where seabirds find food | 155favoured by seabirds in many parts of the world. For example, countless
thousands of Macaroni Penguins and Antarctic Fur Seals head to a feed-
ing area around 100 km north- west of South Georgia. Hereabouts the
Antarctic Circumpolar Current is nudged towards the surface; its up-
welling underpins the immense concentrations of krill that are then
consumed by hungry penguins and seals.
Without question seabirds concentrate where marine productivity is
highest. Where it is low, birds are few and far between. I have sailed
(reluctantly) across the blue and unproductive* waters of the central
South Pacific and seen one bird, a gadfly petrel, between the sun’s rising
and setting. Between those extremes of highest and lowest productivity,
there are of course intermediate areas by no means bereft of birds. Nu-
merous modern studies have explored where, within those areas, birds
concentrate their activities, making use of the fact that satellite data are
readily available for sea surface temperature and for the concentration
of chlorophyll.
For example, using geolocators, a Portuguese team tracked the pere-
grinations of 17 Desertas Petrels during the summer breeding season
when they were nesting on Bugio, lying off Madeira.^15 The birds were
most active in the central North Atlantic around 40°N, about ten de-
grees of latitude north of the colony. Here chlorophyll concentrations
were higher than near Madeira but not so high as those found another
ten degrees further north. That raises the question of why the petrels,
for whom 1,000 km is barely an obstacle, did not head farther north. It
is a question to be re- visited later in the chapter.
The study extended into winter and the Desertas Petrels were noth-
ing if not scattered by their pursuit of favoured areas, areas first de-
scribed in Chapter 7. They were found beside the Gulf Stream off the
United States, around the Cape Verdes south of Madeira, in two south-
ern hemisphere sea areas respectively off north- east and south- east Bra-
zil, and in the central South Atlantic. In seeking suitable seas, the birds
selected areas on the west and east of the Atlantic, and north and south
- (^) The blue clarity of the water is a direct consequence of the paucity of plankton – and life – in
the surface layers.