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Lactation performance in polar bears is associated with fasting time and energetic state

December 29, 2023

Females must continually make resource allocation decisions because of fitness trade-offs between self-maintenance and investment in current offspring, yet factors underpinning these decisions are unresolved. Polar bears Ursus maritimus face considerable allocation challenges when seasonal sea-ice melt precludes access to prey for several months, and females rely solely on energy stores to cover their own energetic needs and provision offspring. We tested how female polar bears regulate lactation during onshore fasting (i.e. capital breeding) and determined the consequences of moderated lactation for females and cubs. Overall, milk energy declined, and lactation was more likely to cease with longer time fasting. Lactation was partially mediated by maternal energetic state and depended on litter characteristics. Milk energy declined more sharply with fasting time (~2.6 times more strongly) in females with 2 offspring compared to those with 1. Females with cubs-of-the-year produced higher energy milk than those with yearlings, and their milk energy also increased more strongly with maternal energy density. Milk energy declines benefited females via reduced depletion of maternal energy reserves, but cub growth decreased. Altered lactation investment likely has consequences for both female survival and the fate of offspring, which could scale up to influence population dynamics. Given that Arctic warming means polar bears across much of their range will experience longer periods without access to primary prey, our results underscore how lactation will likely become increasingly compromised.

Publication Year 2023
Title Lactation performance in polar bears is associated with fasting time and energetic state
DOI 10.3354/meps14382
Authors Louise C. Archer, Stephen N. Atkinson, Anthony M. Pagano, Stephanie R. Penk, Peter K. Molnár
Publication Type Article
Publication Subtype Journal Article
Series Title Marine Ecology Progress Series
Index ID 70255630
Record Source USGS Publications Warehouse
USGS Organization Alaska Science Center Ecosystems
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