Penguins are often considered to be as ecologically and behaviourally homogenous as their morphology.
Their structural morphology and associated physiological adaptations are governed by the demands of
operating as flightless, subsurface marine predators. However, within the very strict constraints of this lifeform, penguins show considerable ecological and behavioural heterogeneity, although some of this undoubtedly
relates to the range of latitudes and biotopes in which penguins breed. In this paper we: (i) briefly
summarise and review some of the main features of the breeding biology, ecology and demography of
penguins; (ii) identify consistent patterns across species in the grouping of these features – and highlight
anomalies; (iii) suggest explanations/hypotheses for some of the potential links between ecology, behaviour
and demography within these groupings; (iv) investigate six topics containing potential paradoxes,
namely: migration, fasting, mate fidelity, brood reduction, demography and duration of breeding seasons.
We conclude that in many biological and ecological traits penguins can be divided into two groups: (i)
resident species, feeding inshore with short fasts ashore, breeding at an early age and having low divorce
rates, and; (ii) migrant species, feeding offshore with long fasts ashore, breeding at older ages and having
higher divorce rates. The placement of Magellanic Spheniscus magellanicus and Gentoo Pygoscelis papua
Penguins in opposite groups to their congeners is particularly intriguing. We suggest that trade-offs between
the year-round abundance and predictability of prey and the latitudinally-influenced time available for
breeding are important determinants of these patterns. Considerably improved basic biological and ecological
data on penguins and careful testing of explicit hypotheses will be required to investigate further both the
suggested patterns and the remaining paradoxes.
Authors: Croxall, J. P., Davis, L. S.
1 January, 1999
Marine Ornithology / 27