a navigational diversion | 83ford, England, developed personally- stereotyped routes to the home loft.
These routes were by no means the straightest possible. Rather they
appeared to connect a series of landmarks, or landscape features such as
main roads, leading in roughly the right direction.^5
The nuances of how a landbird might integrate information from the
sun and stars above, from its sense of the earth’s magnetic field, and
from its familiarity with the visible and olfactory landscape is beyond
the present discussion. It is time to ask whether the same abilities – or
others – are extended to seabirds.
From Geoffrey Matthews’ pioneer experiments with Manx Shear-
waters came hints of the use of the sun. This possibility has recently been
given further credence by Ollie Padget of the OxNav group. Instead of
clock- shifting caged birds, the approach traditionally applied to land-
birds, Padget was able to clock- shift incubating Manx Shearwaters while
they sat on the egg in the burrow. When the subject shearwaters were
taken some 50 km from the colony on Skomer, and released, their home-
ward journeys differed from the ‘correct’ route in a manner consistent
with the time shift. Even though the birds were released in seas they will
assuredly have visited previously in their lives, the clock- shift effect per-
sisted right until the birds were within 8 km of Skomer, at which dis-
tance the breeding island was certainly in view.
Although the use of a magnetic sense by migrating landbirds is be-
yond dispute, a similar sense has yet to be demonstrated in seabirds. In-
deed the failure of several tests specifically designed to deliver evidence
of such a sense gives reason to wonder whether seabirds absolutely lack
this ability. For example, Wandering and Black- browed Albatrosses and
White- chinned Petrels have all been despatched across the Southern
Ocean bearing head- mounted magnets sufficiently strong to confound
the birds’ perception of the earth’s magnetic field.^6 No test yielded any
evidence that the bird’s ability to forage successfully or to return expe-
ditiously to its home colony was impaired. In every experiment, other
senses, notably sight and smell, were available to aid the magnetically-
impaired birds so the evidence for a lack of magnetic sense is by no
means conclusive. But one wonders...
Given that smell helps seabirds find food (Chapter 8), it is no sur-
prise that there is good evidence that it also helps them traverse their
salty domain. One strand of evidence comes from Scopoli’s Shearwaters