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Can the sex of a Weddell seal (Leptonychotes weddellii) be identified by its surface call?
Abstract: Pinnipeds predominately use underwater vocalizations for social interactions during the breeding season. Knowing the sex of the vocalizing individual can be of significant value for interpreting aquatic behaviour. However, it is usually difflcult to identify the sex of the caller because the individual cannot be seen underwater. Weddell seals (Leptonychotes weddellii) produce a wide variety of underwater vocalizations, as well as a number of closed-mouth call types in air, which sound very similar to the underwater versions. This study used surface calls to determine whether Weddell seals produce sex-specific calls or whether there are differences in the attributes of calls made by both sexes. In-air recordings were made of adult male and female Weddell seals in breeding colonies near Davis Station, Antarctica. Trill call types were produced only by males in air, presumably underwater these are used for the purpose of territorial defence, advertisement, dominance and/or warning calls. Assuming males and females are equally likely to use the trill call type, the probability of a trill being part of the female repertoire, but not being recorded because of sample size problems, was less than 0.0001. The DL234 (roar) and DM (mew) call types also appeared to be male-specific calls, while, DWA242 (a whistle that increases in frequency in discrete steps) is a female-specific call. The DWAG call type (alternating ascending whistles and grunts) was used by both males and females; however, there were differences between the sexes in the start and end frequency measures. Assuming that what is heard in air is reflective of underwater calling, specific underwater call types could identify the sex of the caller in Weddell seals.
Key Words: WEDDELL SEAL; LEPTONYCHOTES WEDDELLII; VOCALIZATION; SEX-SPECIFIC; TRILL; CALL IDENTIFICATION.
Document Type: Research article