where seabirds find food | 151horny and tough to be digested. The beaks vary from species to species,
enabling an expert like Imber to identify the squid species eaten by the
albatrosses. He found that the squid taken by Royal Albatrosses were
species that lived above the continental shelf and shelf break. Oceanic
squid species were much less prominent than in pellets coughed up by
Wandering Albatrosses. Hence Royal Albatrosses became ‘Kings of the
Shelf Break’, and exactly this predilection for scouring shelf break seas
was confirmed when, a few years later, the Taiaroa albatrosses were
tracked out to sea with GPS devices.^10
Emerging from this narrative is a theme of seabirds gathering to eat
wherever sea conditions are favourable for plankton growth. This is
certainly true of the world’s most spectacular aggregations of feeding
seabirds. They may occur over the continental shelf. For example the
Bering Sea in the northern summer provides feeding grounds for mil-
lions of breeding auks and further millions of Sooty and Short- tailed
Shearwaters that find it worthwhile to traverse the Equator to reach the
area and avoid the austral winter. Also supremely productive are the
cold currents flowing from the poles roughly parallel to the continental
margins. As they flow towards the Equator, so they peel away from the
continent thanks to the Coriolis effect. This draws cold nutrient- rich
water up from the deep, allowing plankton to flourish. That is why the
Humboldt Current off Peru, the Benguela Current off South Africa
and the California Current off the western United States are key fishing
grounds for birds and fishers alike, a coincidence of exploitation that
creates conservation problems as we shall see in Chapter 10.
High marine productivity is not exclusively associated with proxim-
ity to land. Also extremely important in generating favourable condi-
tions are ocean fronts, where different water bodies converge or diverge.
As when two Sumo wrestlers clash, so when two distinct water bodies
meet, there is shuddering turbulence. The level of the sea’s surface is
slightly higher than ‘normal’ at these confluences, an anomaly that can
be detected by satellite. If small planktonic creatures are forced to the
surface, they or the animals that eat them may become seabird prey.
Alternatively the front may be divergent; two water bodies separate,
with the result that the sea level anomaly is negative and cold waters are
drawn upward from depth to ‘plug the gap’. The outcome is continuing