GANNET COLONIES OF SHETLAND.*

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1 (162) GANNET COLONIES OF SHETLAND.* JAMES FISHER, MALCOLM STEWART AND L. S. V. VENABLES. {Plate 5.) IN Shetland there are two colonies of Gannets (Sula bassana), one on the east cliffs of the island of Noss and the other on the stacks and cliffs of Hermaness, North Unst. The Noss has been visited by L.S.V. V. in all breeding seasons between 1934 and J.F. visited it in 1937 and 1938, and M.S. in All three writers were at Hermaness, Unst, on various dates in June and July, Noss. J.F. and L.S.V.V. [2] have described the previous counts and estimates of the Noss. They are as follows : or or ,518 pairs (count) Details of the 1937 estimate and 1938 count can be found in [2]. In all cases the number of breeding pairs is recorded. The particular cliffs colonized are the north and south faces of the Noup and Rumble Wick. HERMANESS. All the writers visited this gannetry in June and July, 1938, and it is definite that Gannets only nest in three main groups near Hermaness, which can be divided as under: 1. Vesta Skerry (In Muckle Flugga group) Humla Stack 2. Hermaness Hill Burra Stack Humla Houl (a) Neapna Stack 3. Neap *Gannet Population Studies, No pair 4 pairs 3 young reared 5 pairs 10 pairs 200 pairs (estimate) 800 pairs (estimate) 913 pairs (estimate) jjjjl [The Neap (e) )

VOL. XXXII] SHETLAND GANNET COLONIES. 163 Vesta Skerry, seen from N.W. Herma Ness in background. [Photographed by James Fisher.) Direct counts were made from land and sea as under (Table i). TABLE i.

2 VOL. XXXII] SHETLAND GANNET COLONIES. 163 Vesta Skerry, seen from N.W. Herma Ness in background. [Photographed by James Fisher.) Direct counts were made from land and sea as under (Table i). TABLE i. COUNTS OF THE NUMBER OF BREEDING PAIRS OF GANNETS IN THE HERMANESS COLONIES IN JF LSVV MS MS MS MS MS Taken 26th 26th 7-gth 13th 15th 18th 20th as June June July July July July July Vesta E. 460 l Skerry W ) Humla Sea Stack Land 31 3i 29 i Burra Sea Stack Land Humla Sea Houl Land J 4 8 l6 4 Neapna Sea Stack Land A. Neap Sea j, ~ 5 45 l 2y4 B. Land y J I J Neap Sea C. Land Neap D E Total 2,045

3 164 BRITISH BIRDS. [VOL. XXXII. The written history of this gannetry is somewhat involved ; it is summarized in Table 2. Many errors must be due to recorders mistaking the names of the stacks and cliffs. Those used by the authors are from the Ordnance Survey six-inch maps of Zetland, second edition, The name " Humla Houl " was not recorded on these maps, but is used by the inhabitants of Unst and by Macpherson [5]. Muckle, Flugga \ Group Vesta Skerry Hermaness, Hill \ Group Burra Stack Total No. of Pairs Almost certainly erroneous. fprobably Burra Stack is meant. TABLE 2. THE HISTORY OF THE HERMANESS GANNET COLONIES ! /Muckle Flugga Rumblings V '"Humla Stack Humla Houl /Neapna Stack Neap, Group Neap 1917 (6)* (4)? (6)* 9 (4}, 100 on S. side, N. side not seen (7) (6)t. small seaward side (7)t J 1,000 (4) (4)t no ; never occupied no ; never occupied W 1? 200 (1) 200? (1) 200 "? W 600? 200 /200 I200 /200 J ]200 1,000 (1) i

VOL. XXXII.] SHETLAND GANNET COLONIES. 165 Macpherson [5] suspected the possibility of the extending to the Greing on Hermaness and to the Saxavord cliffs on the east side of Burra Firth.

4 VOL. XXXII.] SHETLAND GANNET COLONIES. 165 Macpherson [5] suspected the possibility of the extending to the Greing on Hermaness and to the Saxavord cliffs on the east side of Burra Firth. On the latter were found no traces of either breeders or non-breeders. On the other hand the Greing was seen on one occasion to afford a resting place for birds in immature plumage, though there The Neap from Saito. "A" = Neapna Stack. " B" to " E " = The Neap (Sensu stricto). (Photographed by Malcolm Stewart.) were definitely none breeding on it. In the same way a large flock of non-breeders or non-incubators used the Rumblings next to Vesta Skerry, and 350 were counted on one occasion. There are certain cliffs at Clibberswick between Norwick and Haroldswick, on the east coast of Unst, and which are marked on the map as " Sula ". The name, or word, " Sula ", of course, suggests the Gannet; there are, however, no Gannets on these cliffs, and indeed they would appear unsuitable for a nesting-site. Inquiries were made locally in Unst, but no one could state the meaning of the word " Sula " as applicable to the cliffs.

5 166 BRITISH BIRDS. [VOL. XXXII. COLONIZATION. It is not known how many pairs were at the probable start of the in 1917, but it can be easily imagined that the total of 2,045 breeding pairs in 1938 must have been attained by regular colonization from outside. If all Gannets were immortal and perpetually fertile, but did not colonize, then using the reasoning set out in [2] it can be calculated that the population could have been derived from a stock of 18 or 19 pairs in Burra Stack from W.N.W. {Photographed by James Fisher.) COMPARISON OF THE TWO COLONIES. Of the 20 colonies in the world (Funk Island [3] has now been added to those recorded in [1]), all are on small islands, with the exception of Anticosti Island, Cape St. Mary and Hermaness. Though Noss is a small island, the channel which separates it from the large island of Bressay is only 200 yards wide, so it is possible that this should be also placed in the large island or " mainland " category. With a few exceptions the Gannets on Hermaness nest on smallish detached stacks of a maximum height and approximate depth of 150 feet. On Noss, however, the Gannets nest in the neighbourhood of the sheer 592 foot Noup, and the cliffs they have chosen have a minimum height of about 250 feet.

6 VOL. XXXII.] SHETLAND GANNET COLONIES. 167 MUCKLE FLUGG^ tl6hthcusi RUMBLINGS VESTA SKERRY ' SKETCH MAP OF HERMANESS GANNET COLONIES, UNST, SHETLAND. I CO Z =J Based upon the Ordnance Survey Map with the sanction of the Controller of H.M. Stationery Office. LU o O -z. < z <

7 168 BRITISH BIRDS. [VOL. XXXII. The Muckle Flugga group, seen from S.W. LEFT Muckle Flugga, showing lighthouse. LEFT CENTRE FOREGROUND Vesta Skerry. RIGHT The Rumblings. (Photographed by James Fisher.) Neapna Stack from top of " D ". (Photographed by Malcolm Stewart.)

8 VOL. xxxn.] SHETLAND GANNET COLONIES. 169 It is noticeable that non-breeders and birds in immature plumage are almost unknown on Noss, whereas at Hermaness they are to be seen constantly and in considerable numbers. Another point of difference is the relationship of the Gannets with the bonxies or Great Skuas {Stercorarius skua skua). At both places there are colonies of the latter, but it should be remembered that the bonxies colonized these places before the arrival of the Gannets. At Hermaness it is a common spectacle to see a bonxie chasing a Gannet and attempting to make it disgorge, in fact, very often several of these chases can be seen taking place at the same time. On the other hand at Noss one can watch (for long periods of time) the Gannets returning with food, without seeing one of them attacked by a bonxie. The writers wish to record their gratitude to Mr. G. T. Kay, of Lerwick, who so kindly took them to these colonies in his boat the Soldian; and to Laurence Bruce and James Jamieson, the R.S.P.B. watchers on Hermaness and Noss respectively. REFERENCES. [i] EDWARDS, V. C. WYNNE-, LOCKLEY, R. M., and SALMON, H. M- (1936). Brit. Birds 29 : " The Distribution and Numbers of Breeding Gannets (Sula bassana.)." [2] FISHBR, J., and VENABLES, L. S. V. (1938). /, Anim. Ecol. 7 : (in press, Nov. issue). " Gannets (Sula bassana) on Noss, Shetland, with an analysis of the rate of increase of this species." [3] GILWARD, E. T. (1937). -Auk 54 : 379- Sl - " The Gannets of Funk Island." [4] GRIFFITH, A. F. (1929). Bull. Brit. Orn. CI. 49 : [5] MACPHERSON, A. H. (1933). Scot. Nat : IlS - " Gannets in Shetland." [6] RITCHIE, J. (1929). Scot. Nat : " The Gannets of the Bass Rock. Estimated numbers and a count." [7] MEADE-WALDO, E. G. B. (1920). Brit. Birds 14 : "A New Nesting-place of the Gannet."

9 British Birds, Vol. XXXII., PI. 5. vesta Skerry Muckle Flugga Burra Stack Humla Houl Humla Stack Greing Panorama of the Hermaness Hill and Muckle Flugga Groups. (Photographed by Malcolm Stewart.)

Gannet surveys in north-west Scotland in 2013

Plate 120. St Kilda with (left to right) Stac an Armin, Boreray and Stac Li, 19 June 2013. SNH/S. Murray Gannet surveys in north-west Scotland in 2013 S. Murray, S. Wanless & M.P. Harris A photographic