Manx Shearwater Puffinus puffinus

Status;  International importance;  Population estimates;  Distribution;  Annual abundance/ productivity; Phenology/diet/survival

 

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Description

Manx Shearwater vignette

The following has been adapted from original text by Stephen F. Newton, Kate Thompson and P. Ian Mitchell in Seabird Populations of Britain and Ireland (with permission from A&C Black, London).

 

Manx shearwaters spend most of the year at sea returning to land only to breed. They nest in burrows and under boulders, and come ashore only under the hours of darkness in order to evade predators such as great skuas and great black-backed gulls. They breed exclusively on islands, usually free of rats Rattus sp. that depredate eggs, chicks and adults. Manx shearwaters were believed to have been exterminated from their eponymous colony on the Calf of Man by the introduction of rats from a wrecked ship in the late 18th Century. More recently rats and cats Felis catus were responsible for the extirpation of Manx shearwaters from Canna (Lochaber). Those few colonies that occur on islands with rats are generally small and limited in distribution. The exception is on Rum (Lochaber), where the largest single colony in the world coexists with rats, though there is evidence that deleterious impacts are occurring. Coexistence has been allowed by shearwaters nesting on the slopes of the island's mountains at altitudes of more than 450m - higher than rats normally occur, though milder winters in recent years may be increasing the habitable range of rats into the shearwaters' range. 

 

Most of the estimated world population of c.340,000–410,000 pairs of Manx shearwaters breed in Britain and Ireland. Of the UK population, 40% breed on Rum, and 50% in Pembrokeshire on the adjacent islands of Skomer, Skokholm and Middleholm (all Dyfed).

 


Conservation status

 

Manx shearwater is currently identified as a conservation priority in the following:

EC Birds Directive - migratory species

Amber listed in Birds of Conservation Concern 4 (2015 update)

(further information on Conservation Designations for UK Taxa)

Amber listed in Birds of Conservation Concern in Ireland 2014-2019 (2014 update)


International importance

 

UK Population % Biogeographic Population % World Population
299,700 AOS* N/a 79.9

 

* AOS = Apparently Occupied Sites

The UK population figure (rounded to the nearest hundred) was derived from data in Mitchell, P.I., Newton, S.F., Ratcliffe, N. and Dunn, T.E. (eds.) 2004. Seabird Populations of Britain and Ireland. Poyser, London. This was also the source of figures for the Biogeographic and World populations.

 


UK population estimates and change 1969-2002 (census data)

 

Manx shearwaters' nocturnal and subterranean habits have caused problems for surveyors in the past. Hence, Operation Seafarer and the SCR Census' estimates of 175,000-300,000 pairs and 250,000-300,000 pairs respectively were based solely on order of magnitude estimates and should not be compared to results obtained during Seabird 2000 which represent the first attempt to survey and quantify accurately the number of Manx shearwaters breeding in the UK. Surveyors used tape-playback which involved playing calls of Manx shearwaters to elicit a response from adults occupying burrows during the day. Unfortunately, not all adults present at a colony will respond to the taped calls, thus counts of responses will underestimate numbers and therefore have to be adjusted by a response rate measured at the colony. Some colonies were also surveyed by counting burrow entrances that had visible signs of use, though this method is difficult or impossible to use in colonies that are shared with other burrowers, i.e. rabbits and Atlantic puffins, or where burrow entrances are obscured, i.e. under boulders or in thick vegetation.

 

The main gaps in survey coverage in the UK were in the Northern Isles (where only relict populations remain), Bearasay (Western Isles), Eigg and Muck (Lochaber) and the Sanda Islands (Argyll and Bute). However, the combined population of all these islands is thought to be no more than 1,000 apparently occupied burrows.

 

 

Operation Seafarer

(1969-70)

Seabird Colony Register

(1985-88)

Seabird 2000

(1998-2002)

UK Population estimate (AOS)* N/a N/a 299,678
% change since previous census N/a N/a N/a

 

* AOS = Apparently Occupied Sites

For census results for individual countries and Ireland, the Channel Islands and the Isle of Man see under relevant sections below.

 


Distribution/abundance

 

The Seabird 2000 census provides the most comprehensive recent assessment of the distribution and abundance of breeding seabirds. Numbers of Manx shearwater found in different regions, and a map showing location and size of colonies, are provided in the Seabird 2000 Manx shearwater results page (PDF, 1.0 mb).

 

An interactive map is available on the NBN Gateway, where you can filter to display only the Seabird 2000 data.  For more recent, but less comprehensive, coverage view the distribution on the NBN with all available contributing datasets.

 

The locations sampled during the annual Seabird Monitoring Programme provide some information on distribution and are accessible via the Seabird Monitoring Programme online database.

 

Annual abundance and productivity by geographical area

 

With reference to the regional accounts below please note the following.

Breeding abundance: graphs of abundance index with 95% Confidence Levels (CLs) are only shown for a region where the trend produced has been deemed accurate (see methods of analysis). Where a trend was thought to be inaccurate, graphs of abundance at major colonies in a region may be shown instead, particularly if such colonies hold greater than 10% of the regional population, are monitored frequently and may thus help illustrate regional population fluctuations outwith national censuses. Occasionally, too few data have been collected regionally to produce either of these.

Productivity: graphs of productivity are only shown if analysis of breeding success data produced a significant result for regional and/or year effects (again see methods of analysis). If results were not significant, then a regional mean productivity value is given. However, on some occasions too few data are available from which to provide a meaningful average. Furthermore, for 11 species where the quality of monitoring data available was considered high, population viability analysis was undertaken at the UK level and the results of this are also reported.   

 



 

Breeding abundance

 

The first comprehensive estimates of population size of Manx shearwater were obtained during the Seabird 2000 Census, when 299,678 pairs were estimated. Over 90% of the UK population is found on the islands of Rum in Scotland and on Skomer and Skokholm in Wales. Due to the logistical difficulty in monitoring this nocturnal and burrow-nesting species, little information exists from which to derive population trends since Seabird 2000, although the colony on Skomer was re-surveyed in 2011. However, census methods used in 1998 and 2011 differed markedly, introducing an element of uncertainty in the results (see 'Wales' tab for details).

 

Productivity

 

Because of the logistical difficulties involved, both in visiting remote islands and in collecting data from a nocturnal burrow-nesting seabird, breeding success is monitored at only a few Manx shearwater colonies in the UK (three colonies in Wales, two in Scotland and one in Northern Ireland). Analysis has shown that there is no statistically significant annual variation in productivity within the sampled colonies, with Manx shearwaters fledging an average of 0.66 chicks per breeding pair per year between 1986 and 2015.

 

 

Population estimates and change 1969-2002 (census data)

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (AOS*) N/a N/a 126,545
% change since previous census    N/a N/a N/a

 

* AOS = Apparently Occupied Sites

 

Breeding Abundance

 

The first comprehensive estimates of population size of Manx shearwater in Scotland were obtained during the Seabird 2000 Census, when 126,545 pairs were estimated. The majority of these (approximately 120,000 pairs) were found on Rum with a further 4,803 pairs in the next largest concentration on the island group of St Kilda (Western Isles). The Treshnish Isles (Argyll and Bute, 1,283 pairs) was the only other colony holding over one thousand pairs. Due to the logistical difficulty in monitoring this nocturnal and burrow-nesting species, no information exists on the population trends at these large colonies since Seabird 2000.

 

Productivity

 

Productivity data are currently collected mostly from colonies on Rum with data in some years available from Canna and Sanday. Analysis showed no statistically significant variation in average productivity between 1986 and 2015, with approximately 0.69 chicks fledged per AOS per year. On Canna, one of the SMP key sites, only six potential chicks fledged from over 750 burrows1. It is not known what caused this low breeding success. There is some evidence that predation of nests/chicks by brown rats Rattus norvegicus on Rum may affect breeding success. For example, in 2007, 25 eggs and 10 chicks showing signs of rat predation were found in the study area. This problem has been the subject of ongoing investigation; in most years some signs of rat activity are recorded although rarely is this quantified.

 

 

Population estimates and change 1969-2002 (census data)

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (AOS*) N/a N/a 367
% change since previous census    N/a N/a N/a

 

* AOS = Apparently Occupied Sites

 

Breeding Abundance

 

Relatively few Manx shearwaters nest in England with 367 AOS estimated during Seabird 2000. Most of these were spread around the Isles of Scilly (201 AOS) with Lundy (Devon) holding the only other colony (166 AOS, though a later re-assessment of the Seabird 2000 data put this figure at 297 AOS)2. Recently, eradication of rats from Lundy has benefited Manx shearwaters; a whole-island survey in 2008 estimated 1,081 AOS2 and further survey work in 2013 found 3,451 AOS - almost ten times the English population found during Seabird 2000. A survey of the Isles of Scilly in 2015 found 439 AOS on the same islands counted in 2006, however an additional 84 AOS were found at five other locations3, an increase of 160% from Seabird 2000.

 

Productivity

 

No systematic data on the productivity of Manx shearwaters in England have been submitted to the SMP.

 

 

Population estimates and change 1969-2002 (census data)

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (AOS*) N/a N/a 168,133
% change since previous census    N/a N/a N/a

 

* AOS = Apparently Occupied Sites

 

Breeding Abundance

 

Together with Scotland, Wales holds over 90% of the UK population of Manx shearwaters. The first comprehensive estimates of the population size were obtained during the Seabird 2000 Census, when 101,800 pairs were estimated on Skomer, 46,200 pairs on Skokholm and a maximum of 16,183 pairs on Bardsey. Smaller colonies of 1,000-3,000 pairs were recorded on Middleholm and Ramsey (Dyfed). Until recently little information existed on potential population trends. However, a census was carried out in 2011 on Skomer where the population was estimated to be 316,070 AOS4. This figure is greatly in excess of the estimate made just 13 years earlier and would require an increase of approximately 9% per annum, a very high value for a bird with a low reproductive rate (c.0.65) and a long period of deferred maturity. Various reasons for the apparent increase (e.g. immigration, lowering of age of first breeding, estimation of response rate) were considered and thought unlikely. However, survey methods used in 1998 and 2011 differed markedly so it was concluded that the methods used in one (or both) of the surveys were sufficiently flawed to account for the difference, or part of it4.

 

Productivity

 

Manx shearwater Productivity Wales 2015

Figure 1:Trend in breeding productivity (no. of chicks fledged per pair) of Manx shearwater in Wales, 1986-2015. Based on SMP data; view the methods of analysis (PDF 158 kb).

 

Productivity data are currently collected mostly from colonies on Skomer (since 1991) and Bardsey (Gwynedd, since 1996), with the addition of data from Skokholm since 2013. Since 1995, mean productivity at colonies in Wales has been relatively high but variable. Detailed monitoring and reporting has been undertaken on Skomer and highlights some problems faced by the shearwaters breeding there. Very low productivity was recorded between 1992 and 1994; the reasons for this are largely unknown although very wet weather in May 1993 (the poorest breeding season to date) flooded many burrows on Skomer. A lack of food may have affected breeding success on Skomer in 2007 and 2008; annual comparison of chick growth and adult food provisioning behaviour found that birds bred later and chicks attained lower peak and fledging masses than in any previous recorded year dating back to 19655. These changes were accompanied by a reduction in parental attendance at the colony, which was probably the result of parents switching to a dual foraging strategy in 2007 and 2008. These events were linked to higher sea surface temperature in the preceding winter and to a reduction in prey quality, as indicated by the mean body mass of two-year-old herring5.

 

On Skomer in 2012, lack of food around hatching time was considered to have had the highest effect on productivity (0.55 fledged young per egg laid) although wet weather and the flooding of a small number of burrows may also have contributed. In 2013, productivity increased slightly (0.60) and in 2014 the highest productivity was recorded since 1998 (0.71). Breeding success in 2015 was 0.60. This is slightly lower than the five year average of 0.63 (2011-2015) and the 1995-2015 average of 0.62. It is also 0.11 lower than the 2014 productivity of 0.716. On Bardsey, flooding also reduced breeding success in some parts of the study area in 2012, although this was compensated for by high values of success in drier areas. A greater threat on Bardsey are carrion crows Corvus coronewhich exploited accessible nest chambers in several years between 2002 and 2007 at least; the number of eggs removed ranged from 80 (in 2002) to 'several' (in 2007). However, in 2013, predation by corvids was not thought to be significantly higher than in previous years. Instead, low success of 0.61 chicks per breeding pair (2004-2012 average 0.73+0.02) was possibly due to cold and generally poor weather throughout the spring. Low productivity was consistent across the differing habitats of the island; burrows in lowland banks and walls, mountain slopes and sea cliff turf areas all performed poorly. None of the study burrows contained abandoned eggs which would indicate failure at an early stage7. In 2014 and 2015, breeding success on Bardsey was at 0.70 and 0.66 chicks fledged per pair, respectively.

 

 

Population estimates and change 1969-2002 (census data)

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (AOS*) N/a N/a 4,633
% change since previous census    N/a N/a N/a

 

* AOS = Apparently Occupied Sites

 

Breeding Abundance

 

As for the other countries in the UK, the first comprehensive estimates of population size of Manx shearwater in Northern Ireland were obtained during the Seabird 2000 census. Only two colonies are known, both in the Copeland Islands (Co. Down); Big Copeland was estimated to hold 1,766 AOS with a further 2,867 AOS on nearby Lighthouse Island (total 4,633). Both islands have only been re-surveyed once since Seabird 2000, in 2007, when 1,406 AOS were recorded on Big Copeland and 3,444 AOS on Lighthouse Island (total 4,850) indicating numbers had changed little overall8. Changes at the respective islands between these two censuses (-20% on Big Island and +20% on Lighthouse) may be associated with logistical difficulties in surveying this nocturnal, burrow-nesting species.

 

Productivity

 

Breeding success data has been collected near annually on Lighthouse Island, one of the Copeland Islands, since 20078. On average 0.73 chicks were fledged per pair per year up to 2013 (no data were collected in 2014 and 2015).

 

 

Population estimates and change 1969-2002 (census data)

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (AOS*) N/a N/a 32,545
% change since previous census    N/a N/a N/a

 

* AOS = Apparently Occupied Sites

 

Breeding Abundance

 

During Seabird 2000, 32,545 pairs of Manx shearwater were recorded in the Republic of Ireland although several small colonies each probably holding a few hundred pairs were not surveyed. The main concentration of colonies was in the south-west on the offshore islands of County Kerry, several of which each held between 2,000-10,000 pairs. In County Galway, Cruagh held 3,286 pairs with small numbers on a couple of other islands. A few small colonies were recorded in counties Wexford and Dublin. Due to the logistical difficulty in monitoring this nocturnal and burrow-nesting species, no information exists as to population trends since Seabird 2000. 

 

Productivity

 

No systematic data on the productivity of Manx shearwaters in the Republic of Ireland have been submitted to the SMP. Thus, data is only available from Northern Ireland (see relevant section of report).

 

 

Population estimates and change 1969-2002 (census data)

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (AOS*) N/a N/a 37,178
% change since previous census    N/a N/a N/a

 

* AOS = Apparently Occupied Sites

 

Breeding Abundance

 

The first comprehensive estimates of population size of Manx shearwater for Ireland were obtained during the Seabird 2000 Census, when 37,178 pairs were estimated. The majority of these (approximately 33,000 pairs) were found in the Republic of Ireland where many colonies exist on offshore islands. In contrast, only two colonies are known in Northern Ireland, both in the Copeland Islands. During Seabird 2000, Big Copeland was estimated to hold 1,766 pairs with a further 2,867 pairs on nearby Lighthouse Island (total 4,633). A repeat census of these islands in 2007 recorded 1,406 pairs on Big Copeland and 3,444 pairs on Lighthouse Island (total 4,850) indicating numbers had changed little overall. Changes at the respective islands between these two censuses (-20% on Big Island and +20% on Lighthouse) may be associated with logistical difficulties in surveying this nocturnal, burrow-nesting species. For the same reason, no other information exists as to population trends for the whole of Ireland since Seabird 2000.

 

Productivity

 

No systematic data on the productivity of Manx shearwaters in the Republic of Ireland have been submitted to the SMP. Thus, data is only available from Northern Ireland where breeding success has been monitored near annually on Lighthouse Island, one of the Copeland Islands, since 20078. On average 0.73 chicks were fledged per pair per year up to 2013 (no data was collected in 2014 and 2015).

 

 

Population estimates and change 1969-2002 (census data)

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (AOS*) N/a N/a 34
% change since previous census    N/a N/a N/a

 

* AOS = Apparently Occupied Sites

 

Breeding Abundance

 

The population of Manx shearwaters on the Isle of Man is small and confined to the Calf of Man; during Seabird 2000 only 34 AOS were recorded. In 2005, tape playback methods obtained responses from 104 burrows and 91 burrows were found to be occupied in 2010. With the completion of a rat eradication programme on the Calf of Man in recent years the population has increased substantially; counts of apparently occupied burrows between 2011 and 2014 recorded 127, 147, 305 and 424 in each year respectively. No data have been provided to the SMP for 2015.

 

Productivity

 

No systematic data on the productivity of Manx shearwaters on the Isle of Man have been submitted to the SMP.

 

 

Population estimates and change 1969-2002 (census data)

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Seabird 2000    

(1998-2002)

Population estimate (AOS*) N/a N/a 10
% change since previous census    N/a N/a N/a

 

* AOS = Apparently Occupied Sites

 

Breeding Abundance

 

The known population of Manx shearwaters on the Channel Islands is small at only 10 AOS. These were split evenly between Jethou and Little Sark. There has been no assessment of the population since Seabird 2000

 

Productivity

 

No systematic data on the productivity of Manx shearwaters on the Channel Islands have been submitted to the SMP.

 

 


UK phenology, diet, survival rate

 

Phenology

 

No systematic data on phenology (timing of life-cycle events) have been collected as part of the SMP.

 

Diet

 

No data on diet have been collected as part of the SMP.

 

Survival rate

 

Figure 1 shows the survival rate of adult Manx shearwaters at Skomer, the only colony at which this parameter is monitored in the UK. Although adult breeding survival varied greatly since 1992, there is a clear decline since 2007 in breeding adult survival, which may be a potential concern for Manx Shearwaters on Skomer Island6.

The survival rate for adult breeding Manx Shearwaters at Skomer from 2013 to 2014 was 0.84, slightly below the study average (1978-2013: 0.86) As reported previously, these survival estimates remain low, both in comparison with more detailed studies carried out in the 1960s and 70s on Skokholm and with what might be expected for a bird with such a low reproductive rate. Survival has been particularly low recently for unknown reasons.

Manx shearwater adult survival rate

Figure 1: Estimated adult survival rate of Manx shearwaters on Skomer (Dyfed), 1986-2014.

 


References

 

1 Swann, R.L., Aiton, D.G., Call, A., Foster, S., Graham, A., Graham, K and Young, A. 2016. Canna seabird studies 2015. JNCC Report 474l, Peterborough.

2 Brown, A., Price, D., Slader, P., Booker, H., Lock, L. and Deveney, D. 2011. Seabirds on Lundy: their current status, recent history and prospects for the restoration of a once important bird area. British Birds 104: 139-158.

3 Heaney, V., and St Pierre, P. 2015. The status of seabirds breeding in the Isles of Scilly 2015. Isles of Scilly Seabird Recovery Project Report 2015.

4 Perrins, C.M., Wood, M.J., Garroway, C.J., Boyle, D., Oakes, N., Revera, R., Collins, P. and Taylor, C. 2012. A whole-island census of the Manx shearwaters Puffinus puffinus breeding on Skomer Island in 2011. Seabird 25: 1-13.

5 Riou, S., Gray, C.M., Brooke, M.d.L., Quillfeldt, P., Masello, J.F., Perrins, C. and Hamer, K.C. 2011. Recent impacts of anthropogenic climate change on a higher marine predator in western Britain. Marine Ecology Progress Series 422:105-112.

6 Stubbings, E.M., Büche, B.I., Miquel Riera, E., Green, R.M. & Wood, M.J. 2015. Seabird monitoring on Skomer Island in 2015. Unpublished Report to JNCC.

7 Bardsey Bird and Field Observatory. 2013. Annual breeding bird report 2013. Unpublished report; BBFO.

8 Northern Ireland Seabird Report 2015. 2016. Leonard, K. and Wolsey, S. (eds.). British Trust for Ornithology, Thetford.

 


Partners

Data have been provided to the SMP by the generous contributions of its partners, other organisations and volunteers throughout Britain and Ireland. Partners to the SMP are: BirdWatch Ireland; The British Trust for Ornithology; Centre for Ecology and Hydrology; Natural Resources Wales; Department of Environment, Food and Agriculture (Isle of Man); Department of Environment, Heritage and Local Government (Republic of Ireland); States of Guernsey Government; JNCC; Manx Birdlife; Manx National Heritage; The National Trust; National Trust for Scotland; Natural England; Northern Ireland Environment Agency; The Royal Society for the Protection of Birds; Scottish Natural Heritage; Seabird Group; Shetland Oil Terminal Environmental Advisory Group; Scottish Wildlife Trust.  More about the SMP partners >>

 
Image of Manx shearwater appears courtesy of Ian Rendall ©, is subject to international copyright law and may not be reproduced in any form whatsoever.