74 | Chapter 4
in Maria Dias’s paper,^28 I found it difficult to resist the temptation to
mumble sotto voce that the birds were anxious to get home as soon as
possible.
However a small minority, 8 percent, remain in the Canary Current
near the Salvages colony.^29 These ‘stay- at- home’ shearwaters are over-
whelmingly males and, on average, they arrive back at the colony three
weeks earlier than the birds that had visited the southern hemisphere.
It is the late- arriving birds that may have to skip breeding because there
is no longer room at the inn and all breeding sites are already tenanted.
There is therefore an apparently good reason for male Cory’s Shearwa-
ters to winter north of females.
Unfortunately this tidy explanation of a gender difference in the
choice of non- breeding area appears to founder for another species
where males and females have somewhat different migratory destina-
tions. The Balearic Shearwater is a Critically Endangered species breed-
ing in the western Mediterranean. After breeding, the birds pass through
the Strait of Gibraltar in early July and spend three months in the east-
ern Atlantic, favouring two areas, one off Portugal and the other off
Brittany. From an overall sample of 26, a study led by Tim Guilford
tantalisingly reported that the five birds choosing Brittany waters were
all females.^30 Subsequent work by Rhiannon Meir of Southampton’s
Institute of Oceanography has confirmed that males remain off Iberia
whilst females occur in roughly equal numbers off Iberia and Brittany.
However, from late September the birds, now clad in fresh plumage,
have returned to the Mediterranean and indeed visit the colony sporad-
ically for five months before their late February laying. It is difficult to
conceive that the apparently different distribution of males and females
during the Atlantic phase of the year has any impact on burrow occu-
pancy several months later.
***
The birds have finished breeding, and some have migrated immense dis-
tances. Several leisurely months lie ahead before the birds are compelled
to return to the breeding colony. Or perhaps the notion of leisure is
fanciful if the bird is a Northern Fulmar competing with 500 other ful-