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

Caroline C Sauvé,Joanie Van De Walle,John P Y Arnould,Mike O Hammill,Gwénaël Beauplet,Yan Ropert-Coudert

doi:10.1371/journal.pone.0090329

Caroline C Sauvé, Joanie Van De Walle + Show 4 more

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https://doi.org/10.1371/journal.pone.0090329

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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.

Highlights

During the period of parental dependence, offspring growth and survival rely on parental nutritional provisioning, mostly determined by maternal milk transfer in mammals [1,2]
While one factor exhibited important loadings for the variables related to the duration of the PDER events, the variables associated with temperature decrease heavily loaded on the other factor (Table 3)
PDER event detection and possible sources of variation Through the use of multivariate statistical analysis coupled with laboratory simulations of ingestion events, we have demonstrated that stomach temperature telemetry allows a fine discrimination between the three possible ingestion types in harbour seal pups

Summary

Introduction

During the period of parental dependence, offspring growth and survival rely on parental nutritional provisioning, mostly determined by maternal milk transfer in mammals [1,2]. Otariid pups begin to consume solid food near the end of the lactation period [12,16], making the transition to nutritional independence more gradual in otariids than in phocids In spite of these phylogenetic distinctions, females of some phocid species do not follow the typical phocid maternal strategy as they forage in the course of the lactation period [17,18,19,20,]. Harbour seal females undertake foraging trips at sea beyond the first week of lactation [19,21] This ‘otariid-type’ maternal strategy is thought to be due to the inability of females to store sufficient energy and support milk production throughout the lactation period [11]. It is generally considered that weaning in this species is abrupt as in most phocids [25]

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