tied to home | 103Masked Booby, there is also a particularly striking difference in call; a
bold honking by the female and a plaintive whistle from the male. It is
she who delivers more food to the chicks. In the Brown Booby, a species
whose clean- cut chocolate- brown and white plumage is a triumph of
graphic design, the larger female makes longer journeys than her mate
when they are searching for sardines in the Gulf of California, albeit
journeys that would barely make a petrel sweat. The female’s journeys
last for three hours, rather than the male’s two, and take her 40 km from
the colony, rather than his 17 km.^22
A sexual contrast of a very different nature has emerged from studies
of Southern Hemisphere shags. It has been best documented among the
Imperial Shags of Argentina where males are about 18 percent heavier
than females. With poorly-waterproofed plumage, this is a species that
spends the night ashore. One might guess that birds would first enter
the water around dawn and finally come ashore around dusk. This is
exactly what birds, studied in southern Argentina via geolocators and
immersion loggers, routinely do outside the breeding season. But, during
incubation and early chick- rearing, the females enter the water at dawn
and come ashore at midday. That is the cue for the males to go into the
water, from which they finally emerge at dusk. For part of the year, it is
a clear instance of ‘ladies first’.^23 Assuming this difference is not the re-
sult of masculine politeness, the study’s authors struggle to explain it.
Possibly the larger male can better defend the nest, and more readily
adjust his afternoon feeding schedule if his mate is late returning after
an unsatisfactory morning.
There is something preposterously self- important about a male frig-
atebird inflating his red throat pouch. But it works. It not only attracts
a mate but, unusually among seabirds, she is a mate who tolerates his
steady withdrawal from chick- feeding which may last (for her) a re-
markable 15 months.* Indeed differences in the chick- feeding behaviour
may begin as early as the brooding period. Studying Christmas Island
- (^) This includes feeding after the chick has fledged; see page 35. Normally, as mentioned in
Chapter 4, seabirds retain the same mate year after year. The fact that the female frigatebird
cares for the chick for far longer than does the male doubtless contributes to their failure to
follow standard seabird practice. Among frigatebirds successive breeding attempts are with
different partners.