Can a gray seal (Halichoerus grypus) generalize call classes?

Abstract

Past researchers have found that gray seals (Halichoerus grypus) are capable of classifying vocal signals by call type using a trained set, but were unable to generalize to novel exemplars (Shapiro, Slater, & Janik, 2004). Given the importance of auditory categorization in communication, it would be surprising if the animals were unable to generalize acoustically similar calls into classes. Here, we trained a juvenile gray seal to discriminate novel calls into 2 classes, "growls" and "moans," by vocally matching call types (i.e., the seal moaned when played a moan and growled when played a growl). Our method differed from the previous study as we trained the animal using a comparatively large set of exemplars with standardized durations, consisting of both the seal's own calls and those of 2 other seals. The seal successfully discriminated growls and moans for both her own (94% correct choices) and the other seals' (87% correct choices) calls. We used a generalized linear model (GLM) and found that the seal's performance significantly improved across test sessions, and that accuracy was higher during the first presentation of a sound from her own repertoire but decreased after multiple exposures. This pattern was not found for calls from unknown seals. Factor analysis for mixed data (FAMD) identified acoustic parameters that could be used to discriminate between call types and individuals. Growls and moans differed in noise, duration and frequency parameters, whereas individuals differed only in frequency. These data suggest that the seal could have gained information about both call type and caller identity using frequency cues.

Call Usage Learning by a Beluga (Delphinapterus leucas) in a Categorical Matching Task

“…Given the importance of auditory categorization in communication systems (Stansbury et al, 2015), and the anecdotal and experimental evidence of vocal imitation and plasticity in this species (Eaton, 1974;Murayama et al, 2014;Ridgway et al,1985), these results were unexpected. The following sections evaluate the various possible explanations for why this particular beluga showed difficulty mastering this vocal task.…”

“…Size of the training set. Stansbury et al (2015) argued convincingly that small training sets impact a subject's ability to generalize to novel stimuli. They re-created Shapiro et al's (2004) earlier categorical matching study on two grey seal pups, which were trained successfully to respond to playbacks of moans and $?!…”

“…A true understanding of the matching task requires not only that the subject associates a particular acoustic stimulus with a particular vocalization, but that it generalizes to a novel sample of this vocal type, and ultimately that it generalizes further to apply this not just to novel exemplars of the same category, but to novel categories, matching the stimulus regardless of the call type presented. Categorical vocal matching in marine mammals has been recently demonstrated experimentally for a gray seal, which could categorize and generalize between two call classes, "growls" and "moans" (Stansbury, de Freitas, Wu, & Janik, 2015). It is common in nature and mediates important aspects of social relationships in species in which it has been proven to exist.…”

Vocal production learning in mammals revisited

“…Pinnipeds are well known for their trainability in captivity and a number of studies have shown that they are capable of usage learning as demonstrated by conditioned production of calls in their repertoire [ 45 , 46 ]. Training studies on harbour seals ( Phoca vitulina ) [ 45 ] and walrus ( Odobenus rosmarus ) [ 47 ] have also shown that they can invent calls as judged by a trainer and increase the variability of their calls when rewarded accordingly.…”

Will Culling the Northwest Atlantic Gray Seal Population, Halichoerus grypus (Fabricius, 1791) (Carnivora: Phocidae) on Cape Cod, Massachusetts, USA Reduce the Risk of Human-White Shark Encounters?

“…Like the deer wasting disease example, annual culling would be needed to maintain any population control. Second, gray seals are relatively intelligent animals as demonstrated by their capacity for vocal learning (Shapiro et al 2004, Stansbury et al 2015 and as such likely possess a level of threat awareness at least as high as a badger or a fox. The likelihood that widespread culling would be perceived as a threat by the seals is high, potentially causing them to move to other areas of Cape Cod and increasing the risk of human-shark encounters in those currently unaffected areas.…”