A Navigational Diversion
Seabirds routinely make prodigious journeys across immense oceans,
feats which instantly raise questions about their powers of navigation.
Conceptually, navigation can be divided into two more or less distinct
elements. The first is orientation, the capacity to follow a roughly direct
route from the present position to the destination. In humans, this might
involve following a compass direction from Point A to Point B. In birds,
it might involve flying in a straight line between the breeding area and
the wintering grounds, guided by an internal compass using cues whose
identity I shall shortly address. The second element of successful naviga-
tion is a ‘map’ of the world, a sense of one’s present position in relation
to a destination.
Remarkably, the first convincing demonstration that birds indeed
have a map sense involved a familiar seabird, the Manx Shearwater. The
experiments, conducted by the late Geoffrey Matthews in the 1950s,
involved transporting breeding birds from their burrows to release
points that were hundreds of kilometres from the colony and, crucially,
were beyond the areas that even so prodigious a wanderer as the Manx
Shearwater would ever have visited.
Arguably the key tests were undertaken on incubating birds, known
from prior experiments to be the most ready to make a rapid passage
homeward. Transported from the colony on Skokholm, west of Wales,
to various inland points around England, the birds showed a strong
tendency to head immediately towards Skokholm when released under
sunny skies. And some birds reached their home burrow and waiting egg
so rapidly that they must have flown virtually straight across country.
The tendency to orient towards home at the outset largely vanished if
the birds were released under heavy cloud.
Intriguingly some birds were consistently quick at returning, others
consistently slow. Such consistency would not be anticipated if a rapid
return was simply due to a random, albeit fortunate, choice of route,
and so that very consistency among individuals is evidence of naviga-
tional ability.