Lighthouse Journal

Sunday, February 13, 2011

A tree next to a swing bridge at La Selva was probably the best tree of the holiday. That's because, in the brief periods in which no-one was walking across it (causing it to bounce and swing from side to side), six bats could be seen clung to the bark in the shade. They were exceptionally well camouflaged, and you had to know where they were to see them.

The Best Tree in Costa Rica (c) Richard Brown

Greater White-Lined Bats (c) Richard Brown

Again I (Giselle) was very excited by these bats. Reason the first; in England I have never observed bats hanging on the outside of trees in the daytime. Reason the second; in England, bats do not have crazy white parallel lines running down their backs.

So what are they? Out of 110 species of bat officially recorded in Costa Rica, we whittled these critters down to the title of Greater White-Lined Bat. It wasn't too difficult, as our guide told us what they were.

They belong to a family called 'Sac-Winged Bats' and are insectivores with wing-sacs. Whats the point in having a sac on your wing? Well, the sacs are used socially as scent marking organs.

During the breeding season, individual colonies are defended by one male. To attract a female the male emits a scent from his wing sacs. This is accompanied by a complex song which he performs whilst hovering in front of her. Awesome.

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A few things that will make this blog make more sense:

What is a Lighthouse attraction?

It is perhaps surprising how many bird species move nocturnally. Huge numbers of waders, thrushes and warblers are joined by birds such as shearwaters, petrels, rails, terns, larks and starlings. The majority are relying in a large part on the visible night sky to aid navigation and on light, particularly from the moon, illuminating the landscape. If bad weather descends whilst they are on the move they use other features to orientate themselves. The beams of Bardsey Lighthouse, which officially reach up to 43km out to sea, are particularly attractive if other navigational cues are absent. Up to 31,573 birds have descended upon the Lighthouse in a single night. Sadly some of these birds fatally collide with the light, typically Manx Shearwaters and thrushes, but also species such as Thrush Nightingale and Red-eyed Vireo. We are based at the light to monitor these attractions, help to direct birds away from the tower using gantry lights and catch grounded birds to stop them again flying at the light. The lighthouse plays an important role in shipping.

A bit about Bardsey’s migrant birds

Bardsey has played host to the first Summer Tanager and Yellow Warbler to be recorded in Britain or Ireland. Additionally American Bittern, Sora, Black-winged Stilt, Killdeer, Spotted Sandpiper, Lesser Yellowlegs, Penduline Tit, Lanceolated Warbler, River Warbler, Booted Warbler, Blyth’s Reed Warbler, Grey-cheeked Thrush, Eyebrowed Thrush, American Robin, Thrush Nightingale, Red-flanked Bluetail, Isabelline Wheatear, Black-eared Wheatear, Collared Flycatcher, Blyth’s Pipit, Olive-backed Pipit, Song Sparrow, Dark-eyed Junco, Pine Bunting, Rock Bunting, Yellow-breasted Bunting and Blackpoll Warbler have all been recorded. Rich has found the second Paddyfield Warbler and White-throated Sparrow for Wales (the first White-throated Sparrow was also on Bardsey), along with good Welsh birds such as Short-toed Lark, Icterine Warbler and Pallas’s Warbler. In recent years we’ve had Glossy Ibis, Black Kite, Woodchat Shrike, Greenish Warbler, Western Bonelli’s Warbler and Ortolan Bunting and species such as Melodious Warbler and Subalpine Warbler are more than annual (the eastern race of Subalp is a particular Bardsey speciality).

A bit about bird ringing

Ringing is a method which has been used for over 100 years to study birds. It has proven very successful because the individually numbered rings make no difference to the behaviour of the birds. Bardsey Bird and Field Observatory has been ringing since 1953. A mass of information has been gathered relating to many aspects of avian biology including movements, physiology and longevity, all of which help us to understand and conserve birds. Some of the multitude of interesting Bardsey records include:

On the 8^th May 2008 we retrapped the Manx Shearwater FB10565. It had first been ringed as an adult on the 17^th May 1957, 50 years 11 months and 9 days previously. This is the oldest known wild bird in Britain.

Bardsey has also hosted the oldest Razorbill, at 41 years 11 months 23 days, the oldest Wren, at 7 years 3 months 10 days and the oldest Chough, at 16 years 8 months 26 days.

We get many records each year of birds ringed elsewhere arriving on Bardsey or of our birds turning up. Recently Manx Shearwaters have been recorded in South America within a few weeks of departing their burrows, our other seabirds have reached various colonies elsewhere in the UK and Europe and our Lesser and Greater Black-backed Gulls have been recorded in Spain, Portugal and Morocco. Waders such as Whimbrel and Sanderling have passed through from the Arctic and Iceland. Migrant passerines include Sedge Warbler and Chiffchaff to Senegal and a Starling from Lithuania.

Movements are often rapid with several hundred kilometres being covered in a few days. Just in the last few years a Reed Warbler arrived from Belgium in 17 days, a Willow Warbler reached Lands End in four days, a Song Thrush reached Spain in 56 days and a Blue Tit reached Cape Clear in 19 days.

We ring birds under licence from the British Trust for Ornithology. Their website gives lots of info about ringing: http://www.bto.org/volunteer-surveys/ringing/about. This is also the place to go if you discover a bird with a ring on its leg.

A bit about birding Bardsey

The Lighthouse As mentioned, this is where we live to monitor birds attracted to the light. Anything is possible and sometimes masses of birds descend on the area. Rarities at the light have included Thrush Nightingale, River Warbler, Grey-cheeked Thrush and Red-eyed Vireo. We’ve seen two hundred Grasshopper Warblers here and a Little Egret hovering above our heads.

The South End Seas of Thrift and not much in the way of cover mean that this is a specialist habitat. We’ve seen Short-toed Lark, Dotterel and Quail on the deck but it’s the overhead vis mig which is best as birds funnel to the tip to cross the Irish Sea. The few patches of Gorse hide grounded migrants, many of which will have been attracted to the light.

The Narrows The narrowest part of Bardsey and home to Solfach and Henllwyn, a small sandy beach and a larger rocky bay. The best place to look for waders and where any storm-blown seabirds rest. Also another vis mig funnel. Recent highlights have included Baird’s Sandpiper, Avocet, Sabine’s, Glaucous and Iceland Gulls and Hoopoe.

The Badlands Named by ME and full of possibilities. Wellies are often a must as we tramp for Jack Snipe, Snipe, Woodcock and Short-eared Owls through rushes and bog. Patches of Gorse provide breeding habitat for Linnets and Stonechats.

The Withies and the Green Lane Five main patches of predominantly Willow and Reed linked by hedge-lines, they have a very impressive list. Recent highlights have included Rich’s Paddyfield Warbler along with multiple Icterine and Melodious Warblers. Historical highlights have included American Bittern, Sora, Summer Tanager, Yellow Warbler, Arctic Warbler, Aquatic Warbler and Penduline Tit.

The Gardens Away from the Obs there are 11 mature gardens which all need grilling in search of grounded migrants. Anything could occur, from a Red-flanked Bluetail at Ty Nesaf to a Wryneck at Carreg Bach.

The Observatory A mature garden of Damson and Gorse and our main ringing site. Subalpine Warbler and the commoner Hippos are annual and usually trapped. This is the place in the UK where Subalpine Warblers are known to have progressed furthest in a breeding attempt. Seawatching from the terrace is a real possibility and the kettle is never far away.

The Plantation A belt of older conifers are flanked to the North by a new plantation of scrubby natives. The sheltered side is often the favoured haunt of Flycatchers, including Gis’ R-b Fly in 2011, and the main plantation contains the bulk of our migrants in a good fall when hundreds of Phylloscs and crests can litter the branches and floor. The nearby withy and hillside have harboured some stunning birds, recently including White-throated Sparrow, multiple Barred and Pallas’s Warblers, Western Bonelli’s Warbler, Common Rosefinch, Corncrakes and Greenish Warbler.

The West Coast Perhaps under-covered as the Withies lure birders inland. This is a beautiful stretch of coves and short grass home to Choughs, Wheatears, Rock Pipits and Oystercatchers.

The North West Fields Not just a great area of maritime heath, a lure to scarcer buntings and pipits, but also home to the best seawatching hide on the island. This is where seabirds pass closest and in a good Northwesterly the views and diversity can be belting. The scarcer passage seabirds such as Long-tailed Skua, Sabine’s Gull, Grey Phalarope and Leach’s Petrel are regular at the right times.

The Mountain Often under-covered as it leads the birder away from some other cracking areas, however the mountain is the place to pick up Snow Bunting and is the main fly way for passage raptors which go through rapidly. We’ve recently seen Hobby, Ospreys and several Marsh Harriers as they go through.

Anywhere Else There could be an Ortolan Bunting in the track or a group of Crossbills drinking at a puddle. Anything could pass over with Black Kite, Glossy Ibis and Richard’s Pipits all recorded overhead in the last couple of years.

A bit about Bardsey’s breeding birds

Manx Shearwater There are somewhere between 9000 and 16000 pairs on Bardsey. They usually arrive back in mid March, established pairs returning to the same burrow as in the previous year. After mating the female nips off to form the egg, perhaps to Biscay, whilst the male defends the burrow from other prospecting pairs. They then take turns incubating the single egg for around 52 days and then provision the downy chick for a further 70 days or so. Productivity is usually between 0.70 and 0.88 (2002-2011 average 0.77±s.e.0.02) and was 0.73 in 2011. To avoid predatory birds the Shearwaters only come and go when it’s really dark.

Storm-petrel This is a difficult species to monitor as the colonies are restricted to the treacherous East Side. The birds only return at night meaning that to count apparently occupied crevices during the day is the best way to assess numbers. This is done using a tape-playback of their song to elicit responses from incubating adults. Due to the amount of work involved we don’t count them every year, but in 2002 there were thought to be approximately 35 pairs. Their distinctive smell alerts us to their continued presence each year when we are working in the Razorbill colonies. To see them on Bardsey you need to be present for one of our summer ringing sessions.

Oystercatcher One of our most conspicuous breeders with most of the accessible coastline holding alarming pairs during the breeding season. They are by far the most abundant breeding wader with 85 pairs on territory in 2011, nine fewer than in 2010, but 6.4% more than the 2002-2011 mean (79.90±s.d.12.13). In 2011 52 nests were located. They contained 141 eggs or a mean clutch size of 2.71. Of the 52 monitored nests, 31 failed at the egg/small chick stage, nine failed with chicks and 12 were successful. Predatory gulls and corvids account for many of the failures. A total of 14 chicks fledged from the successful 12, which gives a productivity figure of 0.27 chicks per pair, 25% down on 2010 and 65.4% lower than the 2002-2011 mean (0.78±s.e.0.20).

Ringed Plover In 2011 breeding occurred for the second time since 2003 following two pairs that successfully fledged seven young in 2010. A clutch of three eggs near Solfach on 28 April were covered with a chicken-wire cage to protect them from sheep and predatory birds whilst leaving just enough room for the adults to slip underneath to incubate. This worked well last year and again proved fruitful with all three newly-hatched young ringed in the nest on 22 May. A week after all three young had fledged a further four eggs were discovered in the same covered nest on 28 June. Three newly hatched chicks were ringed on 19 July with the fourth egg failing to hatch. All three had fledged by 20 August. A productivity figure of 6.00 was the highest recorded on Bardsey.

Guillemot This species famously defends the smallest territory of any bird. They have many adaptations for living close together. They recognise their neighbours, which they will tolerate at close proximity, and they have eggs with very diverse patterning so they can recognise which one is theirs. The eggs are extremely conical so they role in a very tight circle. In 2011 981 adults on ledges were recorded, a figure almost identical to 2010, 24.7% more than the 2002-2011 mean (787.00±s.d.156.67) and 116.6% more than the long-term mean (453±s.d.225). Productivity was 0.30 fledging sized chicks per pair.

Razorbill This is the largest auk in the world and one of the commonest seabirds on the East of the Island. The pairs mate for life but will not breed until about five years of age. They’ll mate about 80 times at the start of the breeding period to ensure fertilisation and then incubate the egg for roughly 35 days. The incubating birds are hidden away in crevices and caves which makes counting them difficult. Over 1500 adults were counted around the colonies in 2011. The chick only stays ashore for about 20 days before swimming out to sea with the male. The sea is a safer place to be with so many predatory gulls around.

Little Owl This diminutive owl was introduced to the UK in the 19th century. On Bardsey a minimum of three territories were recorded in 2011. A pair nested in a field boundary to the South of Carreg Bach where two chicks were ringed on 5 June. Both had fledged by 28 June. Additional pairs were to the South of Cristin and near Rhedynog Goch, but neither was proven to breed. Pellet analysis has shown that invertebrates and small birds make up the bulk of the diet although we have not recorded the predation of Storm Petrels seen on other Welsh islands.

Skylark In 2011, three pairs established territories, one in the North West Fields, one East of Nant Valley and one in the West Coast Fields. The West Coast pair produced five eggs, all of which hatched. The five pulli were ringed on 18 May, 18 days earlier than they were ringed in 2010. All fledged in early June. A second brood was suspected but no fledglings were recorded. The Nant Valley pair had fledged at least one chick by 29 May. The North West Fields pair was present throughout the breeding season but no fledglings were observed. This is the best showing since 2005 and the most fledged young recorded since the recolonisation in 2003.

Swallow Nationally this species has undergone a long-term decline in the UK but numbers fluctuate widely. On Bardsey in 2011 the number of breeding pairs was 21, 56.7% more than the 2002-2011 average (13.40±s.d.4.58), and the most ever recorded (equal with 2008). A total of 106 birds fledged from 31 broods, the most fledglings ever observed. Productivity was thus 44.3% up on last year and 6.8% above the 2002-2011 mean (4.73±s.e.0.48). Disappointingly at least nine juveniles were found dead within a short period after fledging. Climatic changes in the African wintering grounds mean that birds are returning to Britain in poorer condition and laying fewer eggs than previously recorded.

Chough This is another species which shows strong mate and site fidelity. A record eight pairs attempted to breed in 2011 with a ninth pair prospecting suitable sites but not attempting. Disappointingly two pairs nesting on Mynydd Enlli failed. Of the remaining pairs, one fledged four, one fledged three, three fledged two and one fledged a singleton. The resulting productivity figure of 1.75 was the second lowest on record, 31.6% up on the record low of 2010 but 34.5% lower than the 2002-2011 mean (2.67±s.e.0.29). Ten young were colour ringed in 2011.

Sunday, February 13, 2011

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