A summary of breeding seabirds on Skokholm in 2015. Total Productivity (2014 & 2013 in parenthesis) (2014 & 2013 in parenthesis) Fulmar 179 aia (179, 170) 0.47 (0.53, 0.34) Manx Shearwater 247 responses in 7000m2 (217, 214) 0.68 (0.63, 0.75) Storm Petrel 130 responses in transects (121, 129) 0.55 (0.69, -) Puffin 6665 adults (5070, 4834) 0.55 (0.50, 0.49) Razorbill 2382 aol (2052, 2294) 0.23 (0.39, 0.67) Guillemot 3603 aol (3512, 3466) - (-, 0.55-0.61) Lesser Black-backed Gull 1486 aia (1565, 1476) 0.15 (0.30, 0.16) Lesser Black-backed x Larus hybrid 1 nest (2, 2) 0 (0, -) Herring Gull 289 nests (300, 263) 0.66 (0.70, 0.72) Great Black-backed Gull 83 nests (84, 74) 1.66 (0.93, 1.80)

Cover: Storm Petrel over the Knoll © Bart Vercruysse over Knoll the © Vercruysse Petrel Bart Storm Cover: Fulmar Fulmarus glacialis Aderyn-drycin y Graig Fairly Common Breeder first bred in 1967 1936-1976: 34 trapped

Birds were present on ledges from the return of staff on 5th March. Colony attendance fluctuated during the remainder of the month, with all of the birds from different subcolonies departing on different days. There were high counts of 128 on the 19th, 115 on the 13th and 92 on the 27th, but on the 13th there were no birds in Peter’s Bay and on the 27th there were no birds around South Haven and only ten at North Gully. There were lows of 14 on the 12th, 34 on the 14th and 36 on the 31st when the majority of subcolonies were empty. The prevailing weather had a significant influence on colony attendance; during gale force northwesterlies on the morning of the 26th there were only three birds in North Gully, but as conditions ameliorated in the afternoon the count increased to 35. However good March weather does not always increase attendance; seas were calm and the wind a light southeasterly when the 34 birds were logged on the 14th. Birds were mating in Hog Bay on the 29th. April attendance was less sporadic, with 12 days of three figure counts (11 in 2014) and peaks of 134 on the 11th and 24th and of 163 on the 29th (the April 2014 high was 171 on the 27th). From the 6th onwards the only counts lower than 80 were 72 on the 17th, 54 on the 18th, 47 on the 26th and 71 on the 27th (all days with light winds). In May counts did not reach three figures until the 17th, with lows of 41 on the 5th, 36 on the 6th and 44 on the 8th all coinciding with gales. Numbers increased towards the end of May and the first egg was noted at North Gully on the 21st (the 28th in 2014).

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The three study plots counted annually since 2006 were visited on ten dates between the 4th and 14th June. The mean plot count between 2008 and 2014 has consistently been three or four pairs above the lowest single visit count (see table below). However this year, during a ten day period of fine and consistent weather, there were 26 apparently incubating adults recorded on three dates, 27 on four dates, 28 on one date and 29 on two dates. Although the difficulties in accurately identifying a sitting bird are still apparent, this was a tight spread compared with previous years. The mean number of apparently incubating adults was the same as logged in 2014 and the highest recorded since the plots were instigated in 2006. Although the total was the same as in 2014, there was one less pair at Little Bay Point (for a second consecutive year) but one more pair at Middle Rock (also for a second consecutive year).

The whole Island totals (apparently incubating adults), mean plot totals, range of totals over the ten study plot visits and the percentage of the Island total made up of study plot birds. 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Island 142 135 119 116 118 128 136 170 179 179 Plots 26 23 19 20 20 19 20 25 27 27 Range (16-25) (16-27) (17-24) (16-22) (16-25) (22-28) (23-29) (26-29) Plot % 18.3 17.0 16.0 17.2 17.0 14.8 14.7 14.7 15.1 15.1

The whole Island count of apparently incubating adults mirrored the study plot counts, with the plots again making up 15% of the Island total. The total of 179 pairs was the same as observed in 2014 and is the highest recorded on Skokholm, exceeding the previous peaks of 170 in 1997, 176 in 2002 and 170 in 2013. The 2015 whole Island count again includes approximately 40 pairs which would be difficult or impossible to see from the Island itself (birds north of North Gully, near Wreck Cove, on the Little Neck and in the hidden coves of Near Bay and Far Bay). The dip in numbers observed between 2006 and 2012 may perhaps be linked to a lack of boat access. It is possible that the increase in Fulmar numbers may affect other species; a heavily Fulmar-oiled Herring Gull was found on its South Haven nest on 30th May and four days later a Fulmar pair had occupied the nest site and the Herring Gull chicks lay dead.

The total number of apparently incubating Fulmar recorded on Skokholm since breeding began in 1967 and the number within the study plots since 2006. 180 160 140 120 100 80 60 40 20

0

1968 1988 1995 2015 1966 1967 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1989 1990 1991 1992 1993 1994 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 1965 On 1st June 47 incubating adults were selected for productivity monitoring (ten at Twinlet, six at North Gully, 20 around Little Bay Point and 11 at Peter’s Bay). Of these 15 failed at the egg/small chick stage, two failed having produced a chick (in both cases the chick was only seen once) and a further eight failed having reared a chick to 20 days or more (with one failure after a minimum of 20 days and further failures at a minimum of 26, 29, 34 (two), 39, 41 and 47 days). Although the cause of a failure was generally not apparent, a dead chick in Peter’s Bay decomposed in the nest (dead at

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34 days) whilst the remaining seven large chicks disappeared. Although the largest two chicks had reached an age where fledging has been noted at some sites, neither was sufficiently developed to fledge. Thus 22 (46.81%) of the monitored attempts produced a fledgling; a productivity estimate of 0.47 fledglings per pair is 11.3% down on the 0.53 logged in 2014 but 9.3% up on the post 1972 average of 0.43. The 2013 and 2014 figures were heavily influenced by poor productivity at Peter’s Bay; Peter’s Bay productivity in 2013 was 0.06 (compared with an overall figure of 0.34) and in 2014 it was 0.33 (compared with 0.53 overall). This year again saw productivity considerably lower than the Island as a whole, with a figure of 0.18 obtained from 11 monitored nests. The reason for this discrepancy is unclear.

Fulmar productivity (total number of fledged chicks per monitored pair) for each year that it has been calculated between 1972 and 2015. 0.70 0.60 0.50 0.40 0.30 0.20 0.10

0.00

1977 1984 1991 1998 2005 2012 1971 1972 1973 1974 1975 1976 1978 1979 1980 1981 1982 1983 1985 1986 1987 1988 1989 1990 1992 1993 1994 1995 1996 1997 1999 2000 2001 2002 2003 2004 2006 2007 2008 2009 2010 2011 2013 2014 2015

A tiny chick was found on 17th August, 48 days after the first chick sighting of the season; this attempt went on to fail. The first two fledglings could fly by 20th August (23rd August 2014 and 25th August 2013). The number of birds around the cliffs dropped rapidly as the fledglings departed, with no more than 49 noted in early September and only single figure counts from the 10th (when the last productivity sample chick departed), although census totals were bolstered by 17 off the Lighthouse on the 12th and 18 at sea on the 13th. The last bird left the cliffs on 20th September and up to six were seen at sea on four dates to the end of the month. Singles on the 7th and 21st October were the only records until the 23rd, from when 39 birds were logged over five dates until the 31st (with a high of 21 on the 25th); this was a similar absence to that noted in 2014 but contrasts with the higher counts

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logged in late October 2013 when numbers peaked at 155 on the 30th. In November there were 49 in Broad Sound on the 4th and 50 the following day included birds sheering the cliffs but not landing. There were then daily records from the 7th until the departure of staff on the 26th. A single landed on the cliffs on the 11th and up to 78 birds occupied ledges on six further dates. Peak counts were 105 on the 20th, 134 on the 23rd, 136 on the 24th and 124 on the 25th.

Manx Shearwater Puffinus puffinus Aderyn Drycin Manaw Very Abundant Breeder a 2012-2013 census estimated approximately 38000 pairs (46184 in 1998) 1499 trapped (including 119 pulli), 532 retrapped, 5 controls 1936-1976: 169,895 trapped, 2011-2014: 3864 trapped, 1533 retrapped, 7 controls

Four seen near the Lighthouse on 20th March were the first of the year, four days earlier than the first of 2014 but six days later than in 2013. A further 68 birds were logged before the end of the month including the first two birds heard calling diurnally from burrows on the 27th and the first to be seen at sea on the 28th. April counts were unusually low, with the only four figure count the 1380 logged from the Lighthouse on the evening of the 5th; this paucity of records was almost certainly influenced by the calm conditions prevalent during the period. A combination of weather and moon cycle again influenced the seawatch counts in May; the high of 22070 on the 6th came at the full moon but during a southwesterly gale, whilst the next highest count of 14440 on the 27th came during light winds but before a dark night. The 10000 birds logged on 10th June was the highest count of the month and, as in May, coincided with the full moon but near gale force winds from the southwest. This was a pattern which continued into July, with the peak count of 31700 on the 27th again coming close to the full moon but during a southwesterly gale. There were four further five figure counts during the month (on the 4th, 5th, 6th and 24th), all days with strong southwesterly winds. In August there were 22031 logged on the 2nd, 12290 on the 4th and 12000 on the 11th, the former two counts coinciding with gales and the latter with the new moon.

A Manx Shearwater study transect was established in 2013. It was defined as the track between the Observatory and the Lighthouse and the length of a landing net to either side; ringers were not to deviate from the track. The aim was to see whether, by ringing birds on the surface in this defined area, the retrap data could be interpreted to provide large sample size estimates of adult survival and the recruitment of juveniles to the breeding population. This is very much a project in its infancy and it is too early to draw any conclusions, but here follows a brief summary of the results so far. Of the 875 adult birds ringed along the transect in 2013, 182 (20.8%) were retrapped and an additional nine were found predated in 2014 (with two also predated in the year of ringing). A further 53 of the

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875 were retrapped this year (having not been retrapped in 2014), 31 were retrapped which had been handled in 2014 and a further five birds were found dead (one of which had been retrapped in 2014). Thus, of the 875 adults ringed in 2013, 250 (28.6%) have been encountered subsequently including 16 birds (1.8%) found predated by Great Black-backed Gulls. There were 331 fledglings ringed along the Lighthouse Track in 2013 and 11 were encountered this year as two year olds. Of the 1425 adult birds ringed in 2014, 163 (11.4%) were retrapped this year and a further 12 were found dead. The number of known age birds along the transect is increasing; along with the 331 fledglings ringed in 2013, there were 374 ringed in 2014 and 286 were ringed this year.

Three areas of study burrows, that is to say natural burrows where a paving slab covers a manmade access point to the nest chamber, were established in 2012 and 2013 with all birds encountered within the burrows ringed. Of 141 breeding adults bearing rings in 2013, 95 (67.4%) were found this year and 123 were definitely alive in 2014 (87.2%). Of 277 breeding adults bearing rings in 2014, 215 (77.6%) were found this year. These figures are not an accurate estimate of adult survival as there was no searching for marked birds in neighbouring, non-study burrows. It does however give a good indication of burrow fidelity and shows an interesting correlation with the stability of the colony; in the fragile Lighthouse colony 48 (58.5%) of marked birds were in the same burrow as in 2013, whereas in the more stable Crab Bay and Quarry Track colonies 34 (82.9%) and 14 (77.8%) were still present respectively. Of 37 breeding adults at Crab Bay in 2014, 34 (91.9%) were present in the same burrows again this year. The fragile nature of the Lighthouse colony, along with the high density of burrowing birds, sees the structure of the breeding tunnels change annually and clearly some lose their suitability as nest sites. Interestingly 28 (50.0%) of the 56 missing birds at the Lighthouse colony had failed with their breeding attempt in the previous season and two (66.7%) of the three missing birds at Crab Bay had also failed (the overall 2014 failure rate was 37.4%). This perhaps suggests that the missing birds may have opted for a more suitable nesting site rather than perished, although several other factors could be at play.

The study burrows also facilitate an accurate assessment of breeding success on Skokholm. Of 155 study burrows at the Lighthouse, 117 were occupied by a pair which produced an egg (118 in 2014). Of 12 study burrows along the track to the Quarry, eight pairs produced an egg (nine in 2014). Of 26 study burrows inland of Crab Bay, 23 pairs produced an egg (20 in 2014). There were thus 148 burrows this year from which productivity could be assessed. Of these 40 definitely failed at egg or very small chick stage (but dead chicks were not found). A further four pairs failed with a small chick and three pairs lost relatively large and healthy chicks which were probably predated. For a chick to be assumed to be of fledging size it was required to reach a wing length in excess of 190mm (although not necessarily ready to fledge, we have shown that chicks larger than this size may swap to a different burrow and thus go undetected). There were 101 chicks which reached this size in

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2015. Productivity was thus 0.68 fledging sized chicks per breeding pair (or 68.24% of pairs produced a fledging sized chick). This is a 7.9% increase on the 2014 figure of 0.63 (62.59% of pairs). It should be noted that this is the number of chicks which attained fledging size and does not reflect the number of fledglings which are lost to Great Black-backed Gull (and to a lesser extent corvid) predation as they exercise their flight muscles and make their first flights (see below). Having said that, only one of the fledglings ringed in the study plots was found predated.

A further 17 study burrows were opened this year at the westerly end of the South Coast Path. The inhabitants were the first Manx Shearwaters to be GPS tracked on Skokholm. This OxNav project, led by Oliver Padget and Professor Tim Guilford, was to investigate the feeding grounds used by Skokholm birds during chick feeding and compare them with those being used by Skomer birds during the same period. The comparative analysis of the data is ongoing, but here we include a track from a single bird exhibiting a similar feeding strategy to that previously described from Skomer. The bird made short trips to collect and deliver food for its chick before making a longer journey to a productive feeding ground where it could efficiently replenish its own energy reserves. The birds typically take their longer trips when their chick is being fed by their short-tripping partner (Padget, pers. comm.).

In 1999 nine study areas, each a circle of 1000 square metres, were established to allow a reasonable subset of the Skokholm Manx Shearwater population to be monitored from year to year. Two of these plots were discontinued, one in 2006 and one in 2007, as the survey work was disturbing the Lesser Black-backed Gull colonies. A new plot was established in 2006 to maintain a good sample area, however only seven plots have been sampled for a full 16 years. On each annual visit the number of burrows within the area is counted, along with the number of burrows from

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which a response is elicited when the call of a male bird is played down them. The standard correction factor (1.98) is then used to calculate the population within the area (see the 2013 and 2014 Seabird Reports for checking of the correction factor).

The total number of burrows, responses and the calculated population estimate for the 7000 square meters sampled annually since 1999. 1800 1689 Responses 1546 1600 Population 1408 1408 1442 1351 1338 1335 1346 Burrows 1400 1244 1226 1199 1159 1200 1056 1055 994 1000 816 798 800 661 602 527 539 507 600 457 453 489 444 412 403 426 434 442 424 429 334 400 266 272 304 224 231 256 229 215 219 223 214 217 247 200

0 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015

The crash from 2007 numbers was previously attributed to the collapse of many burrows in the more fragile areas of Skokholm, particularly near the Lighthouse which was at one time the densest area of breeding Manx Shearwaters on the Planet (Smith et al., 2001). Although this may certainly have played a role, it seems unlikely that this would be a major factor as there are considerably more burrows than pairs and the number of burrows appears to fluctuate independently of the number of tape playback responses. The eighth sample plot, begun in 2006, shows nicely the apparent lack of connectivity between the number of burrows and the apparent number of breeding pairs (see graph below). This may be attributable to the number of burrows frequently being altered by rabbits, the weather, in some areas by Puffins and perhaps most markedly in some places, the digging of non-breeding Manx Shearwaters, particularly later in the season.

The total number of burrows, responses and the calculated population estimate for the 1000 square meter plot sampled annually since 2006.

350 303 313 357 285 288 300 261 252 241 253 250 215 200 Responses 156 Population 150 113 97 Burrows 100 61 71 73 61 59 48 44 50 79 57 36 37 49 0 31 31 30 24 22 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015

Although the number of responses from the new plot (which lies to the south of North Pond) was the lowest since its introduction, the overall number of responses across 8000 square metres was the highest since 2008. This is the result of a small increase in the number of responses from six of

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the seven longer-term study areas, with a drop only noted at the plot in Gull Field to the north of the Hills. It would appear that the Skokholm breeding population can still be cautiously regarded as stable, although the observed variance in the percentage of birds which respond to the playback on a given day (see Brown and Eagle, 2013 and 2014) highlights both the degree of error in these numbers and the importance of continued monitoring. Some support for the theory that the population is stable comes from the study plots where the number of occupied burrows increased from 147 in 2014 to 148 this year (see above).

The estimated number of pairs in the 8000 square metres sampled since 2006. 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 869 954 620 525 499 495 501 521 477 533

In the period between 1957 and 1997 the number of dead Manx Shearwaters located on Skokholm was recorded in the daily census log. The corpses were either stored or thrown into the sea to ensure that the same birds were not counted more than once. The practice was stopped in 1997 as it was felt that the removal of the corpses would be impacting the specialist community of creatures evolved to exploit this food source. However, with a Great Black-backed Gull population more than twice the size it was when the counting was stopped, the study was begun again in 2014. To limit the impact on the scavenging community, the birds were left in situ but their wings were painted with stock marker so that they were not double counted. This year, in an effort to lessen the impact of the study still further, corpses were marked by neatly slicing the flight feathers of both wings. It was found that this could be readily achieved with a pair of kitchen scissors and that the mark was evident both at a distance and throughout the season.

As might be expected with a larger Great Black-backed Gull breeding population, the number of corpses located in 2014 was the most ever, although the average number of corpses per pair was lower than in all years except 1959, 1970 and 1971. One likely explanation was that the breeding gulls were disturbed between 1949 and 1985 which, although reducing the number of breeding pairs, probably inflated the non-breeding flock which would still be taking shearwaters. The number of Great Black-backed Gulls on Skokholm during the 2015 season was similar to 2014, both in terms of the breeding population and the non-breeding congregations. The number of corpses located was

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also similar, with 149 fewer marked overall this year (the result of finding 229 fewer adult corpses but 36 more young and 44 more puffinosised birds). Ringing recoveries during the first incarnation of Skokholm Bird Observatory suggested that the vast majority of the adult corpses are likely to be younger birds yet to reach breeding age (Brooke, 1990); however, with increased predation pressure from more Great Black-backed Gulls, it may prove that a higher percentage of breeding adults are being taken.

The number of Manx Shearwater corpses found between 1957 and 1983 from Gynn (1984) plus data from 1984 to 1991, 2014 and 2015. The number of Great Black-backed Gull breeding pairs is also included for each year. 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 Corpses 2465 1886 924 1354 1089 640 688 1059 857 946 GBBGU 27 30 30 10 12 5 7 12 8 10 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 Corpses 816 841 829 304 606 1350 1082 869 1051 1266 GBBGU 10 3 14 11 16 12 12 7 7 7 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 Corpses 1913 1820 1153 1024 1080 1479 1373 1316 1571 1068 GBBGU 6 10 10 10 11 16 11 14 11 10 1987 1988 1989 1990 1991 2014 2015 Corpses 1759 1760 1694 1915 2703 4272 4123 GBBGU 11 12 15 16 20 84 83

The number of Manx Shearwater corpses found during each week from 25th March until 3rd November 2015. 400 Puffinosis 350 Fledglings 300 Chicks 250 Adults 200

150

100

50

0

1/4-7/4 3/6-9/6 1/7-7/7 2/9-8/9

8/7-14/7 8/4-14/4 29/4-5/5 6/5-12/5 27/5-2/6 29/7-4/8 5/8-11/8 26/8-1/9 9/9-15/9

25/3-31/3 15/4-21/4 22/4-28/4 13/5-19/5 20/5-26/5 10/6-16/6 17/6-23/6 24/6-30/6 15/7-21/7 22/7-28/7 12/8-18/8 19/8-25/8 16/9-22/9 23/9-29/9 30/9-6/10

7/10-13/10 28/10-3/11

14/10-20/10 21/10-27/10 This is the beginning of what we hope will become a long-term study and it is too early to read much into the results. It is nevertheless worth noting that the decline in the number of predated adults observed in 2015 (from 2931 last year to 2702) came during a year when the rabbit counts from North Plain were nearly twice that observed in 2014. However, despite the increase in the rabbit population, the number of this year’s young found predated was very similar to last year (1324 in 2015 and 1288 in 2014). The dietary preferences of the gulls certainly warrant further study. Four of the adult Manx Shearwater corpses found during the survey were intact, perhaps the result of disturbance following the kill. These were dissected at the Observatory to investigate the contents of

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the digestive system; in all four cases there were no visible plastics. Interestingly there was a considerable increase in the number of dead showing signs of puffinosis this year (97 compared with 53 in 2014). Puffinosis is still a mysterious affliction which, possibly due to the actions of a virus which leads to bacterial infection, sees the development of blistered feet, conjunctivitis and problems with limb control; it is often fatal. The condition is usually considered to be prevalent in wetter areas and it is thus tempting to think that the observed increase may be due to the considerably higher rainfall experienced in 2015.

In an attempt to achieve a better understanding of how puffinosised birds are distributed across Skokholm during the course of the autumn, Dr. Matt Wood designed a transect route which was walked by Island staff over eight nights during September. The route led along Little Bay Wall and back, around to the Neck via Orchid Bog, returned to the Observatory buildings and headed in either direction along the Knoll Wall, looped through East Bog and ended at the Lighthouse via the main track. Each encountered fledgling was counted and inspected for signs of puffinosis, namely blisters on their feet, a loss of coordination, a fine shaking of their head or wings and conjunctivitis. The work will form part of a project led by Professor Pat Nuttall at the University of Oxford.

The number of Manx Shearwater encountered along the transect, the number which showed signs of puffinosis and the percentage of encountered birds made up of those showing signs. 1st-2nd 4th-5th 7th-8th 10th-11th 13th-14th 16th-17th 19th-20th 21st-22nd Birds 54 164 219 155 162 101 58 41 Puffinosised 3 29 63 31 55 55 32 10 % Puffinosised 5.6 17.7 28.7 20.0 40.0 54.5 55.2 24.4

The first fledglings were seen on the surface on 21st August, four days earlier than the first of 2014 and two days earlier than in 2013. Fledglings were first seen at sea on the 25th and two were eaten at sea by Great Black-backed Gulls on the same date. The number of birds littering the track to the Lighthouse each night was soon in three figures. The first fledgling affected by puffinosis was encountered on 27th August, one week earlier than in 2014. Over the course of the September puffinosis study, there were up to 63 affected individuals found on a single night. As the study progressed there was an upwards trend in the percentage of encountered birds exhibiting symptoms, perhaps not just a reflection of the emergence period of infected birds, but also an indication of their inability to fledge and thus their prolonged presence in the study area.

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The last adult bird to be encountered along the study transect was ringed on 5th September and a freshly dead adult was noted on the 10th. September seawatch counts peaked at 620 individuals on the 1st and 645 on the 11th with five further three figure counts logged between those dates. However there were only nine birds seen at sea on the 12th and there were no at sea records on the 16th, as in 2014 the first autumn day with no birds logged. Birds were noted at sea on only six further dates during the month, although fledglings were still encountered each night. In October there were five at sea on the 5th and singles on the 21st and 26th. On land birds were recorded each night until the 8th and a puffinosised bird was at the Well on the 11th and 12th. Other than a lone fledgling on the Lighthouse Track on the night of the 23rd, the only sign of a continued presence was the appearance of 12 freshly predated birds over five dates to the 24th. There followed the surprise reappearance of calling birds, with up to 11 individuals logged on a nightly basis during wet and misty weather between 31st October and 5th November. Two were at sea off the Lighthouse on the morning of 9th November, one was in Broad Sound the following day and a single in Broad Sound on the 17th was the last of the year, three days later than the last of 2014.

Ringing recovery EL87943 Originally ringed as an adult, CALF OF MAN, ISLE OF MAN 13th July 2015 Recovered HOME MEADOW, SKOKHOLM 18th July 2015 Finding condition At colony but not necessarily breeding Distance travelled 263km at 187 degrees (S) Days since ringed 5 An interesting recovery of what is perhaps a nonbreeding individual visiting different colonies.

Ringing recovery EY41558 Originally ringed as an adult, LIGHTHOUSE TRACK, SKOKHOLM 10th April 2013 Previously recovered as an adult, LIGHTHOUSE TRACK, SKOKHOLM 1st May 2014 Recovered CIDREIRA, RIO GRANDE DO SUL, BRAZIL 16th September 2014 Finding condition Freshly dead on beach Distance travelled 10116km at 206 degrees (SSW) Days since ringed 524

Ringing recovery EY96988 Originally ringed as an adult, LIGHTHOUSE TRACK, SKOKHOLM 21st April 2015 Recovered FLORIANOPOLIS, SANTA CATARINA, BRAZIL 8th November 2015 Finding condition Freshly dead on beach

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Distance travelled 9787km at 206 degrees (SSW) Days since ringed 201 Although the winter movements of Manx Shearwaters have now been closely tracked, winter mortality and its causes are less well understood. Prolonged south Atlantic storms this winter, the product of a particularly strong El Niño, are already being linked to increased shearwater mortality.

Ringing recovery EY96779 Originally ringed as an adult, LIGHTHOUSE TRACK, SKOKHOLM 16th June 2015 Recovered KIDWELLY, CARMARTHENSHIRE 23rd July 2015 Finding condition Dead on beach Distance travelled 66km at 87 degrees (E) Days since ringed 37

Ringing recovery FC86623 Originally ringed as a chick, SKOMER, PEMBROKESHIRE 9th September 1994 Recovered LIGHTHOUSE TRACK, SKOKHOLM 3rd May 2015 Finding condition Predated Distance travelled 4km at 163 degrees (SSE) Days since ringed 7541

Ringing recovery FC91022 Originally ringed as an adult, BARDSEY ISLAND, GWYNEDD 25th April 1997 Recovered RAT BAY, SKOKHOLM 3rd August 2015 Finding condition Predated Distance travelled 122km at 196 degrees (SSW) Days since ringed 6674

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Ringing recovery FP52758 Originally ringed as a chick, SKOMER, PEMBROKESHIRE 20th August 2003 Recovered HOME MEADOW, SKOKHOLM 2nd September 2015 Finding condition Predated Distance travelled 4km at 163 degrees (SSE) Days since ringed 4396 The above three recoveries show that it is not just the inexperienced non-breeders which fall prey to the Great Black-backed Gulls.

Ringing recovery FR48752 Originally ringed as a chick, SKOMER, PEMBROKESHIRE 15th September 1983 Recovered LIGHTHOUSE TRACK, SKOKHOLM 21st July 2014 Finding condition At colony but not necessarily breeding Distance travelled 4km at 163 degrees (SSE) Days since ringed 11267 There are still some birds over 30 avoiding the gulls.

Storm Petrel Hydrobates pelagicus Pedryn Drycin Abundant to Very Abundant Breeder 838 trapped (including 17 pulli), 85 retrapped, 33 controls 1936-1976: 18,526 trapped, 2011-2014: 1000 trapped, 51 retrapped, 39 controls

Despite the sizable breeding population on Skokholm, Storm Petrels again proved an exceptionally rare sight at sea with the only record a single heading west off the Light at 1700hrs on 25th August; all other observations came at night with the exception of a small number of incubating adults visible in shallow crevices and diurnal visits to nest boxes. A minimum of 30 birds watched at the Quarry on 22nd April was the first record of the year, two days earlier than the first of 2014. The first diurnal record was a vocal bird in the Cottage Garden Wall on 25th April. Nights in May saw small numbers observed at various locations around the Island and there were minimum counts from the Quarry of 100 on the 16th and 90 on the 26th. Although counting individuals at night gives a very poor indication as to colony size, using an infrared viewer to unobtrusively watch the behaviour of the birds is an unforgettable experience for our guests. Four study transects established at the Quarry in 2010, along with further plots in North Haven Gully and along two of the walls which radiate from the Farm, provide much more reliable population monitoring than nocturnal count data.

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For a second consecutive year we welcomed a long-term Storm Petrel volunteer who made ten visits to the study transects between 8th June and 15th July. A recording of male song was again played into every crevice encountered along the transects, both numbered (and therefore used previously) and unmarked, with each crevice from which a response was elicited being recorded and marked if new. It was first noted in 2013 how some study burrows had deviated from the two metre wide transects and in 2014 the data collected since 2010 was reassessed to bring it back in line with the original protocol. As was the case in 2014, the playback census this year was focused on the area of the transects delineated by marked burrows, although the results were then divided into those which fell within the true transect and those which fell just outside (see table below).

The total number of apparently occupied crevices (located over multiple visits) responding to a recording of male song at each of the seven study sites. Numbers in parenthesis are the totals from the 2m wide Quarry transects (as stipulated in the project guidelines) as opposed to the more wayward crevices included since the project’s inception. Year North Little North Quarry Quarry Quarry Quarry Quarry Total Pond Bay Haven transect transect transect transect total Wall Wall Gully 1 2 3 4 2010 4 9 18 8 (5) 15 (12) 11 (8) 32 (17) 66 (42) 97 (73) 2011 7 6 19 11 (5) 13 (8) 10 (7) 25 (14) 59 (34) 91 (66) 2012 5 9 21 12 (5) 8 (4) 10 (5) 33 (17) 63 (31) 98 (66) 2013 7 15 22 14 (4) 15 (8) 10 (7) 46 (27) 85 (46) 129 (90) 2014 9 12 13 14 (6) 18 (9) 18 (12) 37 (22) 87 (49) 121 (83) 2015 7 17 19 13 (5) 22 (9) 12 (7) 40 (23) 87 (44) 130 (87)

The total number of active crevices located this year was the highest of any during the six year project, however the increase was only slight and the population is best considered stable. This is positive news following the significant decline recorded between 1996 and 2010 (Sutcliffe and Vaughan, 2011).

A closer examination of the results reveals some interesting changes in the distribution of responding pairs. Although the number of responses from North Pond Wall has remained relatively constant during the study, this year saw a 41.7% increase in the number of responses from Little Bay Wall, a somewhat surprising result as it has been suggested that the degradation of the herringbone walls across the Island is reducing nest site availability. The increase could be due to the absence of two pairs of Great Black-backed Gull which nested along the wall in 2014; this species is known to predate Storm Petrels and their relocation this year could have allowed access to crevices previously too close to the predator’s nests. The increase observed at North Haven Gully will be in part due to improved access this year (access was curtailed in 2014 due to the instability of overhead rocks after the winter storms, a situation which remedied itself during last winter). However the increase may also reflect the return of pairs to new sites following the significant scouring event of winter 2013- 2014 which removed 21 traditional crevices, 16 of which had been used in 2013. Although there was little change in the number of responses from three of the Quarry transects, there was a 33.3% drop along transect three. This was a surprising result as this transect is remarkably stable, with little rock movement and crevices which remain open from year to year. This could perhaps indicate that some Storm Petrels, much like other Procellariforms, do not breed every year, but it may also reflect local losses to predation or winter mortality. Clearly there is an inevitable transience to the availability of Storm Petrel nest crevices, but there also seems to be evidence here that the birds can react to the changing landscape and maintain a stable population; this of course assumes that further nest sites open up as others are lost. Stable sites are also in existence; over a third of the active crevices located during this six year study have shown signs of occupancy in four or more years and over 13% of crevices have contained a calling bird in every year. It should be noted that the higher proportion

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of short term crevice occupancy highlighted in the below table will in part be explained by the discovery of a greater number of active crevices in recent years.

The number of crevices which have at some point been occupied over the six year study (a total of 221), subdivided to show how many years the crevices have been apparently occupied for and the percentage of crevices occupied for a particular number of years. Quarry The North Haven % of total Transects Walls Gully crevices 1 year of apparent occupancy 25 23 11 26.70 2 years of apparent occupancy 23 8 14 20.36 3 years of apparent occupancy 23 5 3 14.03 4 years of apparent occupancy 18 9 11 17.19 5 years of apparent occupancy 17 2 0 8.60 6 years of apparent occupancy 25 1 3 13.12 Total 131 48 42

Interestingly the occupied crevices along the study walls were clustered, despite the presence of seemingly suitable crevices elsewhere. This was also observed in North Haven where, of ten very similar nest boxes, the four which were occupied were adjacent to one another. These observations perhaps suggest that Storm Petrels prefer colonial nesting, something which will be worth taking into account if further artificial sites are to be made on Skokholm.

The percentage of known active crevices which responded to a recording of male song during any single visit was fractionally down on the previous two years, 5.0% down on 2014 and 3.2% down on the six year mean of 32.27%. Although there is some variance in this response rate between sites and between sampling seasons, it is possible to calculate a correction factor capable of predicting the number of active crevices within an area based on a single visit (as has become a standard monitoring tool for Manx Shearwater). If the six year mean response rate of 32.27% is used, then a correction factor of 3.09 would be most suitable for predicting the number of active crevices. This may be of some use at sites where access arrangements or time constraints limit the number of visits during the study period. It is unclear why the response rate for this species is so much lower than for Manx Shearwater, but it would seem likely that this is due to either male Storm Petrels being less inclined to respond than male Manx Shearwaters or perhaps due to the males spending less time incubating.

The percentage of known active crevices which responded to male song during any single visit, averaged across all visits. Year North Quarry Quarry Quarry Quarry Average Haven Gully transect 1 transect 2 transect 3 transect 4 2010 - 37.50 22.20 37.80 35.50 33.25 2011 35.56 33.64 17.69 24.00 33.20 28.82 2012 27.62 36.67 38.75 23.00 26.36 30.48 2013 39.55 36.61 38.33 33.75 36.69 36.99 2014 40.00 30.36 28.57 30.00 35.42 32.87 2015 37.37 31.54 32.73 28.33 26.19 31.23

In 2013 the thermal imaging camera recorded a Short-eared Owl hunting Storm Petrels in the Quarry, an event which is perhaps more regular than previously realised. This year there were 18 predated Strom Petrels located (16 in 2014), all but one of which were thought to have fallen prey to Short-eared Owls (either due to the presence of owl feathers or pellets). Short-eared Owls were recorded during every month of the 2015 season bar May, with the majority of spring and summer

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records coming from within or near the Quarry (where the majority of Storm Petrel corpses were found). However there is still no indication that there is a breeding population of owls on Skokholm, an absence typically associated with the lack of voles; that owls are commuting from the breeding population on Skomer seems likely. The majority of Storm Petrel corpses were adult birds, although a fledgling ringed at the Quarry was found in a pellet at Walls End. One corpse was found with the wings still attached to the sternum, as is typically the case with a gull kill (as seen with the Manx Shearwaters). Following an 18 year absence, a Little Owl was present around the buildings during the early spring of last year; it is pleasing to report that there have been no subsequent records.

There were 20 sites discovered this season where an incubating bird was evident early enough in the nesting period to allow a productivity estimate to be made (13 sites in 2014); although some early egg stage failures may have been missed, the study is biased towards birds in shallow crevices or boxes and the sample size is far from great, these visible birds provide a rare opportunity to estimate productivity. Two in natural sites and two in nest boxes failed at egg stage, two in natural sites and three in boxes failed at chick stage and six in natural sites and five in boxes fledged. Productivity was thus calculated at 0.55 fledglings per pair, a 20.3% drop on the 0.69 observed in 2014. There are several plausible explanations for this decline, perhaps the most influential being the more extreme weather experienced this year; on three occasions chicks were found dead after particularly violent rainstorms. As some of the 2015 study sites were not occupied in 2014 it is possible that the lower productivity seen this year could be attributed to the failure of first time breeders, less experienced birds which are more likely to fail. Another possible reason for the lower productivity estimate is that the sample size was slightly larger this year and thus perhaps more representative of the population as a whole.

The Storm Petrel breeding season is a protracted one; hatched eggshell found on 2nd July was the first indication of a chick this year, whilst an egg in North Haven did not hatch until 23rd September (although the chick later died). The growth of five nest box chicks was monitored from when they were known to be unattended during the day (see graph below). As in 2014, chicks in the more complex nesting areas, typically in rock fall rather than walls, were found to wander away from the natal cavity. This year these movements were recorded when the chicks were still small, the stimulus in at least one case being the weather; when its original nest filled with water, chick A7 moved to an adjacent cavity when its wing was less than 40mm. The periods of intense rainfall experienced this

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year were perhaps also responsible for a behaviour not witnessed in the previous two seasons. An adult in box A4 returned to brood its chick throughout the day on 23rd August when the chick had previously been left alone diurnally for 11 days. During the preceding visit the chick was found to be cold, damp and its weight gain had been slower than the other four monitored chicks (see graph below). Whether this was the reason for the return of an incubator or not, the chick went on to survive to fledging size whilst an adjacent unbrooded chick perished during the rainstorm. The weather very much affects chick development; the monitored chicks all exhibited weight loss during rough weather in late August and early September, although whether this was due to conditions within the nest chamber or conditions at sea affecting chick provisioning was not clear. All five chicks attained a weight of at least 40g, more than 25% heavier than most adults, with the heaviest in Little Bay Wall reaching 43.7g (2.8g down on the heaviest weight recorded during the more clement 2014 season).

Monitoring the development of five Storm Petrel chicks. Site A is the artificial wall above the Quarry, site LBW is Little Bay Wall (LBW 32 is the only site where the chick has been monitored for three successive years) and N is North Haven. 140 45

40 120

35 100

30

80 25 A4 wing A7 wing 60 20 Weight (g)

LBW 32 wing Winglength (mm) LBW 24 wing 15 N8 wing 40 A4 weight A7 weight 10 LBW 32 weight 20 LBW 24 weight 5 N8 weight

0 0

05-Sep 21-Sep 01-Sep 03-Sep 07-Sep 09-Sep 11-Sep 13-Sep 15-Sep 17-Sep 19-Sep

20-Aug 06-Aug 08-Aug 10-Aug 12-Aug 14-Aug 16-Aug 18-Aug 22-Aug 24-Aug 26-Aug 28-Aug 30-Aug

Adult Storm Petrels were mist netted on 11 nights this year, one more than in 2014. The largest catch was the 224 trapped on the night of 22nd July. Of all the birds handled this year, 12.3% (or nearly one in eight) was already wearing a ring (7.5% in 2014), there were five retraps from 2013, 22 retraps from 2014 and 33 (3.5%) of handled birds had been ringed elsewhere. Along with generating some fantastic data, these nights also proved very popular with guests to the Island. Unless stated otherwise, all of the following recoveries were of birds deliberately mist netted. Additional to the birds listed below, we received news of 21 birds ringed at Wooltack Point (4km to the NNE) retrapped on Skokholm (19 after 13 to 41 days, one after 362 and one after 379), two birds ringed on Skokholm retrapped on Wooltack (after 337 and 341 days), two birds ringed on Skomer (4km to

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the NNW) and retrapped on Skokholm (after nine and 356 days) and nine birds ringed on Skokholm and retrapped on Skomer (seven after one to 29 days, one after 351 and one after 373).

Ringing recovery 2591800 Originally ringed as an adult, CALF OF MAN, ISLE OF MAN 13th July 2015 Recovered SOUTH HAVEN, SKOKHOLM 16th July 2015 Distance travelled 263km at 187 degrees (S) Days since ringed 3

Ringing recovery 2591935 Originally ringed as an adult, CALF OF MAN, ISLE OF MAN 16th July 2015 Recovered SOUTH HAVEN, SKOKHOLM 30th July 2015 Distance travelled 263km at 187 degrees (S) Days since ringed 14

Storm Petrel ringing recoveries (over 10km) received since the Bird Observatory was reaccredited.

One bird from Skokholm One bird to Skokholm Two birds to Skokholm

Three birds to Skokholm

Four birds to Skokholm

Five birds to Skokholm

13 birds to Skokholm

Google Imagery © 2014 TerraMetrics

Ringing recovery 2661164 Originally ringed as an adult, EYEMOUTH, SCOTTISH BORDERS 6th August 2014 Recovered SOUTH HAVEN, SKOKHOLM 1st August 2015 Distance travelled 508km at 205 degrees (SSW) Days since ringed 360

Ringing recovery 2683192 Originally ringed as an adult, THE LIZARD, CORNWALL 7th August 2013 Recovered SOUTH HAVEN, SKOKHOLM 23rd July 2015

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Distance travelled 193km at 359 degrees (N) Days since ringed 715

Ringing recovery 2683307 Originally ringed as an adult, THE LIZARD, CORNWALL 16th June 2015 Recovered SOUTH HAVEN, SKOKHOLM 23rd July 2015 Distance travelled 193km at 359 degrees (N) Days since ringed 37

Ringing recovery 2683366 Originally ringed as an adult, THE LIZARD, CORNWALL 17th June 2015 Recovered SOUTH HAVEN, SKOKHOLM 16th July 2015 Subsequently recovered MWNT, CEREDIGION 26th July 2015 Distance travelled 193km at 359 degrees (N) (to SKOKHOLM) Days since ringed 29 (to SKOKHOLM)

Ringing recovery 2683444 Originally ringed as an adult, THE LIZARD, CORNWALL 16th July 2015 Recovered SOUTH HAVEN, SKOKHOLM 12th August 2015 Distance travelled 193km at 359 degrees (N) Days since ringed 27

Ringing recovery 2685804 Originally ringed as an adult, SOUTH HAVEN, SKOKHOLM 26th July 2014 Recovered CALF OF MAN, ISLE OF MAN 15th July 2015 Distance travelled 263km at 7 degrees (N) Days since ringed 354

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Ringing recovery 2685838 Originally ringed as an adult, SOUTH HAVEN, SKOKHOLM 29th July 2014 Recovered BARDSEY ISLAND, GWYNEDD 16th June 2015 Distance travelled 122km at 16 degrees (NNE) Days since ringed 322

Ringing recovery 2685875 Originally ringed as an adult, SOUTH HAVEN, SKOKHOLM 30th July 2014 Recovered ABERDOVEY, GWYNEDD 31st July 2015 Finding condition Dead on beach Distance travelled 124km at 42 degrees (NE) Days since ringed 366

Ringing recovery 2689155 Originally ringed as an adult, ANNAGH HEAD, MAYO, IRELAND 18th July 2014 Recovered SOUTH HAVEN, SKOKHOLM 11th August 2015 Distance travelled 429km at 132 degrees (SE) Days since ringed 389

Ringing recovery 2705168 Originally ringed as an adult, SOUTH HAVEN, SKOKHOLM 16th July 2015 Recovered GRASSHOLM, PEMBROKESHIRE 7th August 2015 Distance travelled 15km at 286 degrees (WNW) Days since ringed 22 There were three further birds ringed on Skokholm and retrapped on Grassholm, one of which was netted 16 days after ringing and two seven days after ringing.

Ringing recovery 2705774 Originally ringed as an adult, SOUTH HAVEN, SKOKHOLM 6th August 2015 Recovered PORTH YSGADEN, GWYNEDD 25th August 2015 Distance travelled 140km at 18 degrees (NNE) Days since ringed 19

Ringing recovery 2715077 Originally ringed as an adult, SOUTER LIGHTHOUSE, TYNE AND WEAR 19th July 2015 Recovered SOUTH HAVEN, SKOKHOLM 6th August 2015 Distance travelled 445km at 216 degrees (SW) Days since ringed 18

Ringing recovery SE23237 Originally ringed as an adult, BANNEG, LE CONQUET, FINISTÈRE, FRANCE 11th July 2013 Recovered SOUTH HAVEN, SKOKHOLM 23rd July 2014 Distance travelled 366km at 357 degrees (N) Days since ringed 377

Ringing recovery SE23331 Originally ringed as an adult, BANNEG, LE CONQUET, FINISTÈRE, FRANCE 12th July 2013 Recovered SOUTH HAVEN, SKOKHOLM 20th July 2014 Distance travelled 366km at 357 degrees (N) Days since ringed 373

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Ringing recovery SE25680 Originally ringed as an adult, BANNEG, LE CONQUET, FINISTÈRE, FRANCE 19th August 2014 Recovered SOUTH HAVEN, SKOKHOLM 22nd August 2014 Distance travelled 366km at 357 degrees (N) Days since ringed 3 Banneg is an island in the Molène Archipelago where fewer than 1000 pairs of Storm Petrel are thought to nest, the majority in abandoned Rabbit burrows.

Puffin Fratercula arctica Pâl Very Abundant Breeder 59 trapped 1936-1976: 5411 trapped, 2011-2014: 377 trapped, 11 retrapped, 1 control

The first record of the season was of 17 birds rafting off the Neck during the morning of 17th March; this was nine days earlier than the first of 2014 but two days later than in 2013. There were raft counts of 242, 12 and 191 over the following three days, eight on the 22nd and 1386 on the 23rd. The only other March records were of 501 on the 27th, when birds were wheeling but not landing, and of 730 on the 28th, when birds remained on the sea. Daily counts were made from around the Neck each evening, from 31st March until 31st May, to record the pattern of colony attendance (see chart below). There were 85 birds seen ashore around the Neck on 2nd April; this first observed landfall was two days later than in 2014 but four days earlier than in 2013. April counts varied dramatically with whole Island totals of 3617 on the 2nd, 3364 on the 6th, 3132 on the 14th, 4769 on the 21st and 3066 on the 28th but lows of 65 on the 4th, two on the 11th and 76 on the 18th.

The number of Puffins seen from the Neck between 31st March and 31st May 2015. The transect began from a line due north of North Haven and finished at Peter’s Bay. 2800 2600 Land 2400 Air 2200 Sea 2000 1800 1600 1400 1200 1000 800 600 400 200

0

02-Apr 04-Apr 06-Apr 08-Apr 10-Apr 12-Apr 14-Apr 16-Apr 18-Apr 20-Apr 22-Apr 24-Apr 26-Apr 28-Apr 30-Apr

31-Mar

02-May 10-May 06-May 08-May 12-May 14-May 16-May 18-May 20-May 22-May 24-May 26-May 28-May 30-May 04-May The whole Island count of 14th May coincided with the highest count achieved from the Neck. The 6665 birds logged was a huge 31.5% increase on the 5070 individuals logged on 10th April 2014, perhaps primarily due to the weather preceding the count rather than an actual increase in the population. The sea state for every day between the 2nd and 12th May was logged as either rough or very rough, largely as a result of southwesterly gales. Although the weather calmed considerably on the 13th, a substantial swell continued to roll in. Following heavy overnight rain, the wind veered to the northwest on the 14th, the sea was calm and Puffins arrived en masse. Although the whole Island counts provide a reliable long-term method for monitoring trends in numbers, how the totals reflect

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the Skokholm breeding population is difficult to ascertain. Interestingly the Crab Bay count for the evening of the 14th was fewer than 1800 birds, however more focused monitoring at this site revealed a study population of 80 burrows in an area which comprises approximately 10% of the colony and where less than half of the active burrows in that area were study burrows; thus we might predict a very rough minimum of 1600 pairs for Crab Bay (as active burrow distribution is apparently quite even) and expect nearly twice the number of birds to be using this area of sea than were logged during the whole Island count.

The maximum number of Puffins recorded each year during the period 1989-2015. 7000 6500 6000 5500 5000 4500 4000 3500 3000 2500 2000 1500 1000 500

0

1989 2003 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015

A productivity plot was established at Crab Bay in 2013 and the same area was studied during the 2015 season; the same 100 burrows individually numbered in 2013 were again used this year with the exception of two where the marker posts, lost during the winter, were repositioned. Of these, 80 were seen to be occupied and were visible throughout the season (76 in 2014); productivity estimates are based on observations of these burrows. Four active burrows (5.00%) were not seen to be provisioned with fish and it is assumed that these failed at egg stage (6.58% in 2014). The first fish provisioning on Skokholm was witnessed on 31st May (3rd June in 2014 and 30th May in 2013), but it was not until 2nd June when fish were seen to be delivered to the study plot (9th June in 2014 and 2013). Fish deliveries were earlier this year than in the preceding two years and more birds were seen to first provision young in the same short period, perhaps suggesting a more synchronised breeding period this year (see graph below). The following table shows the number of days between first and last fish provisioning for each of the 76 study burrows where a chick hatched.

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The number of days between first and last observed chick feeding. Days 1-5 6-10 11-15 16-20 21-25 26-30 31-35 36-40 41-45 46-57 No. of burrows 6 5 2 1 12 6 20 7 11 6

The number of study burrows which had been provisioned with fish by a particular date. 80 70 60 50 40 2013 30 2014 20 2015 10

0

01-Jul 02-Jul 03-Jul 04-Jul 05-Jul 06-Jul 07-Jul 08-Jul 09-Jul

02-Jun 03-Jun 04-Jun 05-Jun 06-Jun 07-Jun 08-Jun 09-Jun 10-Jun 11-Jun 12-Jun 13-Jun 14-Jun 15-Jun 16-Jun 17-Jun 18-Jun 19-Jun 20-Jun 21-Jun 22-Jun 23-Jun 24-Jun 25-Jun 26-Jun 27-Jun 28-Jun 29-Jun 30-Jun 01-Jun Although the study plot was monitored every day, it cannot be assumed that the first and last fish provisioning was seen for each burrow. Indeed the 24 hour Puffin watches highlighted how many burrows are only provisioned once during daylight hours and how occasionally some chicks are not fed at all (see table below). Puffins can fledge having spent a minimum of 34 days as a burrow-bound chick, although this is more typically 38 days and can be anything up to 60 days (Ferguson-Lees et al., 2011). However, taking into account that some deliveries may have been missed, the same assumption made in 2013 and 2014 is used, namely that a chick which was seen to be provisioned for 31 days or more was of fledging size. Thus, of the 80 monitored breeding attempts, 44 (55.0%) were potentially successful (50.0% in 2014 and 49.4% in 2013).

While this productivity estimate represents birds which have reached fledging size, fledging success is very difficult to ascertain reliably. Puffin chicks are particularly vulnerable when exercising their

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flight muscles at the burrow entrance prior to fledging and when making the journey to the sea. Great Black-backed Gulls were seen patrolling within the colonies during the chick provisioning period and were regularly observed taking young Puffins. A Lesser Black-backed Gull was also seen to take a large puffling, although after taking 15 minutes to dispatch the chick the gull was unable to break into the corpse and abandoned it (it was later found by Great Black-backed Gulls).

The number of fish deliveries to known active burrows during five daylight watches. No. of deliveries 0 1 2 3 4 5 6 7 8 9 10 11 12 14 17 No. of burrows 9 June 1 13 12 8 9 8 6 2 3 No. of burrows 18 June 3 9 11 6 3 10 13 6 5 1 2 1 No. of burrows 1 July 3 8 5 5 8 7 7 8 4 2 2 1 2 1 1 No. of burrows 12 July 3 11 4 3 9 4 3 4 1 3 2 1 No. of burrows 22 July 1 6 3 1 2 1 2 1 1

Five 24 hour watches were made (on the 9th and 18th June and the 1st, 12th and 22nd July), to monitor kleptoparasitism by gulls. The study plot was again confined to the area of the 100 numbered burrow stakes at Crab Bay. On 9th June 699 Puffins arrived to the study area with fish and of these 43 (6.15%) were successfully robbed. On 18th June 927 birds arrived and of these 34 (3.67%) were robbed. On 1st July 916 birds arrived and 23 (2.51%) were robbed. On 12th July 521 birds arrived and ten (1.92%) were robbed. On 22nd July 123 birds arrived and four (3.25%) were robbed. It should be noted that these figures do not take into account the number of fish lost to gulls at sea or on the approach to the colony. The peak in monitored kleptoparasitism in 2014 was 10.69%, recorded on 21st June, with between 0.45% and 7.21% of deliveries lost to the gulls over four further dates. In 2013 an 18.4% loss was recorded on 16th June, with between 5.25% and 10.28% of deliveries lost to the gulls on three further dates. Although the proportion of Puffins losing their fish to gulls was thus low in 2015, this is in part a reflection of more deliveries during the study period; the 43 robberies logged on 9th June was more than on any other watch in any year, but it came on a day when there were more deliveries than during any watch in 2014 or 2013.

The number of chick provisioning attempts during daylight on the 9th and 18th June, along with the number of times that gulls successfully robbed the fish. 100 90 8 (1.14%) Robbed by Great Black-backed Gull 80 35 (5.01%) Robbed by Lesser Black-backed Gull 70 60 699 (93.85%) Successful 50 40 30 20 10 0 80 70 1 (0.11%) Robbed by Herring Gull 60 11 (1.19%) Robbed by Great Black-backed Gull 50 22 (2.37%) Robbed by Lesser Black-backed Gull 40 927 (96.33%) Successful 30 20 10

0

0800-0830 2100-2130 0500-0530 0600-0630 0700-0730 0900-0930 1000-1030 1100-1130 1200-1230 1300-1330 1400-1430 1500-1530 1600-1630 1700-1730 1800-1830 1900-1930 2000-2030 2200-2230 0400-0430 25 | Skokholm Seabird Report 2015

The number of chick provisioning attempts during daylight on the 1st, 12th and 22nd July, along with the number of times that gulls successfully robbed the fish. 90 80 2 (0.22%) Robbed by Herring Gull 10 (1.09%) Robbed by Great Black-backed Gull 70 11 (1.20%) Robbed by Lesser Black-backed Gull 60 916 (97.49%) Successful 50 40 30 20 10 0

50 40 10 (1.92%) Robbed by Lesser Black-backed Gull 521 (98.08%) Successful 30 20 10 0 15 4 (3.25%) Robbed by Lesser Black-backed Gull 10 123 (96.75%) Successful

5

0

0800-0830 1900-1930 0400-0430 0500-0530 0600-0630 0700-0730 0900-0930 1000-1030 1100-1130 1200-1230 1300-1330 1400-1430 1500-1530 1600-1630 1700-1730 1800-1830 2000-2030 2100-2130 2200-2230

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A colour ringing project was begun at Crab Bay in 2011 to allow an estimate of adult survival to be made each year. There were 128 birds ringed in the first year, 58 in 2012, 51 in 2013 and 57 in 2014. Of the 2011 birds, there were 72 seen in 2012, 98 seen in 2013, 83 seen in 2014 and 73 were recorded this year. By comparing the resighting records of the past four years, it is evident that 108 (84.38%) of the 128 ringed were actually still alive in 2012, 105 (82.03%) were alive in 2013 and 88 (68.75%) were alive in 2014, although not necessarily at the colony in those years. A flaw with this survivorship estimate is that colour marks were added to Puffins caught in flight, individuals potentially resident in areas not visible to researchers. A better estimation of survivorship may therefore come from looking for birds previously seen in the field; thus of 108 birds alive in 2012, 105 (97.22%) were alive in 2013, but only 88 (81.48% of the 2012 total and 83.81% of the 2013 total) were recorded in 2014, a substantial drop in resightings (and presumably adult survival) thought to be attributable to the prolonged storms of the 2013-2014 winter. Interestingly, despite a winter with fewer dead bird reports and an increased whole Island count, only 82.96% of the 2011 birds logged in 2014 were encountered this year, a very similar decline to that seen in 2014.

It would seem that the low return rate of birds ringed in 2011 may not be representative of the study area as a whole. Of the 58 birds ringed in 2012, there were 54 (93.10%) known to be alive in 2013 and only 38 (65.52% of the 2012 total and 70.37% of the 2013 total) were recorded in 2014, again presumably a reflection of the winter storms. However this year there were 36 birds logged (94.74% of the 2014 total), a return rate much closer to what would be expected in a typical year and well above the 82.96% of 2011 ringed birds encountered. Likewise, of the 51 birds ringed in 2013, only 39 (76.47%) were recorded after the severe winter but 89.74% of those seen in 2014 were also seen this year. Of the birds ringed in 2014, 87.72% were seen this year, despite the issues with catching birds in flight which may nest in hidden areas. These year of ringing dependent differences in return rate may reflect differences in the survival of different ages of bird, although data will be needed from more years to investigate this further.

The end of July saw fewer birds arriving with fish, although there were still large numbers of adults offshore including 3050 on the 24th and 4700 on the 26th when approximately 3500 were rafting to the north of the Neck. There were 1260 birds logged on 1st August, 256 on the 2nd, 228 on the 4th and 98 on the 5th. There were then low double figure counts until the 9th and three were logged on each of the next three dates. There were no birds logged on the 13th, 14th or 15th, although two were seen bringing fish into the same area of South Haven on the 16th. This last record of chick feeding was seven days earlier than in 2014 but two days later than in 2013. A lone bird was seen in Broad Sound on 26th September, mirroring the single autumn record of 2014 logged there on 22nd September.

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Razorbill Alca torda Llurs Abundant Breeder 27 trapped (including 23 pulli) 1936-1976: 9220 trapped, 2013-2014: 56 trapped, 1 retrapped, 2 controls

In contrast to the slow return observed following the wrecks of the 2013-2014 winter, this year saw birds on the cliffs from the arrival of staff on 5th March and peak March counts similar to those of 2013; there were highs of 2380 on the 15th, 2074 on the 16th and 1441 on the 23rd, compared with 2014 highs of 1145 on the 27th and 1079 on the 28th and 2013 highs of 2069 on the 20th and 1818 on the 27th. However their presence was still sporadic, with no birds logged during very wet weather on the 8th, 9th and 12th and fewer than ten logged during gales on each of the last three days of the month. April attendance was similarly irregular, with highs of 1739 on the 2nd and 1751 on the 15th but lows of only 117 on the 1st, five on the 10th, 35 on the 12th, 19 on the 17th and 13 on the 18th. Although counts were more consistent towards the end of the month, these were often bolstered by rafting birds; there were only 43 on ledges on the 26th and 204 on ledges on the 28th. Nevertheless an early egg was found along the South Coast on the 27th, 16 days earlier than the first of 2014 and 14 days earlier than in 2013; interestingly the start of the breeding season was also earlier in the other two auk species this year. May counts were consistently high from the 6th onwards, although there were large scale departures for the sea on the 2nd, when only 112 remained on ledges, and the 5th, when only 270 remained.

Six study plots, established in 2002, were visited on ten dates between the 4th and 14th June and every adult in suitable breeding habitat was counted. There was a 15.3% increase in numbers compared with 2014 and the mean total of 316 adults on ledges was the second highest on record. Interestingly three of the largest plots, at Little Bay Point, Twinlet Bay and North Gully, saw totals very similar to the record counts of 2013 (9.7% down, 3.1% down and 6.7% up respectively), whereas the plot at Middlerock saw a total 19.8% down on 2013 and exactly the same as the 2014 count which followed the winter wrecks. Quite why the Middlerock plot did not bounce back in the manner seen elsewhere is unclear. The plot counts are significantly affected by the weather; in the unsettled June of 2012 the total fluctuated between 164 and 338 birds whereas the ranges during the calmer 2013 and 2014 surveys were considerably smaller, with a 2013 low of 301 and a high of 397 and a 2014 low of 254 and a high of 315. This year again saw a study period dominated by high pressure and the ten counts exhibited the narrowest range observed in the last four seasons; there was a low of 291 on the 9th and a high of 346 on the 14th. It thus seems likely that the 2015 counts

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reflect a genuine increase in the number of birds attending the colonies, although it is unclear whether this was due to the return of birds which did not breed following the severe winter of 2013- 2014 or whether it reflects the recruitment of new birds to the breeding population.

The total number of adult birds in all six study plots 2002-2015 (as an average from ten visits) and the totals from the four largest plots (as an average from ten visits). 400 Total 346 350 Plot 1 316 302 Plot 2 300 274 Plot 3 246 256 251 Plot 5 235 250 207 207 193 200 168 166 173 150

100

50

0

2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015

Whole Island counts were made during early June and counts were made from a boat on 16th June. This is the third year running that access to a boat has been available, inevitably leading to higher but more accurate whole Island counts; in 2012 rough seas meant that there was no opportunity for a boat based count and it was concluded that ‘there remains a section of North Coast that was missed, while other parts of the North Coast and Bluffs were counted less accurately at a distance’ (Gillham and Yates, 2012). A whole Island total of 2382 adults on suitable breeding ledges this season was 16.1% up on the 2052 logged in 2014 and was the highest total yet recorded on Skokholm (3.8% up on the previous highest total of 2294 logged in 2013).

The total number of Razorbills (adults on ledges) recorded on Skokholm since 1970 and the number of birds within the study plots since 2002. 2500 2250 2000 1750 1500 1250 1000 750 500 250

0

1989 2002 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 1969

The increase in the whole Island count mirrored that observed in the plots, with the plot total making up 13.3% of the whole Island total for a second year. Previous Skokholm seabird reports have detailed how the weather has a significant bearing on the number of birds logged; fine weather perhaps attracts more non-breeding birds, allows adults to hunt more effectively and thus spend more time at the colony, or perhaps birds prefer to spend periods of poor weather at sea. The weather during the 2015 survey was again set fair and it would thus seem likely that the counts were both accurate and directly comparable with 2013 and 2014 when good weather again dominated

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the study period. However it should be noted that in May there were ten days of heavy rain and 13 days when the sea was logged as rough or very rough, conditions which may have seen more pairs than normal fail prior to the counts (see productivity estimates below).

The whole Island totals, plot totals and the percentage of the Island totals made up of study plot birds (*includes a boat based count). 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Island - 992 937 812 946 950 1140 1486* 1463 2294* 2052* 2382* Plots 166 173 207 207 246 235 256 302 251 346 274 316 Plot % - 17.4 22.1 25.5 26.0 24.8 22.5 20.3 17.2 15.1 13.3 13.3

Productivity monitoring was undertaken for a third year running and the same two study sites were used, one a cliff below the Neck Razorbill Hide where 30 incubating pairs were located by 31st May and one a site among the Bluffs boulder slope where 34 egg sites were marked on 24th May. Among the Bluffs boulders 16 pairs failed at egg stage, with at least one egg found to be coated in thick mud following exceptionally heavy rain. A further eight pairs failed with chicks, one of which was found dead at the nest site, presumably due to exposure during further heavy rain or a lack of food, but not predation. One of the eight was found to have its intestines on the outside of its abdomen, a condition which in chickens has been linked to very cold temperatures around the period of hatching. There were ten pairs (29.41%) which produced a jumping sized chick (0.29 young per pair), which is 34.1% down on the 0.44 recorded at this site in 2014 and 47.3% down on the 0.55 of 2013. On the cliff there were 17 failures at egg stage and eight failures at chick stage; although the reason for failure was typically unclear, two sites were seen to contain smashed eggshell, an egg on 11th May was pushed from the cliff by an aggressive pair usurping the nest ledge and an egg on 18th May was accidentally lost during an incubation changeover. Five pairs which lost eggs were assumed to have produced a second egg, due to a continued presence and the appearance of eggs in exactly the same sites; of these four failed again, three at egg stage and one with a small chick, whilst one pair reared a chick to jumping size. The chick of this successful relay attempt was last seen on 24th July and was the last chick to be seen anywhere on the Island this year. In total there were five jumping sized chicks at the Neck site (0.17 per pair), a figure 52.8% down on the 0.36 per pair recorded at this plot in 2014 and 77.9% down on the 0.77 per pair recorded in 2013.

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This is the second year running that productivity has been significantly higher in the boulder plot than on the cliff, although the 0.77 chicks per pair logged at the cliff in 2013 is the highest productivity observed at either plot in any of the last three years. Both sites were again significantly down this year, with a combined productivity figure of 0.23 jumping sized chicks per monitored pair (0.39 in 2014 and 0.67 in 2013); it is unclear whether this reflects poor adult fitness, the impacts of unfortunately timed severe weather during the breeding season, a change in predation pressure or a combination of factors. Both Herring and Great Black-backed Gulls were observed taking Razorbill chicks, although a substantial increase in the time spent watching the colony would be required to ascertain the impact of these predators. For a third year running the last of the breeding attempts within the boulders were concluded before the last of the attempts on the cliffs. This perhaps reflects a tendency for large chicks among the boulders to move away from the egg site, whilst cliff chicks have little room for movement; however there are genuinely fewer chicks anywhere within the boulder field when compared with the cliff towards the end of the breeding season.

The number of adults on ledges within three of the plots (standard study period in black). 110 Middlerock 100 Guillemot Cliff 90 North Gully 80 70 60 50 40 30 20 10

0

02-Jul 04-Jul 06-Jul 08-Jul 10-Jul 12-Jul 14-Jul 16-Jul 18-Jul 20-Jul 22-Jul

26-Jun 30-Jun 06-Jun 08-Jun 10-Jun 12-Jun 14-Jun 16-Jun 18-Jun 20-Jun 22-Jun 24-Jun 28-Jun 04-Jun

For a second year running counts at three of the study plots were continued beyond the normal study period to ascertain the pattern of colony attendance during the remainder of the breeding season (see graph above). There were fluctuating numbers in all three colonies and notable peaks where the totals were presumably supplemented by the return of failed adults or the presence of more non-breeding birds; interestingly these peaks frequently coincided between colonies suggesting that the birds respond to the same environmental cues. The first fledgling had departed by 26th June and within the study plots 60% of the fledglings had departed by 30th June; it was not until 7th July that 60% of young had jumped in 2014. The remaining study chicks had fledged by 4th July, with the exception of the relay at the Neck plot which did not hatch until 2nd July and did not jump until the night of the 24th (11 days later than the last of 2014). There was a similar departure of adult birds, with numbers dropping rapidly from 30th June. There were only double figure counts from 8th July (17th July in 2014 and 14th July in 2013) and these had dropped to single figure counts by the 22nd (27th in 2014 and 24th in 2013). Adults were last seen on the cliffs on 24th July, seven days earlier than in 2014 and three days earlier than in 2013. There were only 18 birds logged over eight dates in August and in September there were 67 logged over six dates from the 4th. October counts were up on 2013 but down on the 689 logged over 22 dates in 2014; this year there were 162 logged over 18 dates with a peak of 69 on the 17th. Numbers remained low in November, with 22 on the 12th the highest count. Further large auks were present at sea during the autumn but their distance

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from land saw them logged as ‘auk sp.’; there were 606 in September, 672 in October and 1031 between the 1st and 26th November including a peak of 309 on the 16th.

Guillemot Uria aalge Gwylog Abundant Breeder 1 pullus trapped, 5 controls 1936-1976: 1023 trapped, 2013-2014: 1 pullus trapped, 7 controls

Birds were already present upon the return of staff, with a minimum of 930 logged along the North Coast cliffs on 5th March. The pattern of colony attendance during the month was surprisingly different to that observed for Razorbill; although both large auks were in very low numbers on 13 dates and abundant on eight dates, there were five dates when few Guillemots returned but the Razorbill count was in four figures and one date when 1450 Guillemots returned but only 30 Razorbills. Birds took to the ledges on ten dates during the month (seven dates in 2014 and four dates in 2013) and there were peak counts of 2251 on the 16th, 2008 on the 17th and 2727 on the 18th, the highest March counts ever logged on Skokholm. Birds were more regular in April than in the previous two seasons; although there were low counts on 13 dates, including total absences on the 10th, 17th and 18th, there were low counts on 19 dates in 2013 and 2014. Over 1000 birds were logged on 14 dates during the month, including peaks of 2617 on the 2nd, 3315 on the 15th and 2666 on the 22nd. Whereas the last two seasons have seen colony attendance continue to fluctuate during the first half of May, this season saw consistently high totals from the 3rd following a low of only 215 individuals on the 2nd. Although only 28 birds were logged on the ledges on the 2nd, this included the first bird to be seen incubating an egg in 2015; this was 13 days earlier than the first egg record of 2014 and 11 days earlier than the first of 2013.

The six study plots were counted on ten dates between the 4th and 14th June. The mean total from all plots was close to the previous two seasons, just five birds (0.6%) up on 2014 and 32 birds (3.6%) down on 2013. Three of the six plots contained very similar numbers to 2014; the Little Bay Point plot mean was 1.6% up on 2014, the Middlerock plot was 1.6% up and one of the Steep Bay Point plots was identical. There were increases at North Gully, where there were 6% more birds than in

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2014 and just seven fewer than the 271 logged in the record year of 2013, and at the other Little Bay Point plot where a 10% increase took the mean back to the record of 44 logged in 2013. The Guillemot Cliff plot contained a mean of 181 individuals in 2013 and 180 individuals in 2014, however this year there was a 9.4% drop to 163 birds. The 2015 study period was again dominated by high pressure and saw a low of 756 and a high of 939 individuals within the plots (a range of 183 individuals); despite the settled weather, there was thus more variation in the counts than in 2014 and 2013 when the highest and lowest counts differed by 150 and 125 individuals respectively. In the wet and unsettled June of 2012 the total fluctuated between 530 and 746 birds, a range of 216 individuals.

The total number of adult birds in all six study plots 2002-2015 (as an average from ten visits) and the totals from the four largest plots (as an average from ten visits). 1000 Total 896 859 864 900 Plot 1 800 Plot 3 Plot 4 700 613 625 Plot 5 556 557 600 447 445 463 500 400 360 400 261 300 200 100 0 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015

These counts of individuals potentially include incubating adults, some of their mates, failed breeders, non-breeding adults and younger birds yet to breed; a correction factor is thus sometimes adopted to convert this count of individuals to an estimate of breeding pairs (Harris et al., 2015). To check the correction factor is a time consuming task as it requires very regular colony watches over the entire egg laying period to assess how many eggs are produced. This year saw such a study undertaken by two volunteers at the North Gully plot where an average of 264 individuals was logged over the ten study plot visits. Daily visits to the plot revealed 151 eggs and a further 19 individuals which were apparently incubating but where their position in the colony meant that an egg could not be seen. If it is assumed that 170 pairs incubated an egg, a correction factor of 0.64 would be used to convert the number of individuals logged to breeding pairs. This is very similar to the 0.67 widely adopted in previous studies and which is apparently still suited to areas where the population is increasing; a declining population requires a higher correction factor (Harris et al., 2015).

Whole Island counts were made during early June and calm weather, along with access to a boat, allowed for counts to be made from the sea on 16th June. Boat-based surveys allow some areas to be monitored which cannot be viewed from on the Island and enable closer access to some areas which can normally only be viewed at a distance. A total of 3603 adults in suitable breeding habitat was a 2.6% increase on the 2014 count and the highest total yet recorded on Skokholm. This is the third year running that a small increase in the population has been noted following the significant increase observed over the past decade. The percentage of the whole Island count made up of study plot birds dropped for a sixth consecutive year, although this will in part reflect the increased coverage of boat-access areas. It should be noted that in May there were ten days of heavy rain and 13 days when the sea was logged as rough or very rough; during this period the more exposed

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Guillemot colonies were awash with significant amounts of water, conditions which may have seen more pairs than normal lose eggs prior to the counts (see photograph above).

The whole Island totals, plot totals and the percentage of the Island totals made up of study plot birds (*includes a boat based count). 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Island 1202 - 1348 1455 1538 1697 1795 2212* 2330 3466* 3512* 3603* Plots - 400 447 445 463 556 557 613 625 896 859 864 Plot % - - 33.2 30.6 30.1 32.8 31.0 27.7 26.8 25.9 24.5 24.0

The total number of Guillemots (adults on ledges) recorded on Skokholm since 1928 and the number of birds within the study plots since 2002. 3600 3300 3000 2700 2400 2100 1800 1500 1200 900 600 300

0

1929 1931 1933 1935 1937 1939 1941 1943 1945 1947 1949 1951 1953 1955 1957 1959 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015 1927

A survey undertaken on 21st May by Professors Mike Harris and Sarah Wanless found that, of 1644 birds on ledges, there were 13 ‘bridled’ individuals. Combined data from Skokholm and Skomer in 1981 revealed 11 ‘bridled’ birds in a sample of 760 (Birkhead, 1984); ‘bridled’ birds thus made up 1.44% of those studied, a proportion not significantly different to the 0.79% found this year.

The first chick to be seen this season was found on the Neck on 7th June, six days before the first of 2014 and seven days before the first of 2013. Productivity, calculated at between 0.55 and 0.61 chicks per pair in 2013 and 0.6 in 2007, was not assessed in 2015 in accordance with recommendations from the Islands Conservation Advisory Committee. Chicks were observed jumping from 25th June and the number of adults recorded in the cliff plots dropped rapidly from 679 on 29th June to 493 on 1st July, 407 on the 7th, 258 on the 9th, 151 on the 14th, 26 on the 16th and the last three birds were seen on 18th July (22nd July in 2014 and 28th July in 2013). Whole Island

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counts mirrored those taken at the plots and a lone brooding bird at the Neck on 25th July was the last to be seen ashore. There were small numbers offshore in late July with 92 logged on the 20th, 51 on the 23rd and 44 on the 26th. There were 81 Guillemots logged over 14 dates in August including calling youngsters heard from the Lighthouse and peaks of 23 on the 26th and 16 on the 27th.

The number of adults on ledges within three of the plots (standard study period in black). 300 275 Middlerock 250 Guillemot Cliff 225 North Gully 200 175 150 125 100 75 50 25

0

22-Jul 02-Jul 04-Jul 06-Jul 08-Jul 10-Jul 12-Jul 14-Jul 16-Jul 18-Jul 20-Jul

06-Jun 08-Jun 10-Jun 12-Jun 14-Jun 16-Jun 18-Jun 20-Jun 22-Jun 24-Jun 26-Jun 28-Jun 30-Jun 04-Jun September counts were well down on 2014 with only 57 birds logged over 17 dates and peaks of 23 on the 13th and six on the 22nd, although a further 606 unidentified large auks were logged at sea during the month. There were only 25 birds logged over five dates in October, with a high of eight on the 5th and a further 672 large auks noted offshore. Although a return of Guillemots to the breeding ledges in early winter is to be expected, there has been no record of this on Skokholm for more than a decade. In November 2014 staff departed on the 24th and in 2013 the departure was on the 16th; although these were the latest departure dates for several years, Guillemots had not returned to the cliffs before recording ceased. This November there were 83 birds logged over eight dates to the 12th and 26 logged on the 16th included six birds on a ledge to the west of North Gully. There were 148 birds logged at sea over the following three days and 420 were ashore on the 20th. Interestingly the birds which came ashore on the 20th were occupying just two areas, the cliff to the west of North Gully and a cliff at Little Bay Point; if it is assumed that the birds take to the same ledges which they will occupy in the breeding season, then it would seem likely that these neighbours must first congregate at sea to coordinate their visit. Birds were logged on six more dates during the month, including highs of 367 on the 23rd and 790 on the 24th during which time 840 birds, some in winter plumage and some in breeding plumage, were seen ashore. On each date when a substantial landing occurred, on the 20th, 23rd and 24th, at least one bird was taken by a Peregrine. A return to the colony outside of the breeding season, with the risk of being predated, must thus have a substantial benefit; it has been suggested that the return may be to secure the best breeding ledges and thus secure the best mate (Harris et al., 2005), but birds ashore may also use less energy than those at sea (Humphreys et al., 2007).

Ringing recovery Left leg green darvic with white 69K, Right leg N00620 Originally ringed as a chick, SKOMER ISLAND, PEMBROKESHIRE 2005 Previously recovered as an adult, SKOMER ISLAND, PEMBROKESHIRE four times in 2009 Previously recovered as an adult, SKOMER ISLAND, PEMBROKESHIRE 11 times in 2010 Previously recovered as an adult, SKOMER ISLAND, PEMBROKESHIRE seven times in 2011 Previously recovered as an adult, NORTH GULLY, SKOKHOLM 5th May 2014 Recovered as an adult, NORTH GULLY, SKOKHOLM 29th April 2015 Finding condition Ring read in field

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Distance travelled 4km at 163 degrees (SSE) Days since ringed approximately 3590

Ringing recovery Left leg blue darvic with white 11K, Right leg N00712 Originally ringed as a chick, SKOMER ISLAND, PEMBROKESHIRE 2004 Previously recovered as an adult, SKOMER ISLAND, PEMBROKESHIRE 21st May and 10th June 2009 Previously recovered as an adult, NORTH GULLY, SKOKHOLM 4th May 2014 Recovered as an adult, NORTH GULLY, SKOKHOLM 29th May 2015 Finding condition Ring read in field Distance travelled 4km at 163 degrees (SSE) Days since ringed approximately 3985

Ringing recovery Left leg white darvic with black 24A, Right leg N03025 Originally ringed as a chick, SKOMER ISLAND, PEMBROKESHIRE 2006 Previously recovered as an adult, SKOMER ISLAND, PEMBROKESHIRE once in 2009 Previously recovered as an adult, SKOMER ISLAND, PEMBROKESHIRE twice in 2010 Previously recovered as an adult, NORTH GULLY, SKOKHOLM 2011 Recovered as an adult, NORTH GULLY, SKOKHOLM 17th March 2015 Finding condition Ring read in field Distance travelled 4km at 163 degrees (SSE) Days since ringed approximately 3180

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Ringing recovery Left leg N03245, Right leg blue darvic with white 649 Originally ringed as a chick, SKOMER ISLAND, PEMBROKESHIRE 2007 Previously recovered as an adult, SKOMER ISLAND, PEMBROKESHIRE 15th May and 12th June 2010 Previously recovered as an adult, SKOMER ISLAND, PEMBROKESHIRE 13th May and 3rd June 2011 Previously recovered as an adult, NORTH GULLY, SKOKHOLM 5th May 2014 Recovered as an adult, NORTH GULLY, SKOKHOLM 14th April 2015 Finding condition Ring read in field Distance travelled 4km at 163 degrees (SSE) Days since ringed approximately 2845

Lesser Black-backed Gull Larus fuscus Gwylan Gefnddu Leiaf Abundant Breeder previously very abundant breeder 61 trapped (including 28 pulli), 3 retrapped, 3 controls 1936-1976: 12,085 trapped, 2013-2014: 269 trapped, 5 retrapped, 8 controls

The 19871 birds logged this March was somewhat down on the 23157 logged during March 2014. Peak counts were also down, with highs of 1501 on the 13th, 1361 on the 27th and 1135 on the 29th compared with four counts of over 1500 in 2014. However there were 12 days when birds were noted coming in to roost at dusk and it is very likely that more individuals were overnighting than were logged. Large roosts did not form every night and there were low counts of 348 on the 11th, 200 on the 12th, 386 on the 15th and 686 on the 25th when the majority of birds stayed away from the Island. The GPS trackers fitted by the British Trust for Ornithology in 2014 (funded by the Department of Energy and Climate Change), revealed how birds returned for the breeding season; of 18 tracker birds which returned with functioning tags, four had returned to Skokholm before the end of February, a further seven before 15th March, a further five before the end of March and there were two birds which did not return until April. Although the three birds which overwintered in Pembrokeshire returned first, the return dates of the other birds were not seemingly influenced by overwintering site; some of the longer distance migrants returned before those which had wintered in France. The return dates seem to suggest that female birds return to the colony before the males.

When GPS tagged Lesser Black-backed Gulls made their return to Skokholm. Tracker Overwintering Departed Departed Arrived to Sex Number Location Overwintering Mainland Skokholm Location Europe 4022 Pembrokeshire 1st February Female 4023 Pembrokeshire 8th February ? 5004 Pembrokeshire 9th February Female 5003 Central Spain 19th February 24th February 27th February Female 5000 Northwest France 22nd February 28th February 4th March Female 5001 South & Central Spain 1st March 3rd March 4th March Female 4024 South Spain 28th February 7th March 8th March Male 5013 Northwest Morocco Missing data 10th March 11th March Female 5021 Midwest Portugal 3rd March 11th March 12th March Female 5009 South Spain 5th March 11th March 12th March Female 5010 Northwest Spain 22nd February 11th March 13th March Female 5002 Northwest France 9th March 11th March 16th March Female 5006 Northwest France 17th March 17th March 17th March Female 4000 Northwest Morocco 7th March 16th March 18th March ? 5017 Midwest Portugal 5th March 12th March 19th March Male 5022 Central Spain 1st March 16th March 20th March Male 4009 Midwest Portugal 28th March 3rd April 4th April Male 5015 Northwest Morocco 28th March 11th April 13th April Male

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Some of the different strategies used by overwintering Lesser Black-backed Gulls. The tracker numbers match those given in the above table.

4022 5006

5003 5022

5001 4000

Google Imagery © 2014 TerraMetrics

Numbers logged in April were relatively consistent, although there were occasional mass departures and low counts of 439 on the 5th, 450 on the 6th, 462 on the 10th, 473 on the 13th, 458 on the 18th and 391 on the 20th. The first eggs were found on 4th May when the majority of nests near North Pond were empty but two contained three eggs and three contained a single egg; these eggs were 11 days

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later than the first record of 2014 (but only a single egg was found on that date) and one day later than in 2013 (when two nests contained two eggs).

Vantage point counts of all the inland breeding colonies and a full census of the coast nesting pairs were made on the 22nd and 23rd May, during which 1275 apparently incubating adults (aia) were located. Walk through counts were undertaken at six subcolonies on the 24th to check the accuracy of the counts. A comparison of the number of apparently incubating adults and the number of nests containing eggs suggested that there was a discrepancy (see table below). In one area of shorter vegetation north of Frank’s Point there were 5.67% fewer nests with eggs than the number of apparently incubating adults, presumably due to sitting guard birds or non-breeders appearing as if they were incubating or due to birds sitting on empty nests. Conversely, the majority of subcolonies contained more nests with eggs than the number of apparently incubating adults, presumably due to incubating birds being hidden in vegetation. In other areas with shorter vegetation, to the North of the Wheelhouse, to the north of the Top Tank and to the south of North Pond, the vantage point and walk-through counts were very similar, differing by just three or fewer nests. However areas of longer vegetation to the west of Orchid Bog and to the north of Bread Rock hid considerably more nests from the vantage point counters; on average there were 25% more nests with eggs than the number of incubating birds seen (there were 12.89% more in 2014, a year when the vegetation was not as thick as witnessed this year). A correction factor of 1.25 was thus applied to the inland colonies with similar dense vegetation, but not to the cliff counts and areas of very short sward. The corrected total was 1486 pairs. The 1275 apparently incubating adults counted during the vantage point survey is 9.7% down on the 1407 recorded in 2014 and 13.6% down on the 1476 recorded in 2013. The corrected total is 5.0% down on the 1565 pairs logged in 2014 and is very similar to the 1476 of 2013. The walk through areas at the Top Tank and Frank’s Point were exactly the same as used in 2014; at the Top Tank there were 16 fewer nests and six fewer nests with eggs and at Frank’s Point there were six more nests and five more nests with eggs. The 2013 whole Island total was the lowest for over 40 years and there has seemingly been little change since.

A comparison of vantage point counts (of apparently incubating adults) and walk through nest counts, along with a summary of nest contents. *how many more/less active nests were present than the number of incubating birds seen (%). Vantage Walk- Empty/ Percentage Difference Egg Eggs per point through With of empty between count nest with count count egg(s) nests counts* eggs Wheelhouse 44 aia 60 nests 15/45 25.00% +2.27% 94 2.09 Top Tank 84 aia 94 nests 7/87 7.45% +3.57% 243 2.79 North Pond 84 aia 106 nests 20/86 18.87% +2.38% 224 2.60 Orchid Bog 53 aia 87 nests 13/74 14.94% +39.62% 186 2.51 Frank’s Point 141 aia 148 nests 15/133 10.14% -5.67% 356 2.68 Bread Rock 87 aia 141 nests 40/101 28.37% +16.09% 240 2.38

Over the period 1991-2002 the count of empty nests varied from 11-44% of the total number of nests, with a mean of 22.7% (Thompson, 2007). With the exception of the area near the Top Tank, where less than 10% of nests were found to be empty, the number of empty nests located at each walk through site in 2015 was within the range of that found by Thompson. Overall, of 636 visited nests, 17.30% were found to be empty (16.32% in 2014 and 19.84% in 2013). It was unclear whether the empty nests were second nests made by the pairs present, nests which had been robbed of their eggs or nests where the adults had yet to lay. The breeding season was certainly a protracted one with the first chicks located below the Top Tank on 6th June (23rd May in 2014 and 30th May in 2013), other chicks just hatching on 15th July when the first fledglings were taking to the wing and a late fledgling near Orchid Bog on 13th September.

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The total number of Lesser Black-backed Gull breeding pairs 1970-2015. Control of numbers started in 1984 (destruction of nests) and stopped in 1998. 5000 4500 4000 3500 3000 2500 2000 1500

1000

1970 1981 2000 2011 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2012 2013 2014 2015 1969

The breeding success of the Skokholm Lesser Black-backed Gull population has been low for many years and is probably a major factor contributing to the observed population decline. The poor success has been linked to a reduction in food availability during the chick rearing period, primarily due to changes in the fishing industry (for example in Thompson, 2007). Studies on Skomer in the 1970s and 1980s suggested that earthworms were an important adult food item during the egg incubation period but that adults switched to taking fish during the chick provisioning period. The decline in reproductive success has been attributed to a failure to make this switch in food, with regurgitate studies suggesting that chicks are fed on earthworms in years of poor productivity. Circumstantial evidence suggested that hot, dry summers resulted in productivity being further reduced, perhaps due to earthworms being less available in dry conditions (Thompson, 2007). The 2014 tracking data suggested that the majority of adult birds did however make a switch to maritime feeding during the chick rearing period, a switch which may have been responsible for the improved productivity witnessed that season.

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This year the tracking data suggests that far fewer birds made the switch to maritime feeding in June and July, although it is not known whether the tracked birds had chicks this year. Of 17 birds which still had functioning tags during the chick feeding period, six solely fed inland, one spent the majority of one day at sea (12th June), two were at sea for two days (one for the 12th and 29th June, one for the 14th and 15th June), two were at sea for three days (10th, 15th and 16th June and 20th, 23rd and 24th June), one was at sea for four days (8th to 11th June), one was at sea for five days (five trips between the 9th and 28th June), two were at sea for six days (one making three trips between the 7th and 16th June and one on 12th July, the other making three trips between the 11th and 27th June and one on 30th July) and one made ten trips to sea (between the 6th and 30th June, but with all of July spent inland); thus 16 of the 17 birds spent the majority of the chick feeding period foraging inland and followed nearly every foraging trip at sea with a foraging trip inland. Only one bird spent the majority of time at sea, 33 days in total; following a trip to sea on the 7th and 8th June, this bird only fed inland on 21 days until the end of July. Whether the lower productivity seen this year was a result of this general lack of maritime feeding could not be proven.

Only the colony at Frank’s Point, where 17 fledging sized chicks were ringed, proved suitable for ring resighting, the ringed fledglings in other subcolonies predominantly congregating in clearings which could not be observed due to thick surrounding vegetation. The Frank’s Point plot was revisited after the fledglings were ringed and observations were made with a telescope to ascertain the number of fledglings which were ringed and the number which were definitely not ringed. A simple calculation, (number of fledglings ringed x number checked for rings on second visit)/number of birds seen to have rings on second visit, predicts the number of fledglings within the area. In 2014 it was predicted that 128 nests produced 136 fledglings (1.06 fledged young per pair), although the maximum number of fledglings seen at any one time was only 39 (giving a productivity figure of 0.30 chicks per pair). This year there were no more than 17 fledglings seen at Frank’s Point, an area which contained 133 nests with eggs (0.13 fledged young per pair). Only one fledgling was observed which did not have a ring leading to the low prediction of 19.83 fledglings for the area or 0.15 fledged chicks per pair. Observations from elsewhere also suggested that 2015 was a much poorer breeding season; for example at North Pond there were a maximum of 127 fledglings in the July of 2014 whereas this year there was a maximum of 68 recorded on the 30th and 31st.

Lesser Black-backed Gull productivity estimates. 2004 2005 2008 2011 2012 2013 2014 2015 0.07 0.27 0.27 0.03 0.16 0.16 0.30 0.15

The number of Lesser Black-backed Gulls roosting on North Plain and in the vicinity of North Pond. 600 550 500 450 400 350 300 250 200 150 100 50 0 1 5 10 15 20 25 30 5 10 15 20 25 30 5 10 15 20 25 30

July August September

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North Plain and the area around North Pond again proved to be the usual site for the largest post breeding roost, with smaller numbers congregating around the coast and at South Pond. Numbers using the site gradually increased during June from 93 on the 15th to 124 on the 21st, 142 on the 25th and 199 on the 29th. The number of birds roosting increased during July with peak counts of 320 on the 15th, 528 on the 25th and 373 on the 31st; although the peak count was thus up on 2013 and only fractionally down on 2014, there were 1413 fewer birds logged during the month than in July 2013 and 4286 fewer than in 2014, the latter drop due to the presence of considerably fewer fledglings this year. As in the preceding two years, August saw the largest roosts recorded this season with 420 on the 3rd, 402 on the 6th, 581 on the 14th and 429 on the 18th; these peaks were well down on the highs of 943 on the 21st, 800 on the 22nd and 740 on 23rd August 2014 and the 680 logged on 11th August 2013, again in part a reflection of breeding success but also a significant reduction in the number of adults present this year. There were 8903 birds logged at the North Pond and North Plain roost sites during August, down on the 9834 logged in 2013 and well down on the 13849 logged in 2014. Counts dropped off considerably during early September, as they did in 2013 when the breeding season was similarly poor, a drop which was not seen until the middle of the month in 2014. A small number of birds remained in October with records on all but nine dates and highs of 22 on the 5th and 15 on the 26th. There were single figure counts logged on the majority of days until 26th November, with a total absence noted on nine dates. However a roost of 98 birds on the 21st, all rafting with 585 Herring Gull on a flat calm sea in South Haven, was the highest November count for over ten years.

Ringing recovery Left leg orange darvic with black T090, Right leg 6135552 MADRID Originally ringed as an adult, CTRU GOMECELLO, SALAMANCA, SPAIN 26th December 2011 Recovered as an adult, EAST BOG, SKOKHOLM 13th June 2015 Finding condition Ring read in field Distance travelled 1233km (N) Days since ringed 1265 This is the second bird we have controlled from this colour ringing project following T015 which was ringed as a first-winter at the same site in 2010 and controlled on Skokholm in 2014.

Ringing recovery Left leg blue darvic with orange DTV, Right leg FH21424 Originally ringed as an adult, STOKE ORCHARD, GLOUCESTERSHIRE 22nd November 2008 Previously recovered as an adult, PINTO, MADRID, SPAIN 7th January 2009 Previously recovered as an adult, near HEMPSTED, GLOUCESTERSHIRE 23rd November 2010 Previously recovered as an adult, NORTH PLAIN, SKOKHOLM 29th July and 13th August 2013 Previously recovered as an adult, NORTH PLAIN, SKOKHOLM 29th March and 2nd September 2014

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Recovered as an adult, NORTH PLAIN, SKOKHOLM 13th March 2015 Finding condition Ring read in field Distance travelled 220km at 266 degrees (W) Days since ringed 2287 This bird has only ever been seen in unseasonal winter plumage on Skokholm.

Ringing recovery GA00721 reringed Left leg yellow darvic with black 7P:W, Right Leg GR98242 and fitted with GPS device #5002 Originally ringed as a chick, BARDSEY ISLAND, GWYNEDD 24th June 1996 Previously recovered as an adult, TOP TANK, SKOKHOLM 16th May 2014 Recovered as an adult, TOP TANK, SKOKHOLM May 2015 Finding condition device #5002 detected during breeding season Distance travelled 122km at 196 degrees (SSW) Days since ringed 6900 This bird spent much of the winter in Northwest France.

Our GPS tagged birds, along with an additional 48 non-tagged controls, were all fitted with yellow darvic rings with a black alpha-numeric code (number/letter:W e.g. 5A:W) in 2014. The colour ring is on the left leg and a BTO metal ring on the right. During the breeding season you can watch the movements of the tagged birds in near-real time at: http://www.uva-bits.nl/project/seabirds-windfarm-interactions-skokholm/

The darvic rings have yielded a fantastic number of field resightings; the 73 ringed birds have produced 90 separate resightings of 23 different individuals (including eight birds with GPS trackers). The following table summarises resightings received of non-GPS tagged birds since a similar table was published in the 2014 Seabird Report. There is already some evidence to suggest that Skokholm birds return to the same wintering areas, with records of birds at the same sites in northwest France and central Spain in consecutive winters; such wintering site fidelity has been found in birds from the other British Trust for Ornithology tracking sites (Ross-Smith, pers. comm.).

Darvic Ring Location Country Date 6U:W GR98226 Malaga Harbour Spain 22/02/15 6U:W GR98226 Mira Beach, Coimbra Portugal 01/10/15 7X:W GR98245 Matosinhos Beach, Porto Portugal 01/09/15 8H:W GR98250 Malaga Harbour Spain 01/01/15, 03/01/15

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8T:W GR98257 Figueira da Foz Portugal 06/11/15 9C:W GR98262 Colmenar Viejo Landfill, Madrid Spain 07/02/15, 16/08/15, 05/09/15 9H:W GR98264 Matosinhos Beach, Porto Portugal 28/08/15, 18/09/15, 16/10/15 9J:W GR98265 Barbate Harbour Spain 14/02/15, 15/02/15 9T:W GR98272 Sesimbra, Lisbon Portugal 13/12/14 9X:W GR98275 Eirol Landfill Portugal 02/12/14, 03/12/14 9Y:W GR98276 Portimao Harbour, Faro Portugal 15/01/15, 12/02/15, 20/02/15

Larus hybrid Larus fuscus x Larus argentatus (?) Scarce Breeder

An apparent hybrid was again holding territory with a Lesser Black-backed Gull above South Haven, the same site as occupied in 2013 and 2014 (see photograph below). As in 2014, the pair was regularly seen together during the course of the season but they were not seen with a nest, eggs or young. What was thought to be a different hybrid was on the Neck on 31st July, although this bird was not seemingly on territory. Whether the hybrid birds are remnants of cross-fostering experiments (500 Herring Gull and 400 Lesser Black-backed Gull chicks were raised by adults of the ‘wrong’ species between 1963 and 1966 with the result that they frequently paired with the species of the adopting parents) or whether they are the result of natural interbreeding, is unclear.

Herring Gull Larus argentatus Gwylan y Penwaig Common Breeder abundant breeder in the 1970s 23 trapped (including 2 pulli), 5 retrapped 1936-1976: 13,164 trapped, 2013-2014: 34 trapped, 5 retrapped

Numbers fluctuated in March, with birds typically feeding away from Skokholm but returning to roost on the Neck. Peak counts of 277 on the 28th, 444 on the 29th, 297 on the 30th and 349 on the 31st were similar to the previous two seasons, although the maximum was slightly up on the 418 of 8th March 2013 and the 364 of 29th March 2014. The number of birds logged was more consistent during April with over 200 on 16 dates (15 dates in 2014) and highs of 316 on the 5th and 326 on the 22nd (280 on the 30th in 2014). Although three birds were apparently incubating on the 15th, an inspection the following day found that all three nests were empty. It was not until the 25th that the

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first eggs were seen, with one nest containing two eggs and three further nests containing a single egg; the first egg was logged on 14th April in 2014 and 18th April 2013. The whole Island count took place on the 19th, 20th and 21st May when 289 active nests were located. This was a 3.7% drop on the 300 active nests found in 2014 but was 4% up on the 2006-2015 mean (292.0 ±sd 30.04) and the second highest count since 2010. The number of breeding pairs has apparently stabilised close to that seen in the 1930s, prior to the huge peak in numbers recorded in the 1970s (the 1928-1937 mean was 269.70 ±sd 17.47). May counts in 2014 were occasionally bolstered by large flocks feeding offshore, however these were not witnessed until the autumn in 2015.

The number of breeding pairs 1928-2015 (where data exists). The 1970s peak was attributed to the exploitation of local fish waste and the decline to botulism (Thompson, 2007). 1500

1300

1100

900

700

500

300

100

1973 1928 1931 1934 1937 1940 1943 1946 1949 1952 1955 1958 1961 1964 1967 1970 1976 1979 1982 1985 1988 1991 1994 1997 2000 2003 2006 2009 2012 2015

Although a youngster managed to glide a short distance on 1st July, fledglings were not seen in flight until the 10th (2nd July in 2014 and 7th July in 2013). July checks of the Neck productivity plot, where 140 pairs had established nests (146 in 2014), located a maximum of 93 fledglings on a single visit, along with five smaller chicks which may have gone on to fledge. The minimum productivity estimate of 0.66 fledged young per pair is 5.7% down on 2014, 9.6% down on the 2006-2015 mean (0.73 ±se 0.06) and is the lowest estimate since 2007. However Herring Gull productivity remains consistently higher than that of the closely related Lesser Black-backed Gull, circumstantial evidence suggesting that this may be due to differing feeding habits. Additionally Great Black-backed Gulls apparently target the coastal nesting Herring Gulls less frequently than they do the inland gull colonies. It would seem that the current level of productivity is sufficient to sustain a stable breeding population at this time.

The number of breeding pairs and productivity estimates (average number of fledglings per sample pair) 2004-2015. 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 287 255 265 320 287 353 312 257 274 263 300 289 0.18 0.57 0.47 0.61 - - 0.82 0.67 1.15 0.72 0.70 0.66

Numbers fluctuated significantly in August following the mass departure of both adults and fledglings; there were lows of 20 on the 20th and 26 on the 22nd but highs of 198 on the 28th and 240 on the 30th when birds returned to the Island to feed on swarming ants. As in the previous two seasons, few Herring Gulls visited Skokholm in September with between nine and 68 birds logged on each date except for on the 25th and 26th when feeding birds in Broad Sound bolstered the counts to 117 and 190 respectively. Despite a similar level of seawatching effort, October totals were considerably higher than in the previous two seasons due to an increase in the number of birds feeding with the Broad Sound gull flock; there were highs of 150 on the 10th, 152 on the 25th, 171 on

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the 30th and 136 on the 31st. Counts increased again in November with more birds joining the large feeding flock of smaller gulls which forms in Broad Sound on calmer days; there were highs of 335 on the 10th, 347 on the 11th, 383 on the 12th and 334 on the 22nd, counts considerably up on the 2014 November maximum of 267 and the 2013 peak of 220. Additionally there was a count of 585 birds, almost all adults, which roosted on an exceptionally calm sea in South Haven on the evening of 21st November.

Great Black-backed Gull Larus marinus Gwylan Gefnddu Fwyaf Fairly Common Breeder and Common Visitor 54 trapped (including 52 pulli), 1 retrapped , 1 control 1936-1976: 219 trapped, 2013-2014: 133 trapped, 6 retrapped, 2 controls

This year saw spring totals at the Bog roost very similar to 2014, with a March high of 37 on the 31st and April highs of 63 on the 12th and 62 on the 13th; the sizable roost which formed at the Bog during the early part of the 2013 season and which peaked at 213 individuals on 3rd April was also much reduced in 2014 when there was a March high of 34 individuals on the 30th and an April high of 54 on the 20th. A whole Island count on 7th May located 80 active nests and there were a further three attempts located over the following 13 days. A total of 83 breeding pairs was the third highest total yet recorded on Skokholm, just one less than the record totals of 2014 and 2011. Two pairs which had nested on the wall to Little Bay Point in 2014 relocated this year, occupying sites further from the path network; although this perhaps supports the theory that disturbance may limit the breeding population (a theory proposed during the period of Island closure when numbers increased dramatically), the high totals logged in the last two years have occurred during a period with high guest numbers.

The Great Black-backed Gulls are spectacular apex predators and an exciting component of the Skokholm seabird assemblage, however it is important that we monitor the impact of these high breeding numbers on the Manx Shearwater population. With this in mind dead Manx Shearwaters were counted for a second consecutive year, the vast majority of which had been predated by Great Black-backed Gulls; a total of 4123 corpses, comprising 2702 adults, 378 chicks and 1043 fledglings were marked (4272 corpses, comprising 2931 adults, 269 chicks and 1072 fledglings in 2014). Although a relatively small proportion of the Skokholm population, it seems likely that a continued increase in the Great Black-backed Gull population will increase their impact on the Manx

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Shearwaters (see Manx Shearwater for further details). Although evidence collected at the nests suggested that the gulls are exploiting natural food sources, primarily seabirds and rabbits, up to ten individuals were seen to be collecting discards from a lobster potting vessel on 4th April and two were feeding from a floating cow on 9th August; an important step to understanding the Great Black- backed Gull population on Skokholm will be to discover if such anthropogenic food sources are regularly exploited, particularly during the non-breeding period.

The number of Great Black-backed Gull breeding pairs 1928-2015 (where data exists). Control of numbers started in 1949 (destruction of both nests and adults) and stopped in 1985. 90 80 70 60 50 40 30 20 10

0

2015 1931 1934 1937 1940 1943 1946 1949 1952 1955 1958 1961 1964 1967 1970 1973 1976 1979 1982 1985 1988 1991 1994 1997 2000 2003 2006 2009 2012 1928

The first two eggs observed this year were in a nest to the north of Orchid Bog on 19th April; the first egg of 2014 (a single) was found on 10th April and the first record of 2013 (two full clutches) was on the 25th. Of 35 monitored nests, nine pairs failed at the egg incubation or small chick stage, four pairs fledged a singleton, 12 pairs fledged two and ten pairs fledged three. There were thus 58 fledglings and a productivity figure of 1.66 fledged young per monitored pair. Productivity was 78.5% up on 2014, 52.3% up on the 1989-2004 mean of 1.09 and 45.6% up on the 2006-2015 mean (1.14 ±se 0.12). Despite the increase in the breeding population, productivity has been well above average in two of the last three years.

Productivity estimates 2005-2014 (average number of fledglings per sample pair). 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 0.76 1.07 1.02 1.02 - 0.71 0.89 - 1.80 0.93 1.66

In an effort to further understand observed population growth, a Great Black-backed Gull colour ringing project was begun in 2014. Over the coming years it will hopefully shed new light on adult survival and juvenile recruitment. Of 23 adult birds ringed in 2014, 19 (82.6%) attempted to breed in the same territories this year and four were not seen; as all of the breeding adults present on Skokholm this breeding season were checked for rings, it seems likely that this is a very good approximation of return rate, although whether it reflects adult survival will require further study as some extant birds may not have returned. This year there were 54 red darvic rings with white lettering fitted, two to adult birds of at least four years of age and 52 to fledging sized chicks. One of the fledglings was subsequently found dead on the Island. Over the last two years 27 different birds have been resighted away from Skokholm (from a total of 122 ringed birds). There have been three adult birds resighted in the winter (one in Pembrokeshire and two in Cornwall) and 24 young birds resighted (the majority in Cornwall). Although records will be somewhat biased by a preponderance of birders at the main roost sites in Cornwall, it seems likely that these records reflect a genuine southerly bias to the movements of young Skokholm Great Black-backed Gulls. The only young bird

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we know to have returned north is W:055 which, having first been sighted on the Nevern Estuary, Newport on 19th October 2014, was seen at Chynhalls Point, Cornwall on 19th February 2015 before returning to the Nevern on the 1st, 9th and 29th October 2015. Of the 44 fledglings ringed in 2014, one (W:056) was resighted on Skokholm this year with a single visit logged on 5th April. All of the records below are field sightings unless stated otherwise.

Darvic Ring Location County Age Date W:028 HT94873 Gann Estuary Pembrokeshire Adult 21/08/15 W:031 HT94876 Camel Estuary Cornwall Adult 24/01/15 W:034 HT94895 The Lizard* Cornwall First Winter 03/03/15 W:034 HT94895 Gwithian* Cornwall First Winter 28/04/15 W:037 HT94899 Hayle Estuary Cornwall First Winter 24/02/15 W:039 HT94878 Gwithian Cornwall First Winter 11/03/15 W:040 HT94900 Haverfordwest (DEAD) Pembrokeshire First Winter 21/08/14 W:043 HT94903 Coverack Cornwall First Winter 19/02/15 W:045 HT94905 The Lizard* Cornwall First Winter 03/03/15 W:045 HT94905 Gwithian* Cornwall First Winter 28/04/15 W:047 HT94908 Trevose Head Cornwall First Winter 19/03/15 W:047 HT94908 Looe Island Cornwall First Winter 29/03/15 W:047 HT94908 Looe Island Cornwall Second Winter 09/09/15 W:047 HT94908 Axe Estuary Devon Second Winter 10/11/15 W:049 HT94910 The Lizard Cornwall First Winter 09/02/15 W:055 HT94917 Chynhalls Point Cornwall First Winter 19/02/15 W:055 HT94917 Nevern Estuary Pembrokeshire Second Winter 01/10/15 W:060 HT94921 Hayle Estuary Cornwall First Winter 31/01/15 W:061 HT94922 Tourlaville Normandy, FRANCE Second Winter 08/11/15 W:063 HT94924 Wadebridge Cornwall First Winter 29/03/15 W:063 HT94924 Camel Estuary Cornwall Second Winter 16/09/15 W:069 HT94929 Mullion Island (DEAD) Cornwall First Summer 07/05/15 W:070 HT94882 Nevern Estuary Pembrokeshire First Winter 17/03/15 W:073 HT94930 Nevern Estuary Pembrokeshire First Winter 05/01/15 W:081 HT94938 Gann Estuary Pembrokeshire First Winter 13/12/15 W:095 HT94958 Grassholm Pembrokeshire Juvenile 09/08/15 W:100 HT94963 The Lizard Cornwall First Winter 15/09/15 W:107 HT94970 Ouessant Island Brittany, FRANCE First Winter 17/10/15 W:124 HT94955 Gann Estuary Pembrokeshire Juvenile 21/08/15 W:126 HT94982 Trevose Head Cornwall First Winter 26/10/15 *W:034 and W:045 were together at the Lizard on 3rd March and together at Gwithian on 28th April.

A roost of up to 82 birds, but more typically less than 40, regularly formed in the Bog during the breeding season; the majority of birds were in full adult plumage, although there were five first-

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summers on 2nd May and there were occasional records of subadults joining the roost. There were peak roost counts in May of 54 on the 5th and 16th, 82 on the 27th and 55 on the 29th and in June of 43 on the 2nd, 42 on the 6th, 38 on the 11th and 17th, 39 on the 21st and 38 on the 24th. The first fledglings were recorded away from their natal area on 7th July, however, with the exception of a roost of 46 on 27th July, it was not until mid-August that larger communal roosts formed. North Plain and the area to the north of the Sugarloaf again proved the most popular post-breeding roost sites, with peak counts of 44 on 24th August, 96 on the 25th, 91 on the 26th (49 of which were at the Sugarloaf), 88 on the 27th (19 at the Sugarloaf), 118 on the 28th (37 at the Sugarloaf) and 53 on the 31st. There were August records of Skokholm ringed fledglings on Grassholm on the 9th and at the nearby Gann Estuary on the 21st, whilst the first youngster to be recorded away from Pembrokeshire was on the Lizard, Cornwall by 15th September. In September there were peak counts of 198 on the 5th (including 124 in the North Plain roost), 181 on the 13th (115 North Plain), 234 on the 15th (108 North Plain) and 249 on the 22nd (179 North Plain); although well below the September 2013 peak of 355, the 2015 counts were up on the September 2014 maximum of 52. There were early October highs of 166 on the 5th (136 North Plain) and 130 on the 6th (108 North Plain), although there were only between three and 32 logged each day between the 13th and the end of the month; the 2013 peak of 149 was logged on two dates and the 2014 high was 107. November counts were again well down on the peaks of 270 and 243 logged in 2013, but slightly up on those logged in 2014; there were highs of 54 on the 9th, 71 on the 13th and 44 on the 25th, although there were only single figure counts on 11 dates and lows of two on the 2nd and 5th.

The movements of Skokholm ringed Great Black-backed Gulls 2014-2015.

One adult bird One second-winter bird One first-winter bird

Two first-winter birds

Three first-winter birds

Five first-winter birds

Google Imagery © 2014 TerraMetrics

Literature Cited

Betts, M. (1992) Birds of Skokholm. Dyfed Wildlife Trust Birkhead, T.R. (1984) Distribution of the bridled form of the Common Guillemot Uria aalge in the North Atlantic. Journal of Zoology 202 (2): 165-176

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Brooke, M. de L. (1990) The Manx Shearwater. Poyser Brown, R. and Eagle, G. (2013) Skokholm seabird report 2013. Online report for the Wildlife Trust of South and West Wales Brown, R. and Eagle, G. (2014) Skokholm seabird report 2014. Online report for the Wildlife Trust of South and West Wales Ferguson-Lees, J., Castell, R. and Leech, D. (2011) A Field Guide To Monitoring Nests. BTO Gillham, J. and Yates, L. (2012) Skokholm Island Annual Report 2012. Unpublished report for the Wildlife Trust of South and West Wales Gynn, E. (1984) Dead shearwaters on Skokholm. Bulletin of the Friends of Skomer and Skokholm 7:10-11 Harris, M., Heubeck, M., Shaw, D. and Okill, D. (2006) Dramatic changes in the return date of Guillemots Uria aalge to colonies in Shetland, 1962-2005. Bird Study 53: 247-252 Harris, M., Heubeck, M., Newell, M. and Wanless, S. (2015) The need for year-specific correction factors (k values) when converting counts of individual Common Guillemots Uria aalge to breeding pairs. Bird Study 62 (2): 276-279 Humphreys, E.M., Wanless, S. and Bryant, D.M. (2007) Elevated metabolic costs while resting on water in a surface feeder: the Black-legged Kittiwake Rissa tridactyla. Ibis 149: 106-111 Perrins, C.M. (2014) Factors affecting survival of fledgling Manx Shearwaters Puffinus puffinus. Seabird 27: 62-71 Smith, S., Thompson, G.V.F. and Perrins, C.M. (2001) A census of the Manx Shearwater Puffinus puffinus on Skomer, Skokholm and Middleholm, west Wales. Bird Study 48: 330-340 Sutcliffe, S.J. and Vaughan, D. (2011) Storm Petrel monitoring on Skokholm. Unpublished report for the Wildlife Trust of South and West Wales Thompson, G.V.F. (2007) The natural history of Skokholm Island. Trafford Publishing

Manx Shearwater with water droplets, Manx Shearwater in flight at sea, Manx Shearwaters in flight at night and Storm Petrels in flight at night (x2) © Bart Vercruysse Puffin in flight with fish © Kevin Maskell Herring Gull with Puffin, Puffin inspecting corpse and Razorbill with fish © Richard Coles ([email protected]) All other photographs © Richard Brown and Giselle Eagle

Report compiled by Richard Brown and Giselle Eagle

This work was funded in part by Natural Resources Wales

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