Société nationale de protection de la nature et d'acclimatation de France, Paris (FRA)
Abstract
The striking convergences in morphology, behaviour and
physiology existing between various species of sea birds are discussed,
both on the basis of personal observations, mostly carried
out in the Antarctic and Sub Antarctic zones, and from data in the literature.
The morphological adaptations are reviewed first. The body
weight of species nesting underground is shown to be lighter than that of species nesting above ground. Plankton-feeders usually
have a broad bill, while fish-feeders have a long and narrow one.
There is a broad and continuons range of flight capabilities, ranging
from frigate-birds and albatrosses at one extreme to flightless
penguins at the other. The difficulty of a proper comparison of
flight and diving abilities between different categories of sea birds
is pointed out, and the results given by various measurements and
indices are compared.
The adaptive value of cryptic coloration of both eggs and
nestlings to their background is discussed, as well as the prolective
role of some immature and adult plumages. The adaptive function
of sea bird ritualized displays and vocalizations is suggested.
Further data supporting David Lack's (1968) conclusions on
the adaptive value of variations in egg weight and incubation
length are provided. Most sea birds have a low reproductive rate
which is counter-balanced by a relatively high survival rate. They
can be considered K-strategists.
Some estimates of the resting metabolic rate of adult sea birds are given.
The interdependence of the various adaptations is emphasized.
To better understand the variety of adaptive strategies displayed
by sea birds, the factors which are responsible for the heterogeneity
of the oceanic environment are reviewed. Further, the variations
in foraging distances observed in the various bird groups during
the breeding season in emphasized (fig. 11). Foraging distance is
significantly correlated with the average number of eggs produced
per year per female, and with the aspect ratio of the win