Time and Energy Constraints in Pinniped Lactation

Abstract

Previous reviews have recognized patterns of lactation in pinnipeds divided along phylogenetic lines. This study extended previous models of lactation in pinnipeds by explicitly taking into account all the energetic costs to mothers. Based on an analysis of time-energy budgets, the feasible lactation strategy for a species can be shown to depend on body mass. Due to increased metabolic costs of maintenance, species with a large body mass cannot normally sustain lactation by foraging during lactation unless they have access to rich local prey resources. Consequently, large pinnipeds must normally sustain lactation from body reserves. This disadvantage is compensated in large pinnipeds by freedom to forage in support of offspring at greater range whereas small pinnipeds are restricted to foraging within the locality of the pupping colony. In the absence of correlations between major life-history variables and body mass in pinnipeds, the principal patterns of lactation are likely to be different solutions to the trade-off between foraging on a relatively rich prey resource at long range and foraging on a poorer prey resource within a restricted range. Hence phylogeny may be less important than adaptation in the evolution of pinniped lactation.

Seasonal home ranges and fidelity to breeding sites among ringed seals

“…Inter-annual fidelity to small ranges has implications for the foraging ecology, breeding biology, and population structure of ringed seals. During lactation, breeding, and subsequent molting, phocid seals may be restricted in their movements for periods of a few weeks to 3 or 4 months (Costa 1991;Thompson et al 1994;Boyd 1998;Schulz and Bowen 2005). The ringed seals that we tracked were confined to very small ranges for up to 10 months each year.…”

“…The small under-ice home ranges maintained during the subnivean period allow lactating females to frequently attend the pups in subnivean lairs. Frequent visits to the lairs likely increase the efficiency of energy transfer to the pup (Boyd 1998;Lydersen et al 1992;Lydersen and Kovacs 1999) and minimize predation on pups by allowing their mothers to move them when predators attempt to excavate birth lairs (Taugbøl 1984;. The small size of the under-ice ranges, however, limits access to prey, and ringed seals may compensate by using ranges that correspond to areas of high prey density.…”

Capital Expenditure and Income (Foraging) during Pinniped Lactation: The Example of the Weddell Seal (Leptonychotes weddellii)

“…Thus, it is not clear that capital breeding is always more energetically costly than income breeding. A variety of other parameters, including animal size, food availability, transport costs, neonatal developmental state, and type of maternal care, are thought to be important to the evolution of capi- tal breeding systems (Boyd, 1998;Trillmich and Weissing, 2006;Houston et al, 2006).…”

“…Seals are the best-studied group of mammalian capital breeders (Oftedal et al, 1987a;Costa, 1991;Boness and Bowen, 1996;Boyd, 1998;Mellish et al, 2000;Oftedal, 2000;Schulz and Bowen, 2004). Otariid seals remain ashore for approximately one week after giving birth and transfer approximately 4% of body protein and 12% of body energy to their pups, after which they undertake regular foraging trips to sea (Oftedal et al, 1987a;Costa, 1991;Oftedal, 2000).…”

“…As the true seals (family Phocidae) encompass a wide spectrum from mixed capital-income to extreme capital breeding, this family is an excellent model system for testing hypotheses about the evolution of capital breeding strategies. Factors thought to have favored the evolution of extreme capital breeding in phocids include large body size (Boness and Bowen, 1996;Oftedal, 2000), limited availability of food (Boyd, 1998), the impact of unstable nursing substrates (Oftedal et al, 1987a;Lydersen and Kovacs, 1999), and reduction of maternal metabolic overhead costs (Fedak and Anderson, 1982;Costa, 1991).…”