• Jaakkola, K., Guarino, E., Rodriguez, M., Erb, L., & Trone, M. (2010). What do dolphins (Tursiops truncatus) understand about hidden objects?  Animal Cognition, 13, 103-120.

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.

For the full text of this article, please email drc-res@dolphins.org.

Fetal echocardiography represents the most important tool for the assessment of the cardiovascular well-being of the human fetus. Because of logistic, anatomic and behavioral challenges, detailed fetal echocardiographic evaluation of marine mammals has not been previously described. We sought to develop an approach to evaluating the fetal dolphin’s cardiovascular status using conventional, fetal echocardiographic techniques developed in humans. We evaluated eight singleton fetal bottlenose dolphins, each between 6 and 11 months gestation; 6 fetuses underwent two fetal echocardiographic evaluations each, 4 at 3 month intervals, and 2 at 0.5 month intervals. Evaluations were performed, without sedation, using a conventional, portable ultrasound system. Multiple transducers, probe positions, and maternal dolphin positions were utilized to maximize image quality. Fetal echocardiography included two-dimensional imaging and color flow mapping of the heart and great arteries, as well as pulsed Doppler evaluation of the umbilical artery and vein. A thorough evaluation of the fetal dolphins’ cardiovascular status was performed, with the greatest resolution between 8-9 months gestation. We demonstrated normal structure and function of the heart and great arteries, including the pulmonary veins, inferior vena cava, right and left atria, foramen ovale, tricuspid and mitral valves, right and left ventricles, ventricular septum, pulmonary and aortic valves, main pulmonary artery and ascending aorta. Pulsed Doppler techniques demonstrated normal umbilical arterial and venous waveforms, and color flow mapping demonstrated absence of significant valvar regurgitation. We conclude that fetal echocardiography, between 6-11 months gestation, can provide a safe and detailed assessment of the cardiovascular status of the fetal bottlenose dolphin.

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.

For the full text of this article, please email drc-res@dolphins.org.

Humans respond adaptively to uncertainty by escaping or seeking additional information. To foster a comparative study of uncertainty processes, we asked whether humans and a bottlenose dolphin (Tursiops truncatus) would use similarly a psychophysical uncertain response. Human observers and the dolphin were given 2 primary discrimination responses and a way to escape chosen trials into easier ones. Humans escaped sparingly from the most difficult trials near threshold that left them demonstrably uncertain of the stimulus. The dolphin performed nearly identically. The behavior of both species is considered from the perspectives of signal detection theory and optimality theory, and its appropriate interpretation is discussed. Human and dolphin uncertain responses seem to be interesting cognitive analogs and may depend on cognitive or controlled decisional mechanisms. The capacity to monitor ongoing cognition, and use uncertainty appropriately, would be a valuable adaptation for animal minds. This recommends uncertainty processes as an important but neglected area for future comparative research.

The behavior of dolphins in four Swim-With-Dolphin programs was compared by type of Swim encounter, defined by the presence ("Controlled") or absence ("Not-Controlled") of explicit trainer regulation of interactions between dolphins and human swimmers. Dolphin-swimmer interactions involving aggressive, submissive, or sexual behavior were designated as "high-risk" in the Swim context; sexual behavior was included as high-risk based on analyses that demonstrated co-occurrence of sexual and agonistic behaviors. High-risk activity comprised a substantial proportion of dolphin-swimmer social activity during Not-Controlled Swims. In contrast, high-risk activity rarely occurred during Controlled Swims, even though agonistic and sexual behaviors were normal components of the same dolphins' free-time social repertoire. These results indicated that direct trainer control of dolphin-swimmer interactions virtually eliminated high-risk activity from the Swim context, and thereby diminished the potential for dolphin distress, swimmer injury, and rejection of dolphins from Swim programs due to swimmer injury. This study illustrates effective use of quantitative behavioral sampling techniques for evaluation of captive management concerns and promotes broader use of these techniques for a better understanding of cetacean behavior.

Orienting nonverbal responses and verbal responses of eight children with mental disabilities interacting in water with dolphins and in water with favorite toys away from dolphins were recorded and analyzed on videotape. Significant improvements in hierarchal cognition responses occurred when interaction with dolphins was used as a favorite toy. Water work with dolphins evoked a greater number of and higher level responses than without dolphins.

Atlantic bottlenose dolphins were used to help increase cognition for mentally retarded children. Six mentally retarded boys were taught new vocabulary words through interaction with dolphins. Novelty, prior learning, order and position effects were all controlled. A multiple baseline across subjects single subject research design was used to assess the effect of interaction with dolphins on speech and memory. Line drawings were presented on boards in treatment in the water by humans and dolphins and in baseline in a classroom away from the dolphins. All research was videotaped. Results indicated children learned two to ten times faster and with greater retention when working with dolphins. Benefits include new evidence of the efficacy of using nonhuman species to help humans improve cognition.

Two trained bottlenose dolphins, Tursiops truncatus, were tested for their ability to detect visually 12 different oils and 22 oil mixtures confined at the surface in small cylinders. Detection thresholds were established in tests using progressively lighter substances. The animals detected 6-mm slicks of crude, residual, and refined motor oils, and diesel slicks thicker than 17 mm. They could not detect 6-mm thicknesses of leaded gasoline or transparent mineral oil. One dolphin's ability to detect oil improved with experience. While blindfolded, one dolphin could detect 12-mm-thick samples of two crude oils, Bunker C and mineral oil, but only when the latter two were churned and contained air bubbles. We conclude that dolphins detect the thicker concentrations of oil that occur near the source of an oceanic spill, but not lightly colored or refined products that tend to disperse into thin films.

Three captive bottlenose dolphins, Tursiops truncatus, were observed in an ocean pen measuring 14 × 11 m, divided into three equal areas by oil-containment booms. Each dolphin was placed in the pen alone for 4 d with no oil present, and 2 d with dark-colored mineral oil in one of the areas. We noted their area of surfacing, underwater movements, dive times, and reactions. After a few brief contacts with the oil, dolphins completely avoided surfacing in the slick. The oil also acted as a temporary barrier restricting their underwater movement.

In daylight, and again at night under a shading canopy, we observed the behavior of bottlenose dolphins (Tursiops truncatus) allowed to swim freely in a pool with three surface divisions, one of which contained either clear mineral oil, dark-tinted mineral oil, or a thin sheen of refined motor oil. Overall, they avoided oil both during the day and at night. The response broke down when we presented them with a thin sheen, especially at night; we suggest that such conditions represent the threshold for their ability to detect oil or their desire to avoid it. Irrespective of light conditions, the dolphins' tactile sense played a more important role than vision in perceiving, and ultimately avoiding, oil. The strength of their basic reaction dampens our fear that they might be unknowingly subjected to prolonged or repeated exposure to oil at sea.