170 | Chapter 9
Watch a cormorant or shag arch its body as it slips underwater, and
it is difficult to resist admiring a bird that appears so at ease below the
surface. Watch a video from a camera- carrying Imperial Shag, and the
impression is confirmed.^12 After submerging off Patagonian Argentina,
the bird descends for 40 seconds, its head bobbing in front of the back-
mounted camera. On reaching the bottom at 50 metres, the shag begins
searching, peering to left and right across a nearly featureless seabed.
After another 80 seconds it catches a fish with a single lunge. Time to
ascend. The light brightens, and air bubbles start to fizz forth from the
plumage. At the end of the 40 second ascent, the bird emerges into South
American daylight.
Cormorants and shags routinely search for prey close to the seabed
at depths of 30– 40 m but Imperial Shags, probably the best divers in the
group, have plunged to 145 m when breeding on the Crozets.^13 Since the
cormorants propel themselves underwater by feet, not wings, it might
be that the Flightless Cormorants of the Galapagos can reach the same
depths as their flighted cousins. This is broadly true. The maximum re-
corded depth is 73 m. However over 90 percent of their dives occur in
water less than 15 m deep whilst within a kilometre of the nest.^14 Scope
for plunging into the depths whilst remaining close to the coast is obvi-
ously limited.
The largest group of seabirds, the petrels and albatrosses, includes
species that do not dive. The loose- plumaged gadfly petrels are an exam-
ple. Other species may submerge but would not win any diving compe-
tition. Think, for example, of a Light- mantled Sooty Albatross splashing
down to four metres. However, among two petrel groups, there are seri-
ous divers, most obviously the diving petrels. Studies from 20 years ago,
using relatively inaccurate capillary recorders (Chapter 1), hinted that
these birds, weighing about the same as a large thrush, could reach 40 m.
More modern devices, based on solid state electronics, have yielded less
startling depths. Thus the South Georgia Diving Petrel, apparently
tending to hunt somewhat deeper than the Common Diving Petrel, typ-
ically dives to about 4 m during 14 second immersions, and may go as
deep as 18 m.^15
In contrast, technological improvements have not in the least reduced
the impressive depths reached by certain shearwaters that are well able