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

• 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.

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.

Sooty tern update…

Part of the island’s management plan is in effect about turning back the clock. The southern portion of the island has been identified for restoration. The long term goal is to take this area back, as close as we can, to its original state when first discovered by man. De Trobriand the discoverer of Denis in 1773 left us a fascinating and quite detailed description of the island and its wildlife.

One of the dominant seabird species found on Denis at that time was the Sooty Tern (Onychoprion fuscata). Today one of the first aspects of restoration we are broaching is an attempt to re-establish a breeding population of Sooty terns on the island. Whilst we do not have specific records on the history and fate of the original sooty tern colony, we can draw certain conclusions from the island’s known development history and it seems probable that the bird has not successfully bred on the island for some 150 years.

We are now into the second year of this project and as such work has never been previously undertaken with the Sooty tern we are breaking new ground and learning as we go along. In this second year we have refined our approach following the results of last year and it has definitely been more successful (Previous posts cover the earlier stages of the project see: 19/05/09 and 02/07, 21/09 & 13/10 2008).

The sooty tern project was the focus of much my attention during my last visit to the island and it was most encouraging. On the Thursday afternoon I observed a few birds circling and a couple on the ground but it was on the mornings of Friday and Saturday that things were much more interesting. GIF volunteers Vicki and Georgia have been working steadily on the project and I hope that one or both of them will post soon on their perspective on the project. Both of them were present on Friday morning and the project area was alive with activity. Up to 37 birds were to be seen on the ground at a time with many more circling low over the area and calling. The birds on the ground were observed courting and mating and interacting as if a colony was under formation – it was fascinating stuff. The occasional bird was still seen to attempt to mate with one of the models as well. The next morning was much the same with up to 35 birds being observed on the ground at any time this time with the birds in general occurring in a single group.

It is unlikely that we will see any egg-laying on the island this year as, despite the delay in the onset of the southeast monsoon, egg-laying commenced in the existing Sooty colony on Aride Island in early June. Nevertheless the results this year are much improved from last and we continue to learn more about the bird’s preferences and how we might better design the project next year. According to studies the Sooty tern does not return to breed until it is 6 or 7 years old so it may well be that the birds we are attracting are young adults that are reconnoitring potential breeding locations for next year – let’s hope they keep Denis in mind!!!

Southeast monsoon.

Flying to Denis on Thursday 16th July it was clear that the southeast monsoon was blowing strongly and had finally, properly established. Seychelles has two seasons determined by the direction of the prevailing wind either the northwest trade winds or the southeast monsoon. The southeast monsoon has been very late establishing this year and this affects the habits of many animals notably the breeding activity of seabirds that rely on the seasonal winds and related currents to bring the small fish they need to breed and successfully raise a chick.

I hadn’t been to Denis for a couple of weeks and last time I was there the southeast was blowing intermittently. On Thursday the white caps of waves were visible throughout the flight from Mahe to Denis. As the plane descended and approached the island, choppy water was evident on the surrounding shoals and then I saw something that I have never previously seen. A plume of sand was being carried offshore from “Pte Mme Guichard” on the northwest point of the island, off the shoal and into deeper water.

I have been monitoring the cycles of sand movement on the northwest coast since December 2005 and there is definite evidence of erosion. The difficulty in assessing such changes however is the fact that there may well be ongoing long-term cycles of erosion and accretion for which we have no information. It is therefore not possible to see short term changes in coastal profile in the proper context. Such thoughts are further complicated by ongoing changes in global weather patterns and the related issue of sea level rise. It is important however to monitor trends in coastal erosion in particular on the shoreline where key infrastructure is located in order to inform management decisions.

On seeing this sand plume going offshore and into deeper water it occurred to me that such sand loss may be permanent. Normally when I fly into the island I have camera ready for in case of a good photo-opportunities but on this trip because of the cloudy weather and poor light I hadn’t bothered. So I had to scramble to get the camera and snap some shots… so not great but good enough to show the occurrence… see photos in sidebar.

There was further evidence of the onset and stabilisation of the wind on the island. The sand promontory at Pte Mme Guichard has been largely eroded – a usual part of the island’s beach profile dynamics. I had reported previously (see post of 8th May amongst others) about the recovery of vegetation a Belle Etoile on the east coast following the cessation of grazing cattle there. This had greatly changed the view of the area with the former open meadows and casuarina-framed vistas obscured by the dense growth and foliage of papaya thickets. Well the salt spray driven by the “southeast” wind has changed this dramatically the leaves are gone leaving the barren stems to point accusingly at the sky.

Another key issue related to the southeast monsoon is that it will also mean that the Sooty tern season should get properly underway… but that is the subject of another post…

Shells 2: The Minstrel Cowrie - Cypraea histrio

On Tuesday the 18th of November I posted on the mollusc Trochus virgatus and now, having not been to the island for a couple of weeks, seems to be an appropriate time to continue that theme.

During November we had some good high tides and wave action that served to wash up quite a few dead shells from the surrounding reef flats. At the same time I found the T. virgatus I also found a good specimen of the Minstrel cowrie (Cypraea histrio). The pictures below show the specimen of this beautiful species of sea snail and can be enlarged simply by clicking on them.

Jarrett (2000) states that C. histrio is very common in Seychelles where it occurs in shallow waters and rarely deeper than 3 metres.

Ref: Jarrett, A.G. (2000). Marine Shells of the Seychelles. Carole Green Publishing, UK.

Day geckos (Phelsuma astriata and Phelsuma sundbergi)…

Visitors to Denis will all notice the bright green geckos that can be seen on the trunks of coconut trees and at night on the columns in the restaurant – where they lie in wait by a light to capture the insects it attracts.

There are in fact two species of day gecko to be found on the island the Lesser day gecko (Phelsuma astriata) and the Day gecko (Phelsuma sundbergi). Both species are endemic to the granitic Seychelles but are believed to have both been introduced (presumably inadvertently) to Denis. Gerlach (2007) states that P. sunbergi was first recorded on Denis in 1908 whilst P. astriata was introduced as recently as 1981. Of course lizards can and are known to colonise distant islands via floating vegetation so such matters are never entirely clear cut but the apparent recent nature of these colonisations does very much suggest a human vector. Regardless both of these species are now well established on the island and as species endemic to the central archipelago are more than welcome.

P. sundbergi is the much larger and heavier set species (getting up to about 20cm long including its tail) when mature and tend to be territorial. Typically one will be evident per coconut trunk or column on a boat shed or verandah and when two occur they will often be seen to fight. They are particularly noticeable to visitors as it is this species that populates the columns around the restaurant. They are typically bright green with on closer inspection, a light red freckling on the back of some individuals.

P. striata is significantly smaller (10 -12 cm including tail) and much less sturdy in build than P. sunbergi and can be seen on vegetation, tree branches, palm leaves and also on walls. It has visible pale belly and interesting red patterning on the bright green of its back and head. The adult has a distinctive red chevron on its head typically followed by two transverse bars on its neck (see photo in sidebar – this specimen has dots rather than the bars but it was a juvenile and the bars may form later). They typically have a spinal red line with patterns of red dots. On Denis these dots often merge to form a herringbone pattern (see sidebar). Occasionally a black P. striata can be seen this colour change is a reversible defensive stress response.

The Palm Spider (Nephila inaurata)

Arachnophobes need read this post no further – but of course do scroll down to other posts! - as this spider fits the bill as a pretty frightening beast if you are that way inclined.

The Palm spider (Nephila inaurata), also known as the “red-legged golden orb-web spider”, can get pretty big. I have seen them, including leg span, soup dish-sized and building their webs from the telephone lines to the ground in the south of the main island of Mahe!

They are fairly common throughout Seychelles and on Denis can typically be seen in their webs along forest paths. The spiders themselves are harmless – unless of course you are an insect – and during fieldwork I have often accidentally walked through a web and had a spider scrambling over me, generally doing the best it can to get off as quickly as possible.

Their webs are strong and are reputed to be able to ensnare even small birds though I have never observed such an occurrence. The large spider at the centre of the web is the female whereas the male is very much smaller and can often be seen nearby typically on the other side of the web (see photo in sidebar). I am often asked and do not have the answer for whether the female eats the males – I don’t think so – but it may be for good reason that the males are typically found on the other side of the web!

I have dithered as to whether to do a post on the palm spider for fear of putting off people from visiting the island. This however is the tropics and visitors to such destinations should expect to find life teaming in all forms. Seychelles in fact has very few creepy-crawlies when compared to tropical continental landmasses and none of them are dangerous. In the case of this spider it remains stationary in its webs in the forest and is not one that you need worry may come and visit you in your room. So don’t be put off, the Palm spider is in fact a very interesting species fulfilling its role and occupying its place in the island ecosystem.

White tern (Gygis alba) rescue

The white tern (Gygis alba) is an unusual bird in several respects. In particular it does not build a nest but rather lays its egg in a hollow or fork of a branch. This requires some particular adaptations by the chick in particular the ability to anchor itself to the branch with its claws even before properly emerging from its shell. Chicks therefore have well-developed feet and claws whilst the rest of them is little more than a fluffy ball of feathers.

The strength of its claws was brought home to me a couple of weeks ago on the island whilst taking some tour operator representatives on a tour round the island. I was actually looking for a Seychelles warbler that I had just heard when I looked up to see a white tern chick hanging upside down from a branch. I initially thought the chick was dead but then I saw an adult sitting on the perch above and looked more closely at the chick. It was alive with breathing and eye movement evident and hanging by just a couple of claws of one foot… not a good situation.

The bird was a good 15 feet off the ground up a spindly ornamental tree near the main hotel complex. I went in search of a ladder and on my return, having with the assistance of some of the tour reps worked out how to properly extend it, still found the ladder too short for someone of my limited climbing capacity to reach the bird. Fortunately a young man from the garden staff was walking by and I asked him if he would be able to help. He took one rather dismissive look at the ladder, and proceeded to shin agilely up the tree retrieved the bird and replaced it on the perch where the adult had been!

I had been too preoccupied to get a photo of the chick whilst it hung precariously, but one of the tour reps, Amy Pearson, did get a shot of the rescue which she has kindly sent to me (see sidebar).

I went back the next week to check on the chick and found it well and on its perch - so a nice little feel-good story for all involved!

The “Sally Lightfoot” crab or Karkasay (Grapsus tenuicrustatus).

I have previously posted on the importance of hermit crabs in the island ecosystem (see post of 16th July 2008) and the work we have undertaken to look at the occurrence and populations of the three species that occur on the island.

Denis, of course, has other crabs of both land and coastal species and in this post I will focus on the “Sally Lightfoot”, known locally as “Karkasay” (Grapsus tenuicrustatus) which is a crab of rocky shores. It is interesting that the species occurs at all on Denis as the island is a sand cay without rock. Denis was formed during the last glaciation when sand piled up on a patch reef that today forms the reef flats around the north, east and south east coast of the island and can be considered, in some respects, as the “backbone” of the island.

The “rocks” that are to be found around Denis and that form the habitat for G. tenuicrustatus are in fact made of sand! A large part of Denis’ surface area is today actually made up of sandstone. Sandstone that was formed from the action of acids, leached from millennia of sea-bird droppings, acting to bind the coral sand particles together. There are in fact two layers of sandstone on the on the island suggesting that it may have been submersed at some point in its history before re-emerging above the waves.

This sandstone is not particularly strong – it being possible to break fragments of it by hand – it does nevertheless form a solid structure against wave action and can be found forming extensive wave-smoothed tablets along the east, south and south west coasts of the island and distinct outcrops at the southern point of Denis. This therefore is what provides the habitat for a rocky shore crab on an otherwise sand cay island.

G. tenuicrustatus is a herbivore that grazes on the algae that grows on rocks on the coast. Its sleek highly streamlined form, necessary for it to cling to rocks as waves break, gives it an almost alien appearance when seen in profile. Research elsewhere (Martinez 2001) has shown that a very minor shift in stance of the crab greatly reduces its drag in water and enables it to withstand 200% faster flow of water without being dislodged.

The Karkasay on Denis are alert and wary of intrusion, very swiftly retreating into crevices or if necessary jumping into the sea when someone approaches. Clearly this is a predator avoidance technique and though I have yet to sea anything predate them I imagine visiting herons and the ever present conger eels pose a threat - not to mention of course man, seeing as Karkasay make a good curry!

I was able to get some good shots of the crabs on the south and southwest coast (see sidebar). Of particular interest was that the crabs did not retract their eyes at the moment a wave hit, further evidence of their adaptation to the coastal environment.

Sometimes what appears to be a pink-red corpse of a crab can be found intact on the rocks – this is in fact an exoskeleton shed by a growing crab.

There are several other species of crab to be found on Denis and I aim to cover them in future posts…


Ref: Martinez, M.M. (2001). Running in the surf: hydrodynamics of the shore crab Grapsus tenuicrustatus. Journal of Experimental Biology, 204, 3097-3212, (2001).

Focus on the Seychelles Turtle Dove (Streptopelia picturata rostrata/picturata)

A lot has been written about the Seychelles turtle dove (S. p. rostrata) and its progressive demise by cross-breeding with the larger and introduced Madagascar turtle dove (S. p. picturata). Although there is no real consensus the general view is that Madagascar turtle dove was introduced probably as a released food supply by a calling vessel in the mid-19th century - though Beamish (1981) states that it was introduced as recently as the early 20th century.

The Madagascan race is larger than the endemic Seychelles race and males compete for access to mates. The males face off side to side and jump and bat their near wing on the ground in aggressive displays. Feathers puffed out, back arched and outer wing raised they attempt to intimidate their opponent by the impression of greater size. If this does not work, then fighting can ensue with the birds then hitting each other rather than the ground with their wings until supremacy is established. The advantage is clearly with the larger bird resulting in more successful breeding by the Madagascan males and the spread of their physical characteristics through the population.

Some authors go into great detail describing fine differences between the phenotype of the two races for the purposes of this post however; Penny’s (1974) description will suffice:

“ Rostrata has a vinous red head, a chestnut mantle, grey brown under tail feathers and is much smaller”

“Picturata has a grey head, purplish mantle, white under tail and is larger”

For many years it was reported that individuals exhibiting the rostrata phenotype were restricted to the small islands of Aride, Cousin and Cousine. Penny (1974) also cites Fregate which makes sense as though not small it is the most isolated of the granitic islands.

Whilst working on Cousine Island in the mid-nineties I undertook a survey of the turtle dove population on the island. I caught, if I recall correctly, some 120 birds and scored them on various characteristics from plumage colour on various parts of their bodies, eye colour and various biometrics including wing length. Each bird measured was ringed to avoid repetition. At the time my results suggested that 1 in 3 turtle doves on the island still exhibited strong rostrata characteristics. I still have all the data in an old logbook at home one of several topics that fit into the likely doomed “I must write it up someday category…”

In 1995 Chris Feare – yes the same Chris Feare who is now working with us on the Sooty tern project – published a brief paper on his findings of turtle doves on Bird Island. Where, though admittedly with a small sample, his capture and grading of the birds suggested a population very close to the rostrata phenotype. Feare goes on to suggest that a small number of birds were either introduced or colonised naturally in the latter half of the 19th century and had persisted there largely unnoticed until changes in vegetation in the latter part of the 20th century allowed the population to increase.

Although not mentioned in the literature (indeed Hill 2002 states that the birds on Denis are of the picturata form) I have found there is definitely considerable variation in the physical characteristics of the doves on Denis (see photos in sidebar) and though I have not gone to the lengths of capturing and scoring the birds physical traits (too many more important and pressing issues to address) I think the population on Denis may be of interest in that regard.

This is notable because if the population on Denis were scored for its phenotype and then managed over a period of years it may be possible to bring back the endemic rostrata phenotype throughout the population. This due to Denis’ relative isolation could be maintained with just periodic monitoring and management.

A project for the future perhaps…

Refs:
Beamish, T. (1981). Birds of Seychelles. Dept of Agriculture. GoS.
Feare, C, J. & E.L. Gill (1995). The turtle doves of Bird Island, Seychelles. Bull. B.O.C. 1995 115(4).
Hill, M.J. Ed (2002). Biodiversity surveys and conservation potential of inner Seychelles islands. Atoll Research Bulletin. July 2002.
Penny, M. (1974). The birds of Seychelles and the Outlying islands. Collins. ISBN 0 00 219829 0

Sooty Tern Update – encouraging progress!

Apologies for the delay in posting but paperwork deadlines have kept me very heavily occupied over the last 10 days – here’s hoping the effort pays off!

I paid a 24-hour visit to the island, weekend before last, in order to show some representatives of a potential donor agency the ongoing environmental work on Denis and also highlight some aspects that may be of interest to their organisation.

I made a special effort however to follow up on the sooty tern project during the visit and see how work is progressing and have some very encouraging news to recount.

I observed several birds circling very low over the project area and calling and also observed 3 birds landing. As we have seen before single birds that land, bow and display to the models but of course the models do not respond. However when they land in groups they can display to each other and this is our hope that sufficient birds can be attracted simultaneously down to the site such that they can cross-stimulate each other and begin the formation of a breeding colony.

That day though, I was particularly interested in the behaviour of one bird that appeared to be exhibiting “scrape-making” behaviour. This is the precursor to egg laying and of course a very exciting development for the project. The bird stayed on the ground for more than 40 minutes and was twice attended by another bird – perhaps its mate? See photos in side bar which, although somewhat overexposed (it was a very bright sunny day) and taken at the maximum zoom nevertheless, serve to show the birds on the ground in amongst the models. The bird was down on its chest and displayed the rocking side-to-side motion that accompanies the activity of making a scrape in the ground that it will later lay in. I was not though, due to the lie of the land, able to see whether the bird’s feet were in fact scraping at the ground in order to make a depression. Notably having a left a bird (presumably the same one) did later return to the exact same location. So fingers crossed!

That however is just the least of it! On the morning of Wednesday the 24th June I received a call from the volunteers advising me that 20 birds had been on the ground that morning and that they had observed 3 pairs mating. This is very encouraging and caused me to advise several interested parties including Prof. Feare in UK accordingly.

We are of course still learning as we go; such a project has never been attempted with Sooty terns before and we are continuing to refine the methodology as we progress. These developments however constitute a major advance and give us hope for the future even if this year we do not have birds attempting breed on the site.

Time will tell… check back regularly for updates.