The upcall is the most commonly detected and prevalent vocalization of the southern right whales’ (Eubalaena australis) vocal repertoire. This vocalization is similar among populations, is used by all sexes and age classes, as well as over a range of behavioural contexts, and thus, it is commonly used as a basis for passive acoustic monitoring (PAM) studies on this species. Efficiency of PAM methods depends on the ability to detect and correctly interpret acoustic signals, but previous studies report difficulties to distinguish between southern right whale upcalls and similar humpback whale (Megaptera novaeangliae) vocalizations. Recently, vocalizations similar to southern right whale upcalls were detected off Elephant Island, Antarctica, which forms an important feeding ground also for other baleen whales including humpback whales which are also acoustically present in the data. The similarity between southern right whale upcalls and humpback whale vocalizations complicates distinguishing between the two with certainty, as has also been reported by previous studies. In this study, we structurally analysed these vocalizations and compared call characteristics to a) confirmed southern right whale vocalizations recorded off Argentina and b) confirmed humpback whale vocalizations recorded in the Atlantic Sector of the Southern Ocean. Based on call features, detected upcalls off Elephant Island could be attributed to southern right whales. Apart from a similar mean duration, southern right whale upcalls had a notably lower frequency range compared to humpback whale vocalizations. Measurements describing slope and bandwidth were identified as the main differences in call characteristics between species. Moreover, vocalization parameters of analysed southern right whale upcalls were broadly similar to mean values of previous studies on southern right whale vocalizations. Surprisingly, compared to the upcalls from Argentina and from other previous studies, a shift in low frequency limits to higher frequencies was observed in the detected upcalls off Elephant Island. Potential drivers of this shift, such as anthropogenic noise and acoustic niche development in regard of sympatric species, are discussed. An acoustic energy analysis suggests fin whale (Balaenoptera physalus) acoustic activity off Elephant Island as a cause of high levels of low frequency background noise, potentially functioning as a driver for the shift of low frequency limits in southern right whales off Elephant Island. Confirming the acoustic presence of southern right whales in waters off Elephant Island, provides further support that these waters form an important foraging ground for multiple species. With the newly gained knowledge from this study, additional data can be analysed and provide insights in temporal occurrence and migratory behaviour of southern right whales in Antarctic waters.