tied to home | 89Finally there are species, for example the Short- tailed Shearwater,
where the males also depart the colony at about the same time as females
to prepare for the first long incubation spell. There is a mass exodus and
the colony is virtually empty in the run- up to laying.
Perhaps unexpected is the recent evidence from tracking studies that
males and females may head to distinctly different sea areas, even when
both are absent from the colony for a lengthy and roughly similar pe-
riod. Murphy’s Petrels, studied on Henderson Island by Tommy Clay
and myself, have a pre- laying exodus that lasts about six weeks. Birds
head south- west but the average maximum distance from the colony is
900 km greater for males (3,800 km) than females (2,900 km). Further
east in the Pacific, Matt Rayner discovered a comparable difference
among Chatham Petrels, the males’ exodus taking them, on average,
1,500 km further from the colony on Rangatira Island* than the females’
trek.^5 However, perhaps the most striking example comes from Barau’s
Petrels.
Barau’s Petrels were first described as recently as 1963. Most of the
world population nests near the jagged volcanic peaks of the French
Indian Ocean island of La Réunion. Soaring up to 3,000 metres, the
peaks generate swirling updrafts in the late afternoon which the petrels
exploit as elevators. When the petrels are lifted 2,000– 3,000 m upwards
from sea level to their high-altitude colonies as dusk approaches, so the
returning birds are saved energy. I observed this behaviour in 1974 when
sharing a mountain- top cave with local Creole peasants who were en-
joying a night out in the wilds. Not only was the cave shared. So too was
the chicken, which arrived alive and became chicken curry after a pen-
knife sawed open its throat.
For 6– 7 weeks before laying from late September to early November,
the Barau’s Petrels embark on their exodus. In the case of females, it
takes them 1,500– 2,000 km from La Réunion to seas south- east of south-
ern Madagascar.^6 Males generally go 1,000 km further to the waters of
the Agulhas slope off Mozambique and north- eastern South Africa. As-
sociated with this geographic difference is a difference in behaviour. The
overall trip speed is 21 km/h for males and a lower 15 km/h for females,
- (^) The study island in the Chatham group, east of New Zealand.