychelles skink and a couple of species of crab – perhaps not everyone’s cup of tea or idealised perception of an idyllic tropical island. At this point it is timely for me to state that Denis is very much the epitome of a picture postcard tropical island and I am certain will meet the requirements of such from its visitors.
The spectre of brown lizards and hairy-legged crabs has however been visited upon me today by a member of the island’s marketing section concerned that the perception generated is inappropriate. Perception is of course - in these modern times of multi-media, sound bites, 24-hour news and spin-laden politics - increasingly everything with substance coming often at best second.
Lizards and crabs play a vital role in the island’s ecosystem breaking down detritus and recycling nutrients. It is imperative in the management of fragile islands that a comprehensive ecosystem approach to environment is utilised and that all native species, regardless of aesthetic appeal, are incorporated therein. Without one there is often not the other as each contributes to the health of the whole.
However, visitors to this blog and prospective visitors to Denis Island can rest assured that they will find yearnings for both perception and substance satisfied in the environmental management of the island. That is not to say all is perfect, the rehabilitation and restoration of the island’s ecosystem is a long term process but great steps have been made.
The key alien predators, cats and rats, were removed in 2000 and 2002 respectively. This coupled with extensive habitat rehabilitation paved the way for the introduction of rare and threatened species such as the Seychelles warbler, Seychelles fody, the endangered Seychelles magpie-robin and the first ever transfer of the critically endangered Seychelles paradise flycatcher.
Thankfully from a marketing perspective these birds are also pretty… see photos in sidebar.
Meanwhile the work continues on all creatures great and small.
This, by chance, has meant that visitors to the blog of late have been greeted upfront by photos of the Seychelles skink and a couple of species of crab – perhaps not everyone’s cup of tea or idealised perception of an idyllic tropical island. At this point it is timely for me to state that Denis is very much the epitome of a picture postcard tropical island and I am certain will meet the requirements of such from its visitors.
The spectre of brown lizards and hairy-legged crabs has however been visited upon me today by a member of the island’s marketing section concerned that the perception generated is inappropriate. Perception is of course - in these modern times of multi-media, sound bites, 24-hour news and spin-laden politics - increasingly everything with substance coming often at best second.
Lizards and crabs play a vital role in the island’s ecosystem breaking down detritus and recycling nutrients. It is imperative in the management of fragile islands that a comprehensive ecosystem approach to environment is utilised and that all native species, regardless of aesthetic appeal, are incorporated therein. Without one there is often not the other as each contributes to the health of the whole.
However, visitors to this blog and prospective visitors to Denis Island can rest assured that they will find yearnings for both perception and substance satisfied in the environmental management of the island. That is not to say all is perfect, the rehabilitation and restoration of the island’s ecosystem is a long term process but great steps have been made.
The key alien predators, cats and rats, were removed in 2000 and 2002 respectively. This coupled with extensive habitat rehabilitation paved the way for the introduction of rare and threatened species such as the Seychelles warbler, Seychelles fody, the endangered Seychelles magpie-robin and the first ever transfer of the critically endangered Seychelles paradise flycatcher.
Thankfully from a marketing perspective these birds are also pretty… see photos in sidebar.
Meanwhile the work continues on all creatures great and small.
Wednesday, September 2, 2009
The Seychelles Skink (Mabuya sechellensis)
A common sight on the ground in the woodlands of Denis, and indeed throughout the central Seychelles archipelago is the Seychelles skink (Mabuya sechellensis). This species is endemic to the central Seychelles.
On Denis this coppery-brown lizard gets up to approximately 22-23cm in length – including its tail. It has a distinct pale stripe running from above the eye down the top of each flank fading out at the tail. This stripe is emphasised by rows of darker patches running above and below it (see photos). This pale stripe and the pale belly in turn make the flanks appear as a brown stripe. The striping varies in prominence from island to island with adults in some populations reportedly not having stripes.
On some islands the skink can reach very high densities (e.g. Cousin) but this is not the case here. On Denis one generally first notices a skink by a rustle in the undergrowth as it seeks to avoid our great marauding feet! The best way to observe them I have found is by moving off the paths into areas of broadleaved woodland and just finding a comfortable perch. Once still, one rapidly becomes aware of the movement of the skinks across the forest floor and they often approach as curiosity brings them in search of food.
Gerlach (2007) states that the skink has been introduced to Denis and some credence is provided to this idea by the fact that no skinks were recorded on Denis’ nearest neighbour Bird in 1908 (Fryer 1910) but were subsequently found in 1939 – a timeframe highly suggestive of a human vector. For Denis though it is not so conclusive. Skinks were recorded in 1908 and it is definitely possible that they could have arrived on Denis during its 14,000 year history through natural means – i.e. “rafting” on floating vegetation.
Regardless the skink, as a species endemic to the central archipelago, is treated as native species and serves an important role in the ecosystem feeding omnivorously on insects, fruit, detritus and carrion. Skinks also provide a source of food for moorhens and interestingly the endangered magpie-robin which is highly adept at swooping down on an unsuspecting young lizard and despatching it clinically by 2 or 3 hard “thwacks” against a stone before consuming it.
The skinks lay 2 or more oblong, leathery white eggs and cover them with soil. We do anticipate that as sea bird colonies increase on the island that the detritus they bring – small fish, droppings, eggs and dead birds – will see a corresponding increase in the skink population.
Refs:
Fryer, J.C.F. (1910). Bird and Denis Islands, Seychelles. Trans. Linn. Soc. Land. (2)14: 15-20.
Gerlach, J. (2007). Terrestrial and Freshwater Vertebrates of the Seychelles Islands. Backhuys Publishers. The Netherlands.
On Denis this coppery-brown lizard gets up to approximately 22-23cm in length – including its tail. It has a distinct pale stripe running from above the eye down the top of each flank fading out at the tail. This stripe is emphasised by rows of darker patches running above and below it (see photos). This pale stripe and the pale belly in turn make the flanks appear as a brown stripe. The striping varies in prominence from island to island with adults in some populations reportedly not having stripes.
On some islands the skink can reach very high densities (e.g. Cousin) but this is not the case here. On Denis one generally first notices a skink by a rustle in the undergrowth as it seeks to avoid our great marauding feet! The best way to observe them I have found is by moving off the paths into areas of broadleaved woodland and just finding a comfortable perch. Once still, one rapidly becomes aware of the movement of the skinks across the forest floor and they often approach as curiosity brings them in search of food.
Gerlach (2007) states that the skink has been introduced to Denis and some credence is provided to this idea by the fact that no skinks were recorded on Denis’ nearest neighbour Bird in 1908 (Fryer 1910) but were subsequently found in 1939 – a timeframe highly suggestive of a human vector. For Denis though it is not so conclusive. Skinks were recorded in 1908 and it is definitely possible that they could have arrived on Denis during its 14,000 year history through natural means – i.e. “rafting” on floating vegetation.
Regardless the skink, as a species endemic to the central archipelago, is treated as native species and serves an important role in the ecosystem feeding omnivorously on insects, fruit, detritus and carrion. Skinks also provide a source of food for moorhens and interestingly the endangered magpie-robin which is highly adept at swooping down on an unsuspecting young lizard and despatching it clinically by 2 or 3 hard “thwacks” against a stone before consuming it.
The skinks lay 2 or more oblong, leathery white eggs and cover them with soil. We do anticipate that as sea bird colonies increase on the island that the detritus they bring – small fish, droppings, eggs and dead birds – will see a corresponding increase in the skink population.
Refs:
Fryer, J.C.F. (1910). Bird and Denis Islands, Seychelles. Trans. Linn. Soc. Land. (2)14: 15-20.
Gerlach, J. (2007). Terrestrial and Freshwater Vertebrates of the Seychelles Islands. Backhuys Publishers. The Netherlands.
Friday, August 28, 2009
Catching-up…
Leave and then the frantic writing of a project proposal to meet the donor deadline have kept me from posting for nearly a month and away from the island for longer, so just a few quick bullets to bring the blog up to date:
- Great news from Rachel, we have now our third successful fledging of a Seychelles paradise flycatcher on the island which is most encouraging. Breeding activity has now ceased as is usual for this time of year.
- Vicki and Georgia headed home at the end of July. Their work on the Sooty tern project was very fruitful with numerous landings recorded and very encouraging behaviour displayed. We believe that the birds that visited the island this year are young adults that have not previously bred reconnoitring potential breeding sites for the future. If so this is indeed a very encouraging development. I look forward to receiving the write-ups of their work and also hopefully they will contribute a post or two to the blog.
- Jildou and Peter have finished their work on the warblers (Acrocephalus sechellensis) on Denis for this visit and dropped by to the office last week to update me on their findings. They were able to catch and ring 99 birds during their stay and estimate that the island population is about 150 - 175 birds. There are now approximately 75 territories on the island. Once independent, young birds leave their natal territories. There are therefore a certain number of birds “floating”. That is to say moving round the island looking for a territory of their own. On Cousin Island where the warbler population is at carrying capacity the birds exhibit cooperative breeding where the young, and particularly the females, often remain in their natal territory and help their parents raise the next generation of siblings. This different life tactic is utilised because the entire existing habitat is occupied and the bird’s evolutionary fitness is optimised by helping to raise its siblings and seeking over time to either inherit the territory or gradually establish a territory off the side of the existing one. The high proportion of unringed birds found in the population during this visit is evidence of ample successful breeding but also suggests a quite high rate of adult mortality. Of particular concern is that Jildou and Peter estimate that 1 in 5 of the adults shows evidence of scarring and injury around the head. Such injuries are not evident on the other island populations and once again suspicion points to the predatory impact of the invasive Mynah bird.
I don’t know when I will be going back to the island, but I do have a backlog of a few things I could post on so I will try and post a couple of times over the next week. Keep checking back for updates…
Monday, August 3, 2009
More on littoral crabs... new records for Denis Island.
I posted at length on the 5th of July on the Sally lightfoot crab (Grapsus tenuicrustatus) and was able to get a few good shots of the animals as waves broke over them. G. tenuicrustatus is a common sight on the sandstone formations to be found around the southern and eastern coastline of the island and is indeed the only rocky shore crab previous studies have recorded on the island. I was very interested therefore to find other species present in the southern rocks when I was trying to get photos of G. tenuicrustatus. They were much more shy than the “Lightfoots” and difficult to photo but I was able to get a few snaps sufficient for their identification.
Eriphia smithi – rough red-eyed crab, red-eyed reef crab, pebble crab
E. smithi has an indo-pacific distribution and is reportedly very common on east African coasts. It has various distinctive characteristics which when combined allow for species identification. Most apparent are the bright red eyes on white stalks and this immediately narrows down its identity, this coupled with the numerous spines on carapace edge behind the eyes and the large molariform tooth on the larger claw clearly identify it as E. smithi.
This is an interesting species that grazes on algae during the day but turns predator of crustaceans and molluscs at night. At low tide at night individuals have been reported to roam out up to 50m on to reef flats in search of prey before returning to their crevice hideouts (Vaninni et al 1989). Rock crevices play an important part in their lifecycle for seclusion and mating and individual crabs can remain loyal to a single retreat for 3 weeks or more. The southern reaches of the island seem ideal in this regard with numerous cracks and crevices in the sandstone and large reef flats that are exposed at low tide.
Geograpsus stormi – red nipper.
Now I can’t be sure of this identification as I do not yet have a full dorsal photo of this crab (it moved very rapidly and agilely over the rocks in its search of refuge) but judging from the colour of its legs and eyes and the presence of prominent long bristles on the legs I am fairly certain that it is a specimen of the rocky shore crab G. stormi .
G. stormi has a western Indian ocean to central pacific distribution (Richmond 1997) and has been noted for its consumption of rocky shore carrion. Interestingly Haig (1984) records G. stormi as only occurring on islands that fit the habitat category of “low islands with mangroves” - in this case citing the outer island atolls of Aldabra and Cosmoledo. She does however go on to note that it is likely that G. stormi (inter alia) will be found on islands without mangroves as more “collecting” is done.
References:
1). Cook Islands biodiversity Database (2009). http://cookislands.bishopmuseum.org/species.asp?id=7351
2). Haig, J. (1984). Land and freshwater crabs of the Seychelles and neighbouring islands. In: Stoddardt, D.R. Biogeography and ecology of the Seychelles islands. Junk Publishers, The Hague.
3). Richmond, M.D. (1997). A guide to the seashores of Eastern Africa and the Western Indian Ocean Islands. ISBN 91-630-4594-X.
4).Vaninni, M. et al (1989). Feeding habits of the pebble crab Erithia smithi. Marine Biology 100, (249 -252) 1989.
Eriphia smithi – rough red-eyed crab, red-eyed reef crab, pebble crab
E. smithi has an indo-pacific distribution and is reportedly very common on east African coasts. It has various distinctive characteristics which when combined allow for species identification. Most apparent are the bright red eyes on white stalks and this immediately narrows down its identity, this coupled with the numerous spines on carapace edge behind the eyes and the large molariform tooth on the larger claw clearly identify it as E. smithi.
This is an interesting species that grazes on algae during the day but turns predator of crustaceans and molluscs at night. At low tide at night individuals have been reported to roam out up to 50m on to reef flats in search of prey before returning to their crevice hideouts (Vaninni et al 1989). Rock crevices play an important part in their lifecycle for seclusion and mating and individual crabs can remain loyal to a single retreat for 3 weeks or more. The southern reaches of the island seem ideal in this regard with numerous cracks and crevices in the sandstone and large reef flats that are exposed at low tide.
Geograpsus stormi – red nipper.
Now I can’t be sure of this identification as I do not yet have a full dorsal photo of this crab (it moved very rapidly and agilely over the rocks in its search of refuge) but judging from the colour of its legs and eyes and the presence of prominent long bristles on the legs I am fairly certain that it is a specimen of the rocky shore crab G. stormi .
G. stormi has a western Indian ocean to central pacific distribution (Richmond 1997) and has been noted for its consumption of rocky shore carrion. Interestingly Haig (1984) records G. stormi as only occurring on islands that fit the habitat category of “low islands with mangroves” - in this case citing the outer island atolls of Aldabra and Cosmoledo. She does however go on to note that it is likely that G. stormi (inter alia) will be found on islands without mangroves as more “collecting” is done.
References:
1). Cook Islands biodiversity Database (2009). http://cookislands.bishopmuseum.org/species.asp?id=7351
2). Haig, J. (1984). Land and freshwater crabs of the Seychelles and neighbouring islands. In: Stoddardt, D.R. Biogeography and ecology of the Seychelles islands. Junk Publishers, The Hague.
3). Richmond, M.D. (1997). A guide to the seashores of Eastern Africa and the Western Indian Ocean Islands. ISBN 91-630-4594-X.
4).Vaninni, M. et al (1989). Feeding habits of the pebble crab Erithia smithi. Marine Biology 100, (249 -252) 1989.
Friday, July 24, 2009
Nature Notes & Bird Bulletin…
I am taking some leave in the coming weeks so posts will likely be scarce for a good few weeks. I will use this combined “Nature Notes & Bird Bulletin” post to summarise a few odds and ends from my last island visit.
Nature Notes
Magpie Robin News. We have experienced some considerable set-backs in recent months with several chicks lost to Mynah bird attacks and two adults lost to illness. This is a matter of real concern as the population has decreased to 20 birds which is the number we started with a year ago and we have lost more females than males from the adult population. It is urgent that we take measures to improve breeding success in the population. The estate has been assisting with localised habitat management creating higher quality feeding grounds in each territory. Meanwhile I am in final negotiations with the island under what conditions we can bring a marksman to the island to undertake a preliminary cull of the Indian mynah population. The Indian mynah (Acridotheres tristis) is an invasive alien species in Seychelles and a highly effective predator of the eggs and chicks of our rare endemic species – so we have to deal with it. On a positive note I encountered a family group of three birds on the path called “L’Allee Bodamye” I was walking from the central path junction in the island when I noticed a single SMR following me. I took the opportunity disturb the leaf litter with my feet in order expose the insects upon which the bird feeds and moved on. When I looked back there were three birds on the patch of scraped ground. Such a sight even today is significant as it represents approximately a 60th of the world’s entire population of this endangered species. So I turned to take a few photos. One of the adults on seeing that I had stopped however soon came forward making its “churring” aggressive call. So not wanting to stress the birds I cleared another patch of leaves and left them to their foraging.
L’Allee Sed. The path that leads from the west coastal path to the island’s main central junction (mentioned above) is called “L’Allee Sed” because it is formed by an avenue of casuarina trees. L’Allee Sed is one of the older features on the islands. Casuarina trees were likely planted on the island from the 1860s onwards to provide a better windbreak for the coconut plantations and I have found reference from 1907 to the stands on the island being a major feature. The L’Allee Sed is therefore recognised under the island’s management plan as an important historical and ecotourism feature of the island that needs to be maintained.
Sally lightfoot crabs. In my post of 5th July I wrote about this species of crab and its special adaptations to life in the breaking waves. I also mentioned that on occasion the cast off exoskeletons could sometimes be found. During my last trip I indeed find one on the southern rocks see photo in sidebar.
Bird Bulletin
Nature Notes
Magpie Robin News. We have experienced some considerable set-backs in recent months with several chicks lost to Mynah bird attacks and two adults lost to illness. This is a matter of real concern as the population has decreased to 20 birds which is the number we started with a year ago and we have lost more females than males from the adult population. It is urgent that we take measures to improve breeding success in the population. The estate has been assisting with localised habitat management creating higher quality feeding grounds in each territory. Meanwhile I am in final negotiations with the island under what conditions we can bring a marksman to the island to undertake a preliminary cull of the Indian mynah population. The Indian mynah (Acridotheres tristis) is an invasive alien species in Seychelles and a highly effective predator of the eggs and chicks of our rare endemic species – so we have to deal with it. On a positive note I encountered a family group of three birds on the path called “L’Allee Bodamye” I was walking from the central path junction in the island when I noticed a single SMR following me. I took the opportunity disturb the leaf litter with my feet in order expose the insects upon which the bird feeds and moved on. When I looked back there were three birds on the patch of scraped ground. Such a sight even today is significant as it represents approximately a 60th of the world’s entire population of this endangered species. So I turned to take a few photos. One of the adults on seeing that I had stopped however soon came forward making its “churring” aggressive call. So not wanting to stress the birds I cleared another patch of leaves and left them to their foraging.
L’Allee Sed. The path that leads from the west coastal path to the island’s main central junction (mentioned above) is called “L’Allee Sed” because it is formed by an avenue of casuarina trees. L’Allee Sed is one of the older features on the islands. Casuarina trees were likely planted on the island from the 1860s onwards to provide a better windbreak for the coconut plantations and I have found reference from 1907 to the stands on the island being a major feature. The L’Allee Sed is therefore recognised under the island’s management plan as an important historical and ecotourism feature of the island that needs to be maintained.
Sally lightfoot crabs. In my post of 5th July I wrote about this species of crab and its special adaptations to life in the breaking waves. I also mentioned that on occasion the cast off exoskeletons could sometimes be found. During my last trip I indeed find one on the southern rocks see photo in sidebar.
Bird Bulletin
- I am pleased to report that both Paradise flycatcher fledglings are alive and well. Rachel Bristol, the Flycatcher Project Officer, is currently out on the island to follow up on the population so I should have more detailed news soon.
- Sadly the ground-nesting Tropicbird to the south of the island that fledged its first chick in December appears to have abandoned its nest without breeding this time – there are few factors that may be involved and I will follow up on the site closely.
- I noted only 1 Crested tern on the island last weekend interesting as I had recorded my highest ever count of 15 only a few weeks ago (see Post of 8th June).
- Sooty terns are a common sight and sound overflying the island aside from the actual project area they are particularly notable displaying over the northwest coast at Pte Mme Guichard.
- I checked on the White tern chick, the rescue of which I reported on in my second post of 5th July and am happy to report that it is growing well see photo in sidebar.
Wednesday, July 22, 2009
Studying the Seychelles warbler population on Denis…
As mentioned in my post of 8th June arrangements had been made for some researchers from Groningen University in the Netherlands to come to Denis to undertake a study of the Seychelles warbler (Acrocephalus sechellensis). The Seychelles warbler was introduced to Denis in 2004 as part of its ongoing national conservation plan (see post of 08/06 for more info).
The researchers Jildou and Peter arrived three weeks ago and were straight into their work. The establishment of a new population on an island offers plenty of scope for research. Jildou and Peter will be investigating the warbler’s population growth since 2007 and undertaking a detailed survey to ascertain survival and reproductive success in the population. Jildou and Peter are working under the supervision of Dr Jan Komdeur who worked in Seychelles for several years in the late 1980’s and early 1990’s. Jan was the man responsible for the propagation of the warbler to other islands that has done so much to enhance the conservation status of this endemic species. His detailed research of the warbler and its habitat requirements enabled the transfer of birds from the then sole colony on Cousin island to the islands of Aride and Cousine and latterly Denis.
Jildou and Peter are looking in particular at female mortality. There is evidence from the previous Denis survey in 2007 that the warbler population was skewed, with more males than females. Birds on a new island with abundant vacant habitat undergo more rapid reproduction than they do in established populations simply because resources are more abundant. Breeding is an energy intensive activity particularly for the females. It is postulated that this investment by the females may detract from their longevity and hence the development of a skewed sex ratio in the population.
Jildou and Peter will therefore be monitoring levels of stress in the birds by taking blood samples and checking for levels of oxidative stress, they will also be looking at the level of stress hormones in warbler faecal samples. They are furthermore looking at the levels of immunocompetence in the birds by assessing a variety of physical characteristics of the birds – as stress can affect immunocompetence.
This research is very interesting and has various ramifications for the planning of bird translocations in the future. From a Denis viewpoint, we are particularly interested in an update on the status of the population, its distribution and habitat use as this will help inform decision-making with regard to vegetation management on the island.
Keep checking back for more updates on Jildou and Peter’s endeavours.
The researchers Jildou and Peter arrived three weeks ago and were straight into their work. The establishment of a new population on an island offers plenty of scope for research. Jildou and Peter will be investigating the warbler’s population growth since 2007 and undertaking a detailed survey to ascertain survival and reproductive success in the population. Jildou and Peter are working under the supervision of Dr Jan Komdeur who worked in Seychelles for several years in the late 1980’s and early 1990’s. Jan was the man responsible for the propagation of the warbler to other islands that has done so much to enhance the conservation status of this endemic species. His detailed research of the warbler and its habitat requirements enabled the transfer of birds from the then sole colony on Cousin island to the islands of Aride and Cousine and latterly Denis.
Jildou and Peter are looking in particular at female mortality. There is evidence from the previous Denis survey in 2007 that the warbler population was skewed, with more males than females. Birds on a new island with abundant vacant habitat undergo more rapid reproduction than they do in established populations simply because resources are more abundant. Breeding is an energy intensive activity particularly for the females. It is postulated that this investment by the females may detract from their longevity and hence the development of a skewed sex ratio in the population.
Jildou and Peter will therefore be monitoring levels of stress in the birds by taking blood samples and checking for levels of oxidative stress, they will also be looking at the level of stress hormones in warbler faecal samples. They are furthermore looking at the levels of immunocompetence in the birds by assessing a variety of physical characteristics of the birds – as stress can affect immunocompetence.
This research is very interesting and has various ramifications for the planning of bird translocations in the future. From a Denis viewpoint, we are particularly interested in an update on the status of the population, its distribution and habitat use as this will help inform decision-making with regard to vegetation management on the island.
Keep checking back for more updates on Jildou and Peter’s endeavours.
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