where seabirds find food | 145were going. This prompts the thought that there is information avail-
able at a colony to help guide a bird towards food.
If birds know where they are going, they could each have their own
individual preferences or, as mentioned in the previous chapter, they
could be following a ‘Win/Stay: Lose/Shift’ strategy. If the latter, they
face a quandary after losing, and failing to find food. To shift at random
would appear a poor strategy; there is so much ocean to be searched.
One means of improving the chances of success might be to follow
birds that had been successful and were returning from the colony to
an active feeding area that had proved profitable on their last foray.
Using traditional observation, tests of this idea have not been especially
convincing – but there have been some encouraging results. For exam-
ple, breeding Common Guillemots often gather on the water at the foot
of colonies. Working in Newfoundland, Alan Burger wondered whether
these assemblages could be where those adults that have not been
blessed with recent fishing success obtain knowledge by watching their
returning fellow guillemots.^1 In 60 percent of departures, breeding
adults splashed down within this assembly zone, and were more likely
to do so if they had not recently delivered a meal, or had spent more
than an hour at the colony. Meals were subsequently delivered to chicks
after 69 percent of such splashdown departures, but after 82 percent of
direct departures.*
Another intriguing study was undertaken on Isla Pescadores,† off
the coast of Peru and set in the immensely productive waters of the
Humboldt Current. The island is home to many thousands of Guanay
Cormorants whose dried guano was once extensively harvested as fertil-
izer before the advent of petrochemical- based fertilizers. Henri Weimer-
skirch’s team used GPS tags to follow the Cormorants on their feeding
excursions and depth recorders to pinpoint where they dived and fed.^2
There was no correlation between a bird’s bearing when returning to
the island and the bearing of its next outward trip. That is evidence the
birds did not return to the same feeding zone from one trip to the next,
- (^) The difference is highly suggestive of better fishing success among directly- departing birds
but, in the jargon, not quite statistically significant.
† (^) Island of the Fishermen.