96 | Chapter 5
the larder for the weekend, it is not obvious why they go where they go.
The area targeted by the birds from Henderson is merely moderately
productive. Perhaps the extra 1,000 km needed to reach the immensely
rich seas of the Humboldt current would be a flight too far. Or perhaps
Murphy’s Petrels are unable to compete among dense milling aggrega-
tions of birds at food hotspots, and fare better where food is scattered
and can be exploited solitarily and relatively economically thanks to
their buoyant flight. At least the birds minimize the energetic costs of
the great journey by generally travelling along an anti- clockwise loop,
which provides the benefit of following winds as they head eastward on
the outward journey and westward when homebound on a more north-
ern track (see also page 120).
Contributing to the vast journeys of Murphy’s Petrels is the scarcity
of food in the blue emptiness of the tropical South Pacific surrounding
their nesting island. However, species breeding near more productive
waters also sometimes fly huge distances from the colony during incu-
bation. A nice example comes from the Northern Fulmars breeding on
Eynhallow. During incubation, off- duty birds typically remain within
100 km of this Orkney colony or perhaps venture further into the North
Sea. But in 2012, one male flew 2,500 km west to the Mid- Atlantic
Ridge.^14 He foraged over productive areas of persistent thermal ocean-
surface fronts along the Ridge’s Charlie- Gibbs Fracture Zone, and trav-
elled over 6,200 km in 14.9 days before returning to relieve his mate.
Looking at his track, it is difficult not to suspect that he knew where he
was heading as he left the Orkneys! (See Map 5.)
The penguins are the second group that endure long incubation spells.
Incubation stints of two to three weeks are the norm in several species.
But, for the obvious reason that swimming is much, much slower than
flying, off- duty penguins travel but a small fraction of the distance trav-
elled by petrels. For example, ten male Rockhopper Penguins tracked by
satellite from colonies in the north-east of the Falkland Islands headed
north- east away from land.^15 Three concentrated their foraging over the
slope of the Patagonian Shelf about 150 km from home and returned in
two weeks. The other seven went further north, up to 350 km from the
colony, to which they returned after some three to four weeks. The mean