Collins New Naturalist Library

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 (#ulink_d6c6e2eb-ab7f-5299-b84b-7d59372c698e)). 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 (#ulink_d48cae9d-2ce7-57df-bd3e-dcf2a1cb6a70)) 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 (#ulink_d6c6e2eb-ab7f-5299-b84b-7d59372c698e)) 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 repelled by hooting and rapid waving of the fore flippers (‘flippering’). Eventually, some time in the third week after giving birth, the cow accepts the bull in mating. Mating is often repeated several times at intervals. The cows desert their pups and leave the rookeries. Whether they go immediately to sea or remain in nearby waters is not yet certain, although I am inclined to believe the former is more likely.

The deserted pups moult their first or ‘puppy’ coat of white hair and appear in their ‘moulter’ coat which is similar to the adult pelage. In a healthy pup this process takes about a week; the fourth week of their life. When moulted the pups may, as in the south-west, immediately leave their natal beach, or as in the north and north-west remain on land and in fact move farther inland. Hunger will however eventually drive them to sea within a week or two.

The bulls remain on station for five to six weeks before becoming exhausted. They then move away from the rookeries to sea and recommence feeding to restore the blubber they have used during their enforced fast.

While this is the time-table of individual cows and bulls, it must be remembered that the time-table of the rookery is more extended. Thus a fortnight after the first pups have been born matings will begin, but this will probably be before the peak of the pupping. Consequently while the peaks of the various processes, pupping, mating, moulting, desertion by cows and leaving by bulls will be separated by periods corresponding to the normal time-table of individuals, this central period will be preceded by two or three weeks when arrivals of bulls and cows and some pupping are the only phenomena and will be followed by several weeks in which mating and desertions will predominate. The overall period will be about

months.

Now follows a period about which not so much is known. The nearby haul-out sites are used but not to a great extent. Probably the answer is that both bulls and cows are feeding as much as possible to replace their lost blubber, to fit themselves for the rigours of the winter. One of the most remarkable facts of this period, which covers about

months, is that among the cows found on the haul-outs, non-pregnant ones predominate. A high proportion of these non-pregnant cows are comparatively young and virgin or nulliparous. The differential behaviour of pregnant and non-pregnant cows is very remarkable, the more so because very little development of the embryo takes place for the first hundred days after conception (about

months). (See Chapter 4 (#litres_trial_promo).) Towards the end of this period most of the cows go into the annual moult.

I have not mentioned the actual dates through this breeding and post-breeding period because there are differences between the geographical groups and generalisation is therefore difficult. What makes precision even more difficult is that the full story is not known in detail for all of the groups. However, some attempt may be made to give an overall picture if we omit the Farne Islands group. In the south-western group the peak of pupping is probably in the first week in October, and by mid-November all the beaches are completely deserted. In the Hebrides and North Rona the dates are about 10–14 days later, although the much larger size of the rookeries results in more early and late puppings so that the season appears to be longer and a few adults may still be found in the breeding grounds in early December. In Orkney and Shetland a further 7–10 days should be allowed, so that mid-December would be a reasonable date to compare with mid-November in the south-west. January to March may be counted as the months of the cow moult, although few Orcadian cows will have begun in January and few, if any, Pembrokeshire ones will remain unmoulted in March.

For the Farne Islands group all these dates must be delayed by about a further month. There the first pups are in late October and the peak about 3–4 weeks later in November, pupping continuing actively well into December.

Our knowledge of the growth of the foetus is derived solely from northern material from Orkney. The mean date of the recommencement of the growth of the embryo is the middle of February. Thereafter the foetus grows apace in about 80% of the cows, the others are non-pregnant. So far as can be made out they continue to fish in the adjacent seas periodically coming ashore in fishing haul-outs for short periods at low tide. In the summer months the haul-outs must be both few and short because the numbers seen are very few indeed compared to those at other times of the year.

We have left the bulls at sea after the breeding season and it is not until mid-February that we have any evidence that large numbers come ashore. Their annual moult appears to be timed about two months after that of the cows. It was first observed in April in Pembrokeshire, but by then many were completely moulted and few remained unmoulted early in May. Dr Backhouse and myself, having found the comparatively large moulting haul-outs of bulls in Pembrokeshire, were able to direct attention to this in other groups, such as the Farne Islands, where the same phenomenon was then seen by other observers. These moulting haul-outs of the bulls are very remarkable and often number thousands at a time in the large northern groups. The bulls, like the cows, largely disappear in the summer months from all the inshore sites and we can only conclude that they too are feeding at sea to prepare themselves for the breeding season.

We can now turn to some of the distinguishing characteristics of this species, both in structure and habits.

It is always extremely difficult, if not impossible, to estimate the length or size of seals in the field since there is rarely, if ever, any standard for comparison. Measurements therefore, while of use on a carcase, cannot really be used by an observer in the field. Any deductions based on claims to be able to ‘age’ seals in the field must therefore be regarded as highly dubious and probably very misleading. The pup is born at a length of about 33 ins. and 32–33 lbs. Bull pups appear to be very slightly heavier, but the difference is not truly significant having regard to the numbers which have been weighed. In any case it could only amount to a few ounces. It is very difficult indeed to speak about moulters since by that time all the differences in nutrition have taken effect and weights can vary between 100 lbs. or more and little more than the birth weight, if the moulter has been starved and is likely soon to die. The growth in length is quite small so that few moulters reach 40 inches until well after they have left their natal beaches however great their weight. Some of these very heavy moulters (over 100 lbs.) are so bloated with blubber that they can hardly turn their heads and movements are quite lethargic. There is some evidence that pups which do not reach the weight of 90 lbs. before being deserted by their mothers and moulting, have little or no chance of surviving their first year of life. Certainly all those below 60 lbs. appear to die before the first six months is out and all the recorded weights of grey seals in their first year of life are about 90 lbs. or less. Further, yearlings which have been weighed on the Farne Islands appear to fall more or less within the limits shown by the largest moulters. In other words there is little, if any, increase in weight in the first year of life.

These conclusions appear to be confirmed by the known weights of older bulls and cows. 3–4 year old bulls only weigh 170–190 lbs. while the same age group of cows weigh 130–150 lbs.; 5–6 year old cows may reach 170–180 lbs. but records for bulls are very few, although they suggest that by that age they may attain 2 cwt. There are practically no weights of fully mature bulls or cows to justify generalisations. All that can be said is that probably the older well-established breeding cows are over 2 cwt. and the older territorial bulls probably top 3 cwt. or even reach 4 cwt. In any case the bulls vary much more than the cows and in both sexes changes in weight amounting to

cwt. are usual during the yearly cycle.

Much more data is available about lengths. Although little, if any, weight is acquired during the first year, the moulters grow considerably in length, an average of 55–60 ins. being normal at the end of the first year for both sexes. Thereafter some differences can be considered significant between the two sexes. The rate of growth is fairly steady until puberty at 5–6 years when cows will average about 6 ft. and bulls 6 ft. 6 ins. During the following 3 or 4 years the rate of growth of cows declines so that at 10 years of age they have attained their near maximum of 80–84 ins. (7 ft.). Some growth appears to continue throughout life but it is very small in the cows.

The years following puberty in the bulls account for the great difference between the older bulls and cows, for their rate of growth falls off much more slowly and is continued at the higher rate for a longer period. By 10 years of age the average is 90 ins. and 96 ins. is reached about 2 years later. Thus in round figures mature cows are about 7 ft. long and territorial bulls average about 8 ft. but may vary about 6 ins. more or less.

Turning now to the pelage we find very useful characters to distinguish bulls and cows in the field. These features are, in fact, visible in the pigmentation of the skin of the foetus at a comparatively early age, namely at 110–120 days of active gestation. Growth of the white pup hair coat however obscures this pigmentation by the 150th day of foetal growth. This puppy coat is uniformly unpigmented except occasionally in the region of the muzzle and top of the head. The hair is very long and creamy white on the newly born pup. The occurrence of the greyish areas around muzzle and crown has been interpreted as part of the moult which has taken place before birth and only resumed later at about 3 weeks of age. The excuse for this belief lies in the peculiar hormonal situation existing in the pup at birth, but examination of the hair from these areas shows that the pigment is confined to the tops of the hair and that the hairs themselves are quite unlike those of the later moulter coat. No explanation of these greyish areas is yet available, and their occurrence is very odd. Some groups, notably Pembrokeshire, show a much higher incidence than others, such as the Farnes. Further, these areas are the first to show any hair in the foetus and the time of their eruption makes it clear that the tops must have been formed in the follicles before the appearance of any general pigmentation in the skin.

The pup may begin to moult as early as the 10th day, but this is most unusual and it is generally the 18th day before the first signs appear on the fore and hind flippers and on the head. If the pup belongs to a group such as the Pembrokeshire where entering the sea is a common occurrence, much of the moulting hair is washed off and, as the puppy coat becomes thinner, the pattern of the moulter coat shows through. Even here, however, many of the pups do not enter the sea during the moult and in the northern groups, of course, this is the usual pattern of behaviour. Under these conditions the puppy coat is rubbed off in patches and often the moulter can be found lying on a carpet of its old hair.

This moulter coat is to all intents and purposes the same as all the subsequent coats, heavily pigmented on the back and sides at least and marked by even darker spots and blotches. It is in the abundance and distribution of the darker spots that the difference between bulls and cows can be seen. In cows the lighter pattern consists of a medium grey back shading to a lighter belly, the darker spots are comparatively few and only rarely run together. In the bulls the darker pattern is so extensive that the lighter one is seen only as small triangular patches between the dark spots and blotches which have run together over most of the body.

There is, however, considerable variation in both sexes. In the cows the pale underside may be any colour from pale cream to tawny yellow and the upperside may vary from grey or blue-grey to brown. Some cows may have very considerable blotching, but never to the extent shown in the bulls. In bulls the chief variation is in the overall tone of the darker pattern which may be dark brown to black in colour. A number of older bulls too show a markedly lighter head and sometimes the blotches unite so much as to give the impression of uniform black or dark brown.

These remarks of course apply to the new coat which is grown each year. As the time of moult approaches the whole pelage becomes duller, browner and more uniform in appearance due to the splitting of the hairs so that it is only in the wet pelt that the patterns can be distinguished. It should always be borne in mind when observing grey seals on shore that the appearance of the pelage alters considerably as it dries and that the change is more marked as the moulting season approaches.

The disparate growth of the bulls and cows is well seen in the skull and reflected in their profiles. The skull of the grey seal has a long flat vault which clearly distinguishes it from that of the common seal where the shorter, rounder vault gives rise to the dome-like head. The nasal bones too are differently placed so that the grey seal has, in the bull, a ‘roman’ nose profile and in the cow a straight or ‘grecian’ profile, while the common seal in both sexes shows a slight depression or ‘retroussé’ nose (Fig. 11 (#ulink_18dd6e49-bea7-5a3a-b718-1c14a5def608)). The young grey seal however has a skull very similar in appearance to that of the common seal and to that it owes its puppyish look. Within the first year the specific elongation and flattening of the skull takes place and there is little difficulty in distinguishing the two species in the field.

As grey seals grow older these characteristics are accentuated. At 5–6 years of age the sutures between the frontals, parietals, squamosals and occipitals fuse but the anterior sutures between frontals, nasals and premaxillae remain free throughout life and some increase in both length and breadth of the skull continues. In some of the oldest of the cows the profile may begin to take on a ‘roman’ bend, just as the young bulls approaching puberty still have such a straight profile that their identification by this character alone is by no means sure.

The teeth of the grey seal are very distinctive and unlike those of any other phocid. The formula is normally

and the dentition which erupts during puppyhood is the adult or definitive one. The milk dentition, in which the molars are not represented, is formed and resorbed in the foetal stages. The molars and premolars possess one large cusp and two others so small that often they appear to be missing (Fig. 12a (#ulink_4910a6c1-6dd0-5ba3-a295-b28759bfb95d)) (cf. common seal with three well developed cusps). Wear of the teeth is no criterion of age. Normally the teeth of the upper jaw fit between and behind those of the lower jaw but occasionally the jaws are relatively misplaced (prognathous) and the teeth meet over part or all of their basal area. In an extreme case the teeth of both jaws then become worn down to flattened stumps. One such has been recorded at only 11 years of age. Very few instances of diseased teeth have been found, although deformed and diseased conditions of the jaws are a little more frequent. It must be assumed that in such vital structures any major deficiency rapidly leads to semi-starvation, loss of condition and death.

FIG. 11. External differences between common and grey seals and between grey seal bulls and cows. Between grey and common seals the position of the nostrils is diagnostic and also the domed and rounded head of the common. Between grey seal bulls and cows the profile is the most certain distinguishing feature when only the head is visible above water. Common seal bulls and cows are almost impossible to separate by head features alone. (#ulink_22c6d989-fa9b-5409-b38b-54dea7aa3479)

In the bulls the canines are much larger than in the cows. Not only are they heavier, but the root is more bulbous. It is quite possible to sex an isolated lower jaw of any animal over the age of 5 years by the shape of the canine tooth. In the bulls the upper incisors are also broader and this results in a greater width between the canines. Externally these features unite in producing a broader muzzle and a greater gap between the nostrils in the male. The breadth of the male muzzle is further accentuated by the massive pads on which the vibrissae are mounted (Fig. 12 (#ulink_4910a6c1-6dd0-5ba3-a295-b28759bfb95d)).

FIG. 12. Jaws and teeth in the common and grey seals, A. shows the differences in the molar teeth of common and grey seals, B. shows the markedly broader muzzle in the bulls, C. shows the greater curvature in the canine teeth of bull grey seals, D. shows the greater depth in the lower jaw of bull grey seals. Both jaws are drawn to the same length.

(#ulink_f33a2c40-5f88-52ba-ac37-ff4dc44dd9ab)

The position and arrangement of the nostrils are also diagnostic features distinguishing grey from common seals. In the latter the two nostrils almost meet at their most anterior and ventral point and diverge above this at a distinct angle. In the grey seal the nostrils are almost parallel and their anterior ventral points are separated by a large pad of skin (Fig. 11 (#ulink_18dd6e49-bea7-5a3a-b718-1c14a5def608)).

The grey seal is highly vocal, particularly the cow. All aggression by cows, if only jostling for position in a haul-out, is accompanied by high-pitched hooting which has a peculiar quavering quality, partly of pitch and partly of volume. This hooting often carried out by several cows at once produces a weird sound which has been called ‘singing’ but it is far from singing at its best! The bulls are capable of a snarling hiss which also has a guttural quality. However, often in mild aggression they do no more than open their mouths and emit an exhalation which is almost soundless. The high pitched voice of the pup is described later (See here (#litres_trial_promo)).

There are many parts of Britain where the species of seal present can be almost certainly determined by the habitat. Thus, as Fraser Darling has said, the common seal on the west coast of Scotland is a sea-loch seal, the grey a seal of the outer islands and the strong Atlantic seas. And again on the Essex coast the mud and sand flats are typical haul-out sites for common seals, while the rock-bound coasts of west Wales provide typical grounds for the grey. Nevertheless it is not possible to generalise completely. Certainly the grey seal uses habitats which would rarely be used by common seals, isolated skerries and islands swept by Atlantic gales and surrounded by tidal rips which throw the sea into tumultuous heaps. The common seal will use estuarine waters and the mud and sand banks associated with them where the grey would never go. Yet between these extremes there are many habitats which both use. Many of the haul-outs in Orkney and Shetland are mixed, although of course the breeding grounds never are.