Manx Shearwater – 2012

Puffinus puffinus – ADERYN-DRYCIN MANAW – Numerous breeding summer visitor. Recorded in all months

Hormones dictate when youngsters fly the nest

Published Thursday 5 July 2012

Image credit: David Boyle

Seabirds feed their young less as they reach an age to fly the nest, but it’s hormones that actually control when the chicks leave home, according to new research from the University of Leeds.

The study – published in Behavioural Ecology – aimed to pinpoint the main trigger which causes chicks to leave the nest and embark on an independent life, a process known as fledging.

While studying a colony of Manx Shearwaters (Puffinus puffinus), on the island of Skomer, researchers from the University’s Faculty of Biological Sciences noticed that parent birds seemed to become increasingly insensitive to their chicks’ demands for food as they grew close to fledging. At the same time the chicks showed a marked increase in levels of the hormone corticosterone. However, the team needed to know whether this increase was independent of, or caused by, the reduction in feeding.

They decided to trick the parent birds, by swapping chicks of different ages between nests – which the birds make in burrows in the ground – to see how this affected both parental care and the time chicks took to fledge.

“Manx Shearwaters don’t recognise their own offspring, but will simply go back to the same nest after they’ve gathered food. They have one chick, which makes the interactions between parent and offspring easier to study,” explains lead researcher, Dr Keith Hamer. “We swapped chicks which were between 10 days and two weeks apart in age, to see what impact it would have. We wanted to find out whether parents and chicks were responding to each other’s behaviour, or whether each was acting independently.”

The team discovered that adults reduced their food provisioning after about 60 days of raising a chick, regardless of the chick’s stage of development. Although females more than males will adjust their feeding levels to how much their chicks beg for food, after around 60 days both parents start to ignore their pleas. This held true whether parents were feeding their own chicks, or foster-chicks of different ages.

The surge in corticosterone took place over the final few weeks before chicks fledged at about 70 days of age. This held true even when chicks had been fostered by parents at a different stage of the feeding cycle, so was clearly independent of the parent’s behaviour and any reduction in food. 

“Our findings show that young Manx Shearwaters leave home of their own accord when their corticosterone levels have reached a peak rather than as a result of changes in parental behaviour,” says Dr Hamer. “Both parents and chicks need large energy reserves for their arduous migration across the Atlantic to South and Central America, and parents seem to reduce how much they feed their young simply to protect themselves.”

“Unlike some other bird species, which let their offspring dictate the level of care, seabirds appear to weigh up the cost of a chick fledging underweight against the greater cost of losing the chance to breed again,” he adds. “Manx Shearwaters have a breeding life of around forty years, so parents pay a high cost if they end the season too weak to complete their own migration.”

Press release by Univeristy of Leeds

Keith Hamer et alParent–offspring conflict during the transition to independence in a pelagic seabird.Behavioural Ecology, 2012 DOI: 10.1093/beheco/ars079

More about the Manx Shearwater in Pembrokeshire

Manx Shearwater – 2008

Puffinus puffinus – ADERYN-DRYCIN MANAW – Numerous breeding summer visitor. Recorded in all months

Migration and stopover in a small pelagic seabird, the Manx shearwater Puffinus puffinus: insights from machine learning.

Abstract

The migratory movements of seabirds (especially smaller species) remain poorly understood, despite their role as harvesters of marine ecosystems on a global scale and their potential as indicators of ocean health. Here we report a successful attempt, using miniature archival light loggers (geolocators), to elucidate the migratory behaviour of the Manx shearwater Puffinus puffinus, a small (400 g) Northern Hemisphere breeding procellariform that undertakes a trans-equatorial, trans-Atlantic migration. We provide details of over-wintering areas, of previously unobserved marine stopover behaviour, and the long-distance movements of females during their pre-laying exodus. Using salt-water immersion data from a subset of loggers, we introduce a method of behaviour classification based on Bayesian machine learning techniques. We used both supervised and unsupervised machine learning to classify each bird’s daily activity based on simple properties of the immersion data. We show that robust activity states emerge, characteristic of summer feeding, winter feeding and active migration. These can be used to classify probable behaviour throughout the annual cycle, highlighting the likely functional significance of stopovers as refuelling stages.

Full article here

Citation: Guilford, T., Meade, J., Willis, J., Phillips, R. A., Boyle, D., Roberts, S., Collett, M.,Freeman, R. and Perrins, C. M. (2009). Migration and stopover in a small pelagic seabird, the Manx shearwater Puffinus puffinus: insights from machine learning. Proc. R. Soc. Lond. B 276, 1215-1223

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Manx Shearwater – 2003-07 breeding

Puffinus puffinus – ADERYN-DRYCIN MANAW – Numerous breeding summer visitor. Recorded in all months

Comparison with previous atlas:

1984-882003-07
Breeding confirmed33
Breeding probable
Breeding possible
No of tetrads occupied3 (of 478)3 (of 490)
Percentage of tetrads0.6%0.6%

The Manx Shearwater colonies of the Pembrokeshire islands total around 50% of the world population, with around 120,000 pairs on Skomer, 45,000 pairs on Skokholm and 4,000 pairs on Ramsey. Because of the importance of this Shearwater (in European and indeed World terms) these island have been designated a Special Protection Area for them (under the EC Directive on the conservation of wild birds (79/409/EEC)

They are very difficult to census accurately and methods have changed over the years, from simple estimates based on counts of birds seen at night, estimates of burrow densities through capture/recapture methods derived from known numbers of ringed birds, through to the present day estimates based on counts of burrows and the responses of adult birds to tape recordings of their calls. Each method has been refined and compared but throughout there has been strong evidence of a continuing slow increase in the populations in the last fifty years, perhaps with an indication of a reverse of this in the early 2000’s.

On Ramsey Island the small population (perhaps 1,500 – 2,000 pairs) has risen rapidly since the Brown Rats were removed in 2000. In 2008 the population was estimated as 4,000 pairs.

Steve Sutcliffe.

Records extracted from the Pembrokeshire Bird Reports, which may contain more detail than shown here.

More about the Manx Shearwater in Pembrokeshire

Manx Shearwater – 1994

Puffinus puffinus – ADERYN-DRYCIN MANAW – Numerous breeding summer visitor. Recorded in all months

1984-88
Breeding confirmed3
Breeding probable
Breeding possible
No of tetrads occupied3 (of 478)
Percentage of tetrads0.6%

The Manx Shearwater figures as the emblem of the Dyfed Wildlife Trust, an appropriate choice since internationally important numbers of the bird breed on its island reserves of Skomer (estimated 95,000 pairs in 1971 and 165,000 pairs in 1989) and Skokholm (35,000 pairs estimated in 1973). Small colonies also occupy Middleholm and North Bishop. Large numbers probably bred on Ramsey prior to the invasion of the island by brown rats, which is estimated to have taken place in around 1800 (Saunders, 1986). However, by the end of the nineteenth century numbers had greatly reduced, and Mathew (1894) could only suggest that “a few may breed”. No definite breeding records on Ramsey have been traced for subsequent years until R. Pratt’s record of 200 pairs in 1975 and the RSPB estimate of 300-400 pairs in 1992. In the past, Manx Shearwaters also bred on Caldey and perhaps St Margaret’s Island (Mathew 1894).

Manx Shearwaters return to the breeding colonies in late February and depart from late August, some young not leaving until well into October. They visit the nesting burrows only at night, a stratagem which limits the effects of predation by gulls.

They use all the sea areas around the county for feeding, particularly the southern Celtic Deep, increasing numbers penetrating further northwards as the season progresses. Varying numbers also use the Bristol Channel, sometimes following fish shoals as far upstream as the Severn Bridge. Large processions can be seen passing our headlands each evening as they head for the island colonies, assembling in rafts on the water to the seaward side to await nightfall before moving ashore.

A few remain in local waters throughout the winter but the majority cross the Atlantic to winter off the coast of South America, where they are found mainly between latitiudes 20°S and 30°S until December. Return passage may be by way of the west African coast and certainly through the Bay of Biscay. Some first and second year birds summer off Newfoundland and Nova Scotia while others return to their natal colonies, and also visit colonies elsewhere in the Irish Sea and possibly Scotland. Extreme ringing recoveries include a Skokholm­bred bird that wandered as far as South Australia by the beginning of its second year, and an eight- year old in Norwegian waters during May.

Some fledglings wander inland when they leave the colonies, with onshore gales blowing many into the Cleddau Estuary and beyond, sometimes as far as eastern England. The gales also result in passages of thousands off Strumble Head. Many of these could have drifted downwind into the Irish Sea to beat back out to regain their ‘ground’ but it is highly likely that some could be Scottish birds passing southwards through the Irish Sea.

Donovan J.W. & Rees G.H, 1994, Birds of Pembrokeshire

SAUNDERS, DR 1986. The Nature of West Wales. Barracuda Books

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Manx Shearwater – 1949

Puffinus puffinus puffinus

Mathew called Skomer “the largest breeding-station . . .in the British Isles,” which may be correct.  He believed that a few might nest on Ramsey; the Modern Universal British Traveller, 1779, states that the “Harry-bird” (ie the Shearwater, see Oxford Dictionary 1901) breeds at Ramsey, and there is a good description of it nesting in holes there.  Mathew gives some evidence that they were possibly breeding on St Margaret’s Island in 1893, and perhaps also on Caldey; he seems not to have known of the Skokholm colony.  About 25,000 pairs breed on Skomer, and at least 10,000 pairs on Skokholm.  Visits the whole coast at night, from March to August, and often heard calling inland (eg Haverfordwest)

R.M.Lockley, G.C.S.Ingram, H.M.Salmon, 1949, The Birds of Pembrokeshire, The West Wales Field Society

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Manx Shearwater – 1894

MANX SHEARWATER, Puffinus Anglorum. — Local name “Cockle”. Resident.

The Manx Shearwater is, without doubt, the most interesting of our Pembrokeshire birds, from the fact that Skomer Island is the largest breeding-station, and may be considered the metropolis, of the species in the British Isles. The numbers there are almost incredible. And yet any visitor to Skomer in the day time, who left the island before night, would probably fail to see a solitary Shearwater, and if he was ignorant of the indications of their presence, might depart quite unaware of the vast bird population slumbering beneath his feet. For, during the day, the “Cockles” are all asleep in their burrows; some of these they have stolen from, and perhaps share with the rabbits, others they have excavated for themselves. Some of the burrows go straight in, but the greater number have various turns and twists, so that it is a tedious business, sometimes, to dig to and to reach the single white egg, which is almost the size of an ordinary hen’s egg. We have sometimes met small parties of these Shearwaters abroad on the sea during the day-time, and during the autumn we have seen the water covered by large flocks of them throughout the day, but certainly at the nesting season they are almost exclusively nocturnal, and do not come out from their holes to feed until quite late at night.

One beautiful summer’s night that we spent on Skomer, with Mr. Mortimer Propert, for the purpose of making acquaintance with the Shearwaters, we were greatly surprised at the late hour they emerged from their burrows. We went out several times after sunset to search for them, but all in vain, none had appeared. Several times we resumed our game at whist in Mr. Vaughan Davies’ hospitable house, before we went out and were successful in discovering that the birds were at last upon the move, and this was close upon eleven p.m. The birds were then flying in numbers over the ground to and fro about the height of our heads, almost brushing our faces as they flitted past. Their strange wailing cry resounded on all sides, and they kept up an unearthly chorus until the first streak of dawn.

We saw numbers come forth from holes at our feet, flapping with their wings for a yard or two along the ground before they were able to rise into the air, and it seemed as if it was necessary for them that the ground should slightly incline downwards, in order that they might gain a bite upon the air.

The old sheep-dog of the farm was with us, and amused herself by catching the Shearwaters one after another, and bringing them uninjured to our hands. Not wanting any, we would then toss them up into the air, and let them go, once or twice getting the benefit of a vomit of the greenish oil which the bird is able to discharge, either when frightened, or for the purpose of defence. We watched the birds for a long time in the calm and semi-twilight of the beautiful night, and it appeared as if they flew about the island for a long time before going out to sea, and that others were constantly coming in again from the water. There seemed, indeed, no diminution in the numbers flying over the island all through the night, for when we at last retired to bed, we still heard the same wailing cries, often close outside our bedroom window.

It was not until day dawned that the chorus gradually died away, and rising early, and going out to take a walk over the island, we detected but a single Shearwater sitting at the entrance of its burrow, into which it scuttled on our approach. Thrusting our arm inside, we found that it was a straight burrow, as, lying down, we were just able to touch the egg at its end, also the bird. Mr. Vaughan Davies informed us that one year he ploughed cartloads of the poor “Cockles” into the ground for manure, setting boys at night to knock them down with sticks, and to kill them, as they came out of their holes.

Numbers of Manx Shearwaters nest on the adjoining island of Skokholm, which is uninhabited, and is merely a summer run for sheep. A few may nest on Ramsey Island, and we have seen the birds in Ramsey Sound, but Mr. Mortimer Propert is not sure that they do. The Shearwaters are occasionally seen in flocks in Fishguard Bay.

We were for some time doubtful, and rather incredulous, as to any Shearwaters nesting on Caldy, which in our opinion seemed too tame an island for them, but after the evidence that we subjoin, it is without question that a few do so, or at least upon the connected island of St. Margaret’s. In the summer of 1857, Mr. E. W. H. Blagg, who was then staying at Tenby, informs us that several evenings he saw a large flock of Manx Shearwaters flying off Caldy Island, and believed that the birds nested there. Mr. Dix states, “numbers breed at Caldy Island,” but we had an idea that they had ceased to do so since he wrote this, a quarter of a century ago. On several occasions, when we ourselves have visited Tenby, on making inquiries, we failed to find anyone who could tell us if there were still Shearwaters upon Caldy; indeed, we were once expressly told that no such birds were known upon the island.

Writing to us upon this point, Mr. C. Jefferys, of Tenby, states: “The Manx Shearwater used to breed upon Caldy, and I think a few still do now in the fissures of the cliffs. I can give you more decided information about St. Margaret’s Island, which, as you know, is connected with Caldy by a reef of rocks, dry at low water. While on this island last May (1893) I frightened out of holes and fissures four or five Manx Shearwaters; they appeared to come from cracks about half-way down the cliffs, and may, or may not, have been nesting there; it certainly looks as if they were.” We believe, ourselves, that the “Cockles” only frequent and nest on islands where there is a sufficient quantity of soil upon the top for them to dig their burrows, and that they are for this reason absent from islands that are mere rock, but this would certainly not apply to Caldy, which is suitable to the birds in every respect, except that it is too much run over, and the birds may therefore have been frightened away from it.

M Mathew, 1894, The Birds of Pembrokeshire and its islands.

More about the Manx Shearwater in Pembrokeshire

Manx Shearwater

Puffinus puffinus – ADERYN-DRYCIN MANAW – Numerous breeding summer visitor.

Manx Shearwater – 2012

Puffinus puffinus – ADERYN-DRYCIN MANAW – Numerous breeding summer visitor. Recorded in all months Hormones dictate when youngsters fly the nest Published Thursday 5 July 2012 Seabirds feed their young less as they reach an age to fly the nest, but it’s hormones that actually control when the chicks leave home, according to new research […]

Manx Shearwater – 2008

Puffinus puffinus – ADERYN-DRYCIN MANAW – Numerous breeding summer visitor. Recorded in all months Migration and stopover in a small pelagic seabird, the Manx shearwater Puffinus puffinus: insights from machine learning. Abstract The migratory movements of seabirds (especially smaller species) remain poorly understood, despite their role as harvesters of marine ecosystems on a global scale and […]

Manx Shearwater – 2003-07 breeding

Puffinus puffinus – ADERYN-DRYCIN MANAW – Numerous breeding summer visitor. Recorded in all months Comparison with previous atlas: 1984-88 2003-07 Breeding confirmed 3 3 Breeding probable Breeding possible No of tetrads occupied 3 (of 478) 3 (of 490) Percentage of tetrads 0.6% 0.6% The Manx Shearwater colonies of the Pembrokeshire islands total around 50% of […]

Manx Shearwater – 1994

Puffinus puffinus – ADERYN-DRYCIN MANAW – Numerous breeding summer visitor. Recorded in all months 1984-88 Breeding confirmed 3 Breeding probable Breeding possible No of tetrads occupied 3 (of 478) Percentage of tetrads 0.6% The Manx Shearwater figures as the emblem of the Dyfed Wildlife Trust, an appropriate choice since internationally important numbers of the bird […]

Manx Shearwater – 1894

MANX SHEARWATER, Puffinus Anglorum. — Local name “Cockle”. Resident. The Manx Shearwater is, without doubt, the most interesting of our Pembrokeshire birds, from the fact that Skomer Island is the largest breeding-station, and may be considered the metropolis, of the species in the British Isles. The numbers there are almost incredible. And yet any visitor […]