Collins New Naturalist Library. H. Hewer R.

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) (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.

      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).

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.

      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).

      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).

      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.