ABSTRACT
Individual vocal signatures play an important role in parent-offspring recognition in many animals. One species that uses signature calls to accurately facilitate individual recognition is the bottlenose dolphin. Female dolphins and their calves will use their highly individualised signature whistles to identify and maintain contact with one another. Previous studies have shown high signature whistle rates of both mothers and calves during forced separations. In more natural settings, it appears that the calf vocalises more frequently to initiate reunions with its mother. However, little is known about the mechanisms a female dolphin may employ when there is strong motivation for her to reunite with her calf. In this study, we conducted a series of experimental trials in which we asked a female dolphin to retrieve either her wandering calf or a series of inanimate objects (control). Our results show that she used her vocal signature to actively recruit her calf, and produced no such signal when asked to retrieve the objects. This is the first study to clearly manipulate a dolphin's motivation to retrieve her calf with experimental controls. The results highlight that signature whistles are not only used in broadcasting individual identity, but that maternal signature whistle use is important in facilitating mother-calf reunions.
Subject(s)
Animal Communication , Bottle-Nosed Dolphin/physiology , Acoustic Stimulation/methods , Animals , Bottle-Nosed Dolphin/psychology , Female , Mother-Child Relations/psychology , Mothers/psychology , Sound Spectrography , Vocalization, Animal/physiologyABSTRACT
Object permanence, the ability to mentally represent and reason about objects that have disappeared from view, is a fundamental cognitive skill that has been extensively studied in human infants and terrestrial animals, but not in marine animals. A series of four experiments examined this ability in bottlenose dolphins (Tursiops truncatus). After being trained on a "find the object" game, dolphins were tested on visible and invisible displacement tasks, and transpositions. In Experiments 1 and 2, dolphins succeeded at visible displacements, but not at invisible displacements or transpositions. Experiment 3 showed that they were able to pass an invisible displacement task in which a person's hand rather than a container was used as the displacement device. However, follow-up controls suggested they did so by learning local rules rather than via a true representation of the movement of hidden objects. Experiment 4 demonstrated that the dolphins did not rely on such local rules to pass visible displacement tasks. Thus, like many terrestrial animals, dolphins are able to succeed on visible displacement tasks, but seem unable to succeed on tasks requiring the tracking of hidden objects.
Subject(s)
Bottle-Nosed Dolphin/psychology , Cognition , Animals , Awareness , Concept Formation , Female , Learning , MaleABSTRACT
In 2 experiments, bottlenose dolphins (Tursiops truncatus) judged the ordinal relationship between novel numerosities. The dolphins were first trained to choose the exemplar with the fewer number of items when presented with just a few specific comparisons (e.g., 2 vs. 6, 1 vs. 3, and 3 vs. 7). Generalization of this rule was then tested by presenting the dolphins with all possible pairwise comparisons between 1 and 8. The dolphins chose the exemplar with the fewer number of items at levels far above chance, showing that they could recognize and represent numerosities on an ordinal scale. Their pattern of errors was consistent with the idea of an underlying analog magnitude representation.
