Allo-suckling occurrence and its effect on lactation and nursing duration in harbour seals (Phoca vitulina) in Orkney, Scotland

Abstract

Fostering and allo-suckling are widespread among pinnipeds, and several hypotheses have been formulated to explain their occurrence. Here, we describe the occurrence of allo-suckling in harbour seals from photo-identification data of females and pups in Orkney (Scotland) during the pupping seasons between 2016 and 2019. We used a generalised linear model framework to investigate the effect of allo-suckling on the duration of lactation (females) and of nursing period (pups). A generalised additive model framework was used to explore how the probability of allo-suckling varied throughout the pupping season, and with changes in mother-pup separation time. Allo-suckling was observed in 31 females, at higher rates (18–37% of lactating females and 18–47% of the pups every year) than those observed in other phocid populations, with 13 females allo-suckling in multiple years. The duration of the pups’ nursing period was not affected by allo-suckling occurrence. However, females in mother-pup pairs where both mother and pup allo-suckled had longer lactation duration than when only the pup allo-suckled, or than in pairs where no allo-suckling was observed. The probability of allo-suckling increased during the pupping season and with increased mother-pup separation time. However, the proximate causes and the consequences on future reproductive output and pup survival remain unknown.Significance statementAllo-suckling, where females nurse others’ young, is widespread in pinnipeds, particularly among true seals. Given the high costs of lactation in pinnipeds, allo-suckling is a puzzling behaviour. Using photo-identification and field observations, we examined the occurrence of allo-suckling in harbour seals at a colony in Orkney, Scotland. We found that allo-suckling is common among seals at the study site, and at rates higher than reported elsewhere. Our results show that allo-suckling does not appear to affect the duration of the pups’ nursing period but does increase the lactation duration of females who suckle other pups and whose own pups also allo-suckle. This study highlights an area which requires further investigation as the energetic costs and benefits of allo-suckling remain poorly understood.

Movements and spatial usage of harbour seals in the Elbe estuary in Germany

“…The duration of the behavioural change is consistent with reported lactation durations. For instance, harbour seal mothers in Scotland suckle their pups for an average of 20 days, with a maximum lactation duration of 32 days 61 . Thus, the behavioural shift observed in the three females from this study is likely explained with parturition and lactation of a pup.…”

An observation of potential altruism by a male northern elephant seal (Mirounga angustirostris)

“…Allo‐parenting (adoption of orphaned young), a type of altruistic behavior, is commonly reported in social birds as well as mammals (Konig, 1997). Allo‐maternal care (nonmaternal care of young) has been noted in numerous pinniped species including in both Phocidae and Otariidae (Arso Civil et al, 2021; Gemmell, 2003). Male altruism, though, has rarely been described in marine mammals, including pinnipeds (Acevedo‐Gutierrez, 2009).…”

“…Kin selection (genetic relatedness ;Trivers, 1985) has been proposed to explain altruistic behavior in stable social groups, and specifically in pinnipeds such as harbor seal (Phoca vitulina; Arso Civil et al, 2021), Hawaiian monk seal (Neomonachus schauinslandi; Boness et al, 1998); Antarctic fur seal (Arctocephalus gazella; Gemmell, 2003), and gray seal (Halichoerus grypus; Pomeroy et al, 2000). Le Boeuf and Briggs (1977) speculated that kin associations might be even more pronounced for northern elephant seals because the species experienced severe genetic bottlenecks which resulted in depressed genetic diversity.…”

Estimating reproductive costs in marine mammal bioenergetic models: a review of current knowledge and data availability

“…In pinnipeds, observations of allonursing behavior are relatively widespread, having been observed in at least 5 phocids, odobenids and 11 otariids (e.g. Bartholomew, 1959;Riedman and Le Boeuf, 1982;Childerhouse and Gales, 2001;de Bruyn et al, 2010;Pitcher et al, 2011;Arso Civil et al, 2021). This behavior is often attributed to misdirected parental care (e.g.…”