50 | Chapter 3
age reverse one trend but continue another. They spend a little more
time on the water than five- month juveniles but travel further. Have they
now mastered flight? Finally, adults spend more time on the water and
cover fewer kilometres per day than the immatures. Perhaps the adults
refined their fish- and squid- snatching skills to such an extent that they
can fulfil their daily energy needs with less effort.
Completely compatible with the argument that seabirds begin breed-
ing when the benefits exceed the costs is the possibility that feeding
skills may continue to improve, even after first breeding. Such has been
found in Cory’s Shearwaters, a species named after a wealthy American,
Charles Barney Cory, who was once the golfing champion of Florida.
The shearwaters breed on islands of the north- east Atlantic, including
the small Berlengas archipelago off Portugal. Here, almost 40 male shear-
waters were tracked with GPS loggers in the period immediately before
the males’ partners laid. The males were split into two groups, the inex-
perienced with a record of two or fewer breeding successes and the suc-
cessful with more than two successes. The experienced males consistently
concentrated in productive waters close to the Portuguese coast while
the inexperienced roamed more widely into less productive seas further
offshore, especially in the years when overall conditions were probably
poorer.^8 Perhaps these positional differences, supported by stable isotope
differences between the two groups, arise because the younger breeders
are still honing their feeding skills and/or learning the likely where-
abouts of a shearwater’s supper.
The age- related changes in foraging areas used do not stop after the
early breeding years. I have already mentioned how juvenile Wandering
Albatrosses operate north of older birds. Remarkably, there are con-
tinuing shifts among breeding birds, principally among the males. In a
paper aptly titled ‘Lifetime foraging patterns of the Wandering Alba-
tross: Life on the move!’, Henri Weimerskirch^9 details how the latitudes
used by female albatrosses, when on feeding trips during incubation,
shift little with age. They remain around 40°S. Males visit similar lati-
tudes to females in their early breeding years, say at 10 years old. There-
after they steadily shift southward, in marked contrast to females. By
the time he is 40, becoming ever whiter of plumage, and showing signs
of senility (and therefore lower annual survival), a male’s trip is likely to