Collins New Naturalist Library. H. Hewer R.

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СКАЧАТЬ the Pentlands) another 250–300 are born. The research work and a local intensification of sealing has recently reduced the population a little and disturbance in one breeding season has been reflected by a change of site or a redistribution of numbers in the next.

      Many other skerries, such as Auskerry, Taing Skerry, Wyre Skerry, Eynhallow, Boray Holm, Holm of Birsay, Damsay, the Barrel of Butter and others are used as haul-out sites during the non-breeding period, some of the breeding islands such as Rusk Holm, Holms of Spurness and Little Greenholm are also used in the early months of the year. It is, however, very noticeable that non-breeding haul-outs are never seen on the major breeding rookeries. This differentiation of site use is particularly well shown on Rusk Holm where the two southern skerries are used as reservoir haul-outs during the breeding season, the rookery is on the eastern pebble beach and north-eastern rocks, while the moulting haul-outs are either on the north-western rocks or on the south or south-eastern rocks according to wind and tide.

      The numbers in Shetland are much fewer. This must be attributed as much to the rock-bound nature of the coast-line as to the scarcity of small uninhabited islands. In the southern part Lady Holm, Horse Holm and the geos or narrow beaches under Fitful Head provide small rookeries. Only in the north does the lie of the islands provide any lee so that small rookeries are found around Yell and Fetlar. The beaches under Ronas Hill are important breeding sites. In total there are probably only 200–300 pups each year.

      In the non-breeding season the major haul-outs in the south and west are on Horse Holm, Lady Holm, around Fitful Head and on the Ve Skerries, west of Papa Stour. Small though these last are they sometimes hold up to 2,000 seals not all of which can be considered as Shetland grey seals in the sense that in the breeding season they will be found on the Shetland rookeries. Fair Isle, halfway between Orkney and Shetland, also has haul-outs and as a number of young seals marked in Orkney have been found in Shetland there is little doubt that the adults move freely between the two groups of islands. The picture here too is somewhat complicated by the presence of common seals and there is no doubt that much more is to be learnt about their distribution here, particularly in the northern islands.

      In Orkney and Shetland there has persisted a tradition of sealing which has never been so strong in the Hebrides, possibly by reason of the Norse connections. The grey seal population here, therefore, appears to be fairly stable, fluctuating largely as a result of variations in sealing effort dependent, in turn, on the market price of seal-skins.

      NORTH SEA GROUP

      There is little difficulty in deciding that the centre of this group is the Farne Islands (Pl. 5). The North Sea is peculiarly free of islands and it may as well be stated straight away that only on the Island of May in the Firth of Forth and on Scroby Sands off Great Yarmouth are there any breeding rookeries other than on the Outer Farnes. Elsewhere there is evidence of their fishing inshore along the east as far south as the Wash, and the coast of Holland, and as far north as the Moray Firth. Fishing haul-outs have been recorded from the Abertay Sands to the Wash, but there is always a haul-out on the outermost islands of the Outer Farnes. At certain times of the year, notably the spring, they consist of very large numbers indeed. The population has been rising steadily in recent years. Annual counts of pup production have been made with considerable accuracy over the past fifteen years or so and an annual increase of about 7% has been calculated. Undoubtedly at the turn of the century the population was at a very low ebb. The islands at present involved as rookeries are the North and South Walmses, Staple and Brownsman, but in the more distant past others were used as rookery sites such as the Wide Opens and other islands of the Inner Farnes. At times of the year, other than the breeding, haul-outs are found on the Longstone and Longstone End, the Harcars and on other skerries of the Outer Farnes. All of these islands are low with at least one or two shelving rock beaches so that access is easy and sheltered within the archipelago. The interiors of the islands are used as well as the ‘beaches’ for rookery sites, but usually only after the more shoreward zones have become congested.

      At the time of writing the number of pups produced annually had reached 2,011 (1971) making the Farne Islands group the third largest known in the British Isles with an estimated total population of almost 6,500–7,000.

      Before going into the details of the life history of the grey seal, it is necessary to give a brief description of the yearly cycle of both adult males and females. Until recently it was really quite unknown. Even worse, statements appeared in the literature which cannot have been founded on observation because they were so wildly wrong. Until the early 1950’s this species had only been studied during the breeding season. It is not difficult to find the reasons for this. During the late autumn and winter months the weather makes visits to the islands a very chancy affair and few people feel inclined to camp on these isolated spots during this time of year. Yet these are the only ways in which information can be gathered. During the summer months the weather is generally good but on the other hand very few seals will be seen. For the spring however, there is no excuse and it is a very important season indeed. Dr K. M. Backhouse and myself started visiting the Ramsey Island sites in 1952 and soon every month except December and July had been covered. Later all months in Orkney had been covered by Mr E. A. Smith and in the Farnes by Dr J. C. Coulson and Mrs Hickling. The work of Craggs and Ellison throughout the year on West Hoyle Bank has already been referred to. (Oddly enough it was undertaken quite independently of the other work in Pembrokeshire, Orkney and Farnes on which there was considerable interchange of knowledge and information. An example of this interchange will be given below when dealing with the annual moult.)

      The best time to start describing the annual cycle is during the summer months of June, July and August. This is a very active feeding period for both bulls and cows. The bulls have to put on sufficient blubber to sustain them during their period of starvation, while they are maintaining territory. The cows also have to put on blubber to provide the fat for the rich milk suckled by the pups, but in addition, must eat sufficient to permit the foetus within to grow. (During the summer the foetus may increase by more than a pound a week.) Towards the end of August there is a tendency for both bulls and cows to move towards their breeding areas. This has been shown by J. Morton Boyd by the ingenious analysis of observations made at a number of points along the coastline of north-west Scotland. In the south-western group this drift is probably a little earlier, but newly arrived cows have been seen by me in early September on Ramsey Island. It is difficult to be precise in an animal whose breeding period extends over at least 2 months. The most that can be done is to note when such a tendency is at its peak and therefore most conspicuous. Other individual seals will still be at sea feeding, others still may already have arrived at the breeding rookeries and have pupped.

      Bulls and cows must now be studied separately because the purpose of their assembling in the rookeries is quite different and consequently their behaviour and timing is different. Put very briefly and perhaps in an over simplified way, bulls assemble for mating, cows for pupping and only secondarily for mating.

      Bulls seem to predominate at the beginning of the breeding season on or near the rookeries. Here they appear to sort themselves into a dominance order, those having previously bred clearly taking precedence over the younger ones. Gradually they take up station on a territory which they defend against all comers (Pl. 7). Although they immediately approach an invading cow, their agonistic behaviour dies down as soon as they recognise her sex. Invasion by new and younger bulls (Pl. 6) continues for a considerable time and for at least a fortnight or so defence is the dominant activity of each bull holding territory.

      Meanwhile cows begin to arrive at the rookeries (Pl. 7) and shortly give birth to their pups. Suckling commences within the hour and is repeated several times a day for at least a fortnight, sometimes for nearly three weeks. During this period the cows resent any approaches by the bull, who is СКАЧАТЬ