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