Allometry of diving capacity in air-breathing vertebrates

Maximum diving depths and durations were examined in relation to body mass for birds, marine mammals, and marine turtles. There were strong allometric relationships between these parameters (log 10 transformed) among air-breathing vertebrates (r = 0.71, n = 111 for depth; r = 0.84, n = 121 for duration), although there was considerable scatter around the regression lines. Many of the smaller taxonomic groups also had a strong allometric relationship between diving capacity (maximum depth and duration) and body mass. Notable exceptions were mysticete cetaceans and diving/flying birds, which displayed no relationship between maximum diving depth and body mass, and otariid seals, which showed no relationship between maximum diving depth or duration and body mass. Within the diving/flying bird group, only alcids showed a significant relationship (r = 0.81, n = 9 for depth). The diving capacities of penguins had the highest correlations with body mass (r = 0.81, n = 11 for depth; r = 0.93, n = 9 for duration), followed by those of odontocete cetaceans (r = 0.75, n = 21 for depth; r = 0.84, n = 22 for duration) and phocid seals (r = 0.70, n = 15 for depth; r = 0.59, n = 16 for duration). Mysticete cetaceans showed a strong relationship between maximum duration and body mass (r = 0.84, n = 9). Comparisons across the various groups indicated that alcids, penguins, and phocids are all exceptional divers relative to their masses and that mysticete cetaceans dive to shallower depths and for shorter periods than would be predicted from their size. Differences among groups, as well as the lack of relationships within some groups, could often be explained by factors such as the various ecological feeding niches these groups exploit, or by variations in the methods used to record their behavior.