Stomach Temperature Records Reveal Nursing Behaviour and Transition to Solid Food Consumption in an Unweaned Mammal, the Harbour Seal Pup (Phoca vitulina)

Abstract

Knowledge of milk transfer from mother to offspring and early solid food ingestions in mammals allows for a greater understanding of the factors affecting transition to nutritional independence and pre-weaning growth and survival. Yet studies monitoring suckling behaviour have often relied on visual observations, which might not accurately represent milk intake. We assessed the use of stomach temperature telemetry to monitor suckling and foraging behaviour in free-ranging harbour seal (Phoca vitulina) pups during lactation. Stomach temperature declines were analysed using principal component and cluster analyses, as well as trials using simulated stomachs resulting in a precise classification of stomach temperature drops into milk, seawater and solid food ingestions. Seawater and solid food ingestions represented on average 15.3±1.6% [0–40.0%] and 0.7±0.2% [0–13.0%], respectively, of individual ingestions. Overall, 63.7% of milk ingestions occurred while the pups were in the water, of which 13.9% were preceded by seawater ingestion. The average time between subsequent ingestions was significantly less for seawater than for milk ingestions. These results suggest that seawater ingestion might represent collateral ingestion during aquatic suckling attempts. Alternatively, as solid food ingestions (n = 19) were observed among 7 pups, seawater ingestion could result from missed prey capture attempts. This study shows that some harbour seals start ingesting prey while still being nursed, indicating that weaning occurs more gradually than previously thought in this species. Stomach temperature telemetry represents a promising method to study suckling behaviour in wild mammals and transition to nutritional independence in various endotherm species.

Making it through the first year: Ontogeny of movement and diving behavior in harbor seals from Svalbard, Norway

“…, Sauve et al . ). Thus, mothers and pups may not need to come back to land to nurse once pups are strong enough to nurse at sea; this would release the pairs to spend more time at sea, which might be part of the explanation for the increased amount of time spent in water as the pups grew older, documented in this study.…”

“…, Sauve et al . ) have focused on short periods, usually covering only nursing and the early postweaning period; no previous study has integrated information on both the development of movement patterns and diving behavior over a more extended period.…”

“…Sauvé et al . () documented that pups started foraging on small, easy‐to‐catch crustaceans in shallow water toward the end of lactation and thus started independent feeding before they were actually weaned. Consumption of a lot of invertebrate prey and little fish, in comparison to adult conspecifics, is a common pattern for young phocid seals (Nilssen et al .…”

“…In mammals, offspring growth and survival initially depend on parental nutritional provisioning (Klopfer 1981, Horning and Trillmich 1997, Gaillard et al 1998, Georges and Guinet 2000, Schwagmeyer and Mock 2008, Sauve et al 2014. But after the termination of parental care, the influence of abiotic environmental factors, population density, predation risks, and the offspring's body reserves and ability to forage efficiently in a given environment become key issues (Bowen 1991, Hastings and Testa 1998, Hastings et al 2012.…”

Challenges of measuring body temperatures of free-ranging birds and mammals

“…Stomach temperature sensors have also been used in conjunction with other temperature loggers to examine physiological processes such as hypothermia [71] and the heat increment of feeding [72]. More recently, stomach temperature sensors have been identified as a promising method to study the suckling behaviour and the transition to nutritional independence of pinnipeds [73,74].…”