Walrus (Odobenus rosmarus) predation on adult thick-billed murres (Uria lomvia) at Coats Island, Nunavut, Canada

Mallory et al. 2004: Polar Research 23(1), 111–114 The walrus (Odobenus rosmarus) is a circumpolar pinniped that has a varied diet. Evidence from numerous studies indicates that both Pacifi c walrus (O. r. divergens Illiger) and Atlantic wal rus (O. r. rosmarus Linneaus) are top predators in some trophic webs. While the majority of their diet consists of benthic invertebrates, particularly mollusks (Mansfi eld 1958; Loughrey 1959; Fay 1982; Fay et al. 1984; Fisher & Stewart 1997), both traditional ecological knowledge and infrequent direct observation confi rm that walrus also consume seals, fi sh and whales (Mansfi eld 1958; Fay 1982; Lowry & Fay 1984), though in some of these instances walruses may have been foraging on carrion. Although it was initially suggested that feeding on higher level vertebrates represented aberrant behavior (Gray 1927; Vibe 1950), more recent investigation has demonstrated that it is a common feature of walrus feeding behaviour in both subspecies (Lowry & Fay 1984; Muir et al. 1995). We know little about possible foraging by walrus on marine birds. Fay et al. (1990) found a black guillemot (Cepphus grylle) in the stomach of a Pacifi c walrus, and they cited earlier, unconfi rmed studies which suggested that walrus occasionally consume “birds”. The only other published record of birds occurring in the diet of walrus was made by Donaldson et al. (1995), who watched walrus hunting and successfully capturing young thick-billed murres (Uria lomvia). None of the other large dietary studies (above) have made similar observations. Here we report on the hunting behaviour, attack and success rates, and food processing behaviour of Atlantic walrus we observed hunting adult thick-billed Walrus (Odobenus rosmarus) predation on adult thick-billed murres (Uria lomvia) at Coats Island, Nunavut, Canada