84 | A Navigational Diversion
tested from small colonies off the Tuscan coast of western Italy.^7 At the
beginning of an incubation stint,* the subject shearwaters were ferried
about 400 km westward to a release point around 100 km south of Mar-
seille and out of sight of land. Released birds fell into three groups;
control birds with no manipulation, magnetically disrupted birds carry-
ing a magnet glued to their heads, and birds unable to smell and termed
anosmic. The anosmic state was achieved by washing the olfactory mu-
cosa with zinc sulphate. This chemical treatment temporarily knocks
out of the sense of smell which returns in a matter of weeks.
Carrying tracking devices that allowed the research to plot the routes
taken, control and magnetically disrupted birds returned home fairly
directly. Apparently they could assess where they had been released and
orient accordingly, towards the east. Not so the anosmic birds. Their
initial orientation was towards the north, the French coast. Once in
sight of presumably familiar landmarks, they tended to follow the coast
homeward, and therefore took longer to reach the colony than the other
shearwaters.
Navigating seabirds variously use information from the sun, from
landmarks ashore, and from the pattern of smells, precise identity un-
known, carpeting the sea. But there remain further possibilities to be
explored. It would surprise me if they did not recognize the alteration
of the cloud patterns that can signal to mariners the presence of land
not yet visible over the horizon. More tantalizing – and totally without
any support at the time of writing – is the thought that seabirds, like the
Polynesian navigators of a thousand years ago, might be able to recog-
nize wave patterns on an oceanic scale and use these patterns, created
by the consistent interplay of prevailing winds and fixed land obstacles,
to assess their position.
- (^) Since incubation stints last a week or more, a bird removed from its egg early in the stint has
no immediate need to feed. It is also likely to be strongly motivated to return to its nesting
burrow. In the experiment any eggs at risk of predation in the parents’ absence were artificially
incubated.