Thursday, 5 December 2019

Grounded by the light

Skomer island has a massive part to play in the success of an enigmatic seabird often hailed as Wales' national bird. Every year half the world’s population of Manx shearwaters, that's around 700,000 birds, make the 7,000 mile journey from South America to breed on this tiny Pembrokeshire island. Thousands more breed on neighbouring Skokholm and Ramsey islands. It is a big responsibility to ensure these islands remain a safe place for these birds to rear their chicks. Biosecurity measures to prevent invasion by predators such as rats and mice is paramount. That is why we ask you to check your bags when you visit. It is also important that we give the young birds the best chance of fledging successfully so that in future years they will themselves return as breeding adults.

The Pembrokeshire islands: Skokholm (left) Skomer (centre) and Ramsey (far right)

Adult Manx shearwater gliding effortlessly over the sea 
700,000 birds come back to breed on this island every year

Research on Skomer by the OxNav group has shown that fledging birds can be significantly disorientated by light pollution which causes them to become grounded on-shore rather than heading far out to sea and safety. Unfortunately, the chicks having spent their entire life to this point in the darkness of an underground burrow have not yet learnt how to avoid the hazards of the bright lights. Everyone who stays overnight on Skomer uses red light to walk around at night so we don't disturb the birds.

During the fledging season (late August to late September) many chicks are blown off course by stormy weather and further disorientated by bright mainland lights. They become grounded inland or on off shore tankers. OxNav PhD student Martyna Syposz is currently researching this phenomenon on Skomer and her paper on the effect of light pollution on fledging Manx shearwaters in Scotland can be read here.

Martyna weighing a Manx shearwater chick on Skomer

Very young Manx shearwater chick being weighed (Photo Viv Hastie)

Manx shearwater fledgling exercising its wings before heading out to sea
Manx shearwater close to fledging in it's underground burrow (Photo taken from Skomer's burrow cam)

For the past two years, a joint project involving the RSPB and WTSWW has led to a campaign aimed at increasing public awareness about this issue. This campaign has also recruited volunteers across Pembrokeshire to rescue and release grounded birds back out to sea. Manx shearwaters should never be seen over land, let alone grounded, but many have been found stranded in gardens or on roads in Haverfordwest, Carmarthenshire and even as far as Ely in Cardiff! Highly adapted for a life at sea, once grounded on land Manx shearwaters struggle to take flight and without rescue would surely die. This has been an incredibly successful campaign and has led to the rescue of hundreds of birds and importantly highlighted the plight facing these young birds. 
Rescued Manx shearwater fledgling awaiting release at night (Photo: Thousand Islands Expeditions)

What we now need is to go one step further and we would love to see light pollution around the Pembrokeshire islands reduced during the fledging season. Those of you that have stayed overnight on Skomer this year will have noticed we now have blackout blinds in the hostel so that our birds are not affected by night time island lighting on the island. This simple intervention has led to a dramatic decrease in birds grounded in the farm courtyard.

Procellariifromes, the group of birds that include Manx shearwaters are amongst the most threatened of all seabird species, primarily due to climate change and over fishing and pollution. The last thing they need is another hurdle to get over. It really doesn’t have to be that difficult to fix this problem. For one month of the year surely we can turn those lights down for the fledglings.

Sarah Parmor (Skomer Visitor Officer)

Friday, 15 November 2019

Are there any bats on Skomer?

Hi everyone, it’s LTV Rob here! I’ve been off the island for just over 4 weeks now and am missing it a lot, so I thought I’d give you an update of the project I carried out whilst there.
Abseiling into caves for seal monitoring gave me an opportunity to check out potential sites for bat roosts.
One of the animal groups on Skomer that really intrigued me from the outset were bats. With no trees on the island, there appears to be little suitable roosting habitat – so are there bats there? The most recent survey of the island was conducted in 2014, but this was only at The Farm so I was keen to look at activity across the island.
I used an SD1 recorder for the study. These amazing bits of kit can be pre-programmed to record at certain times of day. During active hours, the recorders ‘listen’ for sounds of certain frequencies. When it identifies what it thinks is a bat it records a sound-bite which can then be downloaded later. These recordings are viewed on spectrograms which are visual representations of the calls. Each species has a unique call shape which allows us to tell them apart.
If you visited the island from July to September, you might have noticed my bat detector setup – it looked a bit like some sort of NASA Moon lander! The microphone was tied to an old tripod which meant I could set it up at different locations on the island – The Farm, Moorey Mere, North Pond, North Haven, North Haven Slip, on the main track towards the courtyard and overlooking The Lantern, a large cave system on the very east of the island. I left the recorder for several days at each site and then collected it in to see what we’d got…
The bat detector set up at the Farm

The detector enjoyed some nice views of Middleholm from the 'Lantern' (and strong winds too!)

Over the 7 recording sites, 380 bat recordings were obtained. 6 species were identified with confidence: Common Pipistrelle, Soprano Pipistrelle, Leislers, Noctule, Serotine and Greater Horseshoes. Barbastelle and Grey Long-eared bats were also suspected. This is a good result for Skomer as it suggests that bat diversity is stable. Activity varied between sites for each species, which suggests that species are utilising different areas of the island.
Perhaps the most exciting finding is that of Greater Horseshoe bats! This rare cave-roosting species has declined nationally by over 90% in the last 100 years and is restricted largely to a few populations 
in south-west England and Wales. This is partly due to the intensive use of pesticides which are reducing prey availability. 58 recordings of Greater Horseshoes were taken across the island, which is higher activity than was seen in 2014 – this could suggest that Greater Horseshoe numbers are on the rise on Skomer, which is very encouraging. Islands like Skomer, which is pesticide free, are evidently a natural stronghold for them!
Greater Horseshoe bat (source: Bat Conservation Trust 2010)

A spectrogram of the Greater other species call at 80kHz so I knew immediately what it was!

This project highlighted that there is high bat activity on Skomer and that species activity varied between different habitats on the island. More work is needed to understand how each species is using the island so watch this space! In the meantime, next time you visit Skomer think about these flying mammals which are hidden away during the day and come out to join the Manx Shearwaters after dark…
Thank you for reading my batty ramblings!
Rob (Skomer LTV 2019)