THE SOUTHERN SEA LION 307 



CAUSES OF DEATH 



A considerable number of pups are always found dead on the rookeries and many 

 more must escape observation. Towards the end of the breeding season I went over 

 the site of a rookery where the average number of pups had been 255. Fifteen dead 

 pups were found in various stages of decomposition and these alone indicate a death-rate 

 of 5-6 per cent before the break up of the harems and before the onset of winter 

 conditions. The true death-rate is higher, since the young pups are frail and dead ones 

 will soon be stamped out of sight and out of all recognition by the crowd of living seal. 



After the breeding season pups are often met with in a state of extreme emaciation, 

 either very sick or dead, and post-mortem examination shows an Uncinaria infection 

 and a blood-stained condition of the mucus which fills the intestines. The parasite is 

 probably the cause of the sickly condition and eventually of death. 



Some loss may be attributed to isolation due to the possession of a single cow by 

 a bull. These groups are often found detached and sometimes remote from the rookeries, 

 and the two adults seem particularly liable to wander, with the frequent result that 

 they do not come back and the pup is left to die. The solitary cow goes away to feed, 

 and is probably drawn towards a crowded part of the beach on her return journey 

 and is thereafter unable to find her former position on the shore (see p. 293). The bull 

 which had been her master would return to some place where his sexual impulse had 

 more opportunity of being satisfied. Even on the rookeries pups die of starvation through 

 wandering away at an early age or through the cows failing to return to their own places. 



The violence of their own species is the cause of some deaths: cows will handle 

 strange pups very roughly. One young pup, only a few days old, was found dead with 

 deep wounds in the liver where the fangs of an older seal had crushed into it and there 

 had been extensive bleeding into the coelom. I have seen a large immature male chase 

 a pup and throw it about when caught, apparently for amusement. 



Young immature sea lions are often found dead in winter; their frequency shows 

 that the death-rate is higher then than it is when they become older, for the more 

 advanced immature animals are practically never found dead. Of these young animals 

 five skulls were collected from specimens which could be dealt with. I was not able 

 to find any cause of death ; most of the animals were tolerably fat and some at any 

 rate had died where they lay, above high-water mark; but others were found below 

 on the tidal beach, sometimes wrapped in masses of kelp thrown up by heavy seas. 

 Some of these animals were probably drowned, as is almost inevitable in a species 

 which has at times to swim off shore against a heavy sea ; but this would only explain 

 part of these deaths. Birds of prey, probably giant petrels, often completely eviscerate 

 dead seals which they find on the beach, either through the natural openings or through 

 quite a small hole torn in the axilla where the skin is thin (cf. Matthews, 1929, p. 573). 



Of older sea lions one harem bull died in the middle of a rookery in the height of 

 the season ; he had no wounds visible from a distance, nor had he seemed to be sick 

 when I saw him, which was almost every day: some time afterwards I was able to 

 examine the carcase at close quarters, when it was considerably decomposed, but no 



