• pinnipeds;
  • maternal;
  • life history;
  • adaptation;
  • lactation;
  • milk composition;
  • body mass;
  • foraging behavior;
  • breeding substrate


Interspecific correlations are commonly used to explore the adaptive functions of life history traits in pinnipeds. Although adaptive conclusions are improved by the use of comparative methods that account for underlying phylogenetic relationships among species, they are still dependent on the quality of life history data. We collected pinniped species estimates for 12 maternal and offspring life history traits and evaluated these estimates based on sample size, duration of study, and methods used to obtain the data. Although excellent data exist for some species, high-quality estimates in all 33 species are not available for any of the traits studied. High-quality estimates of maternal postpartum mass are known for 12 species, neonate birth mass for 21, pup rate of mass gain for 12, lactation length for 10, and weaning mass for 10. High-quality estimates of milk composition, milk energy output, and maternal foraging behavior during lactation are limited to ≤ 50% of species, with a taxonomic bias favoring the larger phocid species. Obtaining data on small-bodied phocid species will be critical to gaining a better understanding of the relative roles of body size and phylogeny in the evolution of pinniped lactation strategies.