Search

Assessment of placental expulsion time in Cape fur seal females based on the birth events observed during this study. Of the 51 mother-pup pairs included in the analysis, we witnessed 30 births (including 21 births with placenta expulsion monitored), and estimated the time of birth of the remaining 21 pups based on the detection of placenta by seagulls and considering that placenta expulsion occurred 30 minutes after birth in this species (27).

The Cape fur seal (Arctocephalus pusillus pusillus) is one of the most colonial mammal species in the world. Females exclusively nurse their pups for 9 to 11 months, during which they alternate frequent foraging trips at sea with suckling periods ashore. The survival of the pup thus depends on the ability of the mother-young pair to relocate each other among thousands of individuals. Previous work has demonstrated identity information encoded in pup-attraction (PAC) and female-attraction (FAC) calls. Here, we investigated vocal recognition between mother and pup using playback experiments of PAC and FAC performed during the breeding season at Pelican Point, Namibia. Both females and pups were able to specifically discriminate the voice of their pup or their mother. We reported the ability of females to memorize previous versions of their pup’s calls (evidence of recognition up to 73 days after pup’s calls recording). Vocal recognition was demonstrated in pups from 1 to 13 weeks age. Females and pups did not respond more strongly to the non-filial or non-mother for pups stimulus even if it had a strong acoustic similarity with the filial or mother stimulus. This suggested that Cape fur seal mother-pup pairs have high perceptual and cognitive abilities, allowing to specifically discriminate kin’s vocalizations in a very noisy and confusing environment.The Cape fur seal (Arctocephalus pusillus pusillus) is one of the most colonial mammal species in the world. Females exclusively nurse their pups for 9 to 11 months, during which they alternate frequent foraging trips at sea with suckling periods ashore. The survival of the pup thus depends on the ability of the mother-young pair to relocate each other among thousands of individuals. Previous work has demonstrated identity information encoded in pup-attraction (PAC) and female-attraction (FAC) calls. Here, we investigated vocal recognition between mother and pup using playback experiments of PAC and FAC performed during the breeding season at Pelican Point, Namibia. Both females and pups were able to specifically discriminate the voice of their pup or their mother. We reported the ability of females to memorize previous versions of their pup’s calls (evidence of recognition up to 73 days after pup’s calls recording). Vocal recognition was demonstrated in pups from 1 to 13 weeks age. Females and pups did not respond more strongly to the non-filial or non-mother for pups stimulus even if it had a strong acoustic similarity with the filial or mother stimulus. This suggested that Cape fur seal mother-pup pairs have high perceptual and cognitive abilities, allowing to specifically discriminate kin’s vocalizations in a very noisy and confusing environment.

The Cape fur seal is one of the most colonial mammal species in the world. Breeding colonies are composed of harems held by mature males (older than 10 years) with up to 30 females and their pups, while subadult males (younger and socially immature) are kept away from bulls’ territories. As with other pinnipeds, Cape fur seals are highly vocal and use acoustic signals in all their social interactions. Previous research revealed that barks - short vocalizations always produced in sequences – which are produced by males for territorial defence, mating behaviours and agonistic interactions, convey information about the sex, age-class and individual identity. This study investigated whether motivational cues such as the arousal state can be encoded in territorial males’ barks by analysing their acoustic features in multiple contexts of production. The bark rate (number of calls per unit of time) and the fundamental frequency were found to significantly increase during high arousal state interactions (confrontation vs. standard activity). Secondly, playback experiments revealed that Cape fur seal subadult males responded with a higher level of vigilance when territorial males’ barks had a faster bark rate. Decoding the arousal state of bulls' from their barks is a mechanism that will likely constitute an advantage for both bulls and by the subadult males by avoiding or reducing physical conflicts, and thereby reducing energy expenditure and the risk of injury. This study is the first evidence of Cape fur seals’ ability to use rhythm in their vocalizations to modulate their social interactions.

table S1. Coefficients of the two linear discriminants resulting from the LDAs performed on female-attraction calls by age-classes at Cape Cross and Pelican Point.

figure S2. Comparison of accuracy of prediction of female-attraction calls per ageclass, obtained by chance or using the balanced Random Forest algorithm performed with 9 variables (Dur, f0, Fmax1, Fmax2, Fmax3, Q25, Q75, Ebelow2000, Bdw12).

supplementary methods file

Supplementary Methods include detail on the statistical analyses conducted for classifying the pulsed signal types of Heaviside's dolphins. Also, these methods contain the relevant information, steps and figures used in the acoustic modelling of the detection range and active space of a NBHF click compared to a lower-frequency burst-pulse click.