research

Our lab has a long history of research on auditory biology, and the hearing adaptations that allow amphibious marine mammals to use acoustic cues while at sea and ashore. We would like to understand how animals perceive the acoustic world and to learn more about how noise influences their ability to detect important sounds. Because the animals we study are amphibious—foraging at sea but remaining tied to land for activities such as pupping and molting—we investigate their hearing both above and below the water's surface. A major impetus for this work is concern about increasing levels of noise in the oceans, from sources including shipping, ocean exploration, and military operations.

We first establish auditory profiles for different species by testing their hearing in air and in water at a range of frequencies. From this information we generate audiograms, or hearing curves, that allow us to determine frequency ranges of hearing, regions of best hearing sensitivity, and how hearing sensitivities in different media correlate to differences in life history. To expand these auditory profiles, we examine the effects of noise on hearing using other experimental procedures. Masking experiments, which involve signal detection against a noisy background, help us to assess how the simultaneous presence of noise affects hearing. Temporary threshold shift (TTS) experiments, which involve signal detection following exposure to noise, allow us to evaluate the residual effects of noisy backgrounds on hearing. These types of experiments are conducted with both simple and complex (real-world) stimuli. The results of our research are used to generate models predicting how noise of a given intensity, duration, or character will affect the hearing of free-ranging animals. Ultimately, these data are used by regulatory agencies charged with protecting pinnipeds and other marine mammals from the potentially damaging effects of anthropogenic noise.

We have had the opportunity to study the hearing abilities of lots of marine mammal species, including California and Steller sea lions, harbor seals, elephant seals, spotted seals, ringed seals, bearded seals, Hawaiian monk seals, walruses, and sea otters. All this information helps us to understand how groups of species are similar or different, and why.

Nowhere on Earth are the effects of climate change more apparent than in the Arctic. Sea ice loss is currently progressing at an unprecedented rate, and many long-lived Arctic species may be ill-equipped to tolerate such rapid environmental change. Ice-dependent Arctic and sub-Arctic seals, including ringed (Pusa hispida), bearded (Erignathus barbatus), and spotted (Phoca largha) seals, are important high trophic-level predators that exert top-down control within these ecosystems. Unfortunately, relatively little is known about their basic biology and physiology, leaving management agencies and conservation practitioners with an incomplete understanding of the physiological requirements and limitations of these species, and a weak ability to make predictions about the capacity of ice-dependent seals to respond to rapid environmental change. It is tough to collect physiological data from ice-dependent seals in the wild, which makes information gained from captive individuals vital to the conservation and management of these species.

Our PHOCAS program is a cooperative partnership between our team at Long Marine Laboratory in Santa Cruz, California, and the Alaska SeaLife Center in Seward, Alaska. Our aim is to work with and study the largest collection of trained ice-dependent seals in the world, in order to obtain valuable information about the biology and physiology of these unique and important species. We collect longitudinal data from the seals in our care to examine health parameters, determine short- and long-term energetic requirements, define thermal strategies and limitations, and describe the molting physiology of each species. In addition, we examine and quantify the physiological limits to diving and foraging for each species. Ultimately, data from the PHOCAS program are shared with government resource managers, native Alaskan management groups, and other scientists to expand knowledge of ice seals. Partners include researchers at University of San Francisco, University of British Columbia, Hendrix College, and Alaska Department of Fish and Game.

This project was supported by the National Oceanic and Atmospheric Administration through the Alaska Pinnipeds Program. Research activities are conducted with the approval of NOAAs Office of Protected Resources and the Ice Seal Committee, which is the tribally authorized Alaska Native co-management organization responsible for co-managing ice seals in the United States.

Synchronizing body movement to a steady beat is a behavioral ability once thought to be unique to humans. Recently, sensorimotor synchronization has been identified in a few other species, most notably parrots, who also exhibit vocal mimicry. lt has been suggested that the ability to entrain movement to rhythmic stimuli could be a byproduct of evolutionary adaptations supporting complex vocal learning. To test this hypothesis, we trained and tested sensorimotor synchronization in a mammal widely regarded as being vocally stereotypic: the California sea lion. Our sea lion subject, Ronan, has learned not only to reliably synchronize a continuous head bob to simple rhythmic sounds, but she has further demonstrated the ability to synchronize her movements with music at different tempos, respond to unexpected changes in tempo and dropped beats, and show a great deal of flexibility in her responses to patterned sounds including music. These results challenge the supposed primacy of vocal mimicry and suggest that components of ‘biomusicality’ might be more widespread in animals than previously thought.

Communication is a critical component in the social lives of marine mammals, and serves to support important life-history functions such as breeding, foraging, and parental care. Our research evaluates different communication strategies exhibited by amphibious mammals, and how these are shaped by variation in breeding systems, phylogeny, and the environment. To explore these topics we combine careful observations of natural behavior with field experiments that test the functional significance of signals to listeners. Over the past several years, our research on social communication has covered a range of topics including acoustic signaling between sea otter mothers and their dependent pups, vocal individuality and vocal and olfactory recognition between female northern elephant seals and their offspring, and active communication space of harbor seal vocalizations.

As part of this research, we maintain a long-term study to evaluate the reproductive behavior of male northern seals, who compete fiercely to monopolize access to females during the annual breeding season. We work to decode the specialized acoustic signals produced by these giant marine mammals at our field site at Año Nuevo State Reserve in central California. We carefully monitor and track focal male seals throughout their reproductive development and collect detailed information about their individual phenotype, fine-scale spatial use patterns, and pairwise competitive social interactions. This information is paired with recordings of their calls to reveal how their unusual vocal displays mediate high-stakes competitive interactions between rivals during the breeding season.

Many of our field studies deal generally with sound production and acoustic communication in pinnipeds, especially in noisy environments. However, there are many interesting aspects of sound production that are particularly difficult to study in wild animals. Our laboratory investigations involve looking at spontaneous (untrained) components of vocalizations, such as annual cycles and temporal patterns in vocal behavior, the types of sounds emitted, and the behavioral contexts in which these sounds are produced. We also address questions about how new sounds are acquired, and the role that learning and maturation play in the development of vocal communication.

We are interested in the proximal adaptations that support amphibious communication in seals, sea lions, and walruses. We tackle this research using a combination of approaches, from training animals to produce sounds while making direct physical measurements to describing vocal tract anatomy in post-mortem specimens. While we focus on the mechanisms that support sound production, we also consider non-vocal aspects of acoustic communication if different species such as flipper slaps, knocks, bells, and whistles.

We participate in a wide variety of research projects in the lab and field that aim to improve understanding of the sensory biology of marine carnivores. Topics range from measuring the sense of touch in sea otters, to examining the ability of elephant seals to distinguish their pups by smell, to evaluating the hydrodynamic reception (wake following) capabilities of harbor seals. Studying animal sensory biology is important for so many reasons, as sensory channels provide the interface through which individuals experience the world around them. As such, understanding sensory adaptations is fundamental to understanding animal behavior. Our research on sensory biology often involves training individual animals to perform extraordinary tasks. These include teaching blindfolded sea otters to distinguish textured objects with their paws and whiskers, or teaching swimming seals to track moving objects under water by feeling and following the hydrodynamic trails left behind by moving objects. Sometimes this work involves connecting anatomy and structure to specialized functions of sensory systems, as well as relating sensory inputs to higher-level aspects of cognitive processing.

Our program is perhaps best known for creative approaches to studying the cognitive abilities of marine mammals. Such research has been ongoing with trained sea lions at Long Marine Laboratory for more than 30 years. This field of research is concerned with how information gathered from different sensory systems is used by animals in decision-making, problem solving, learning, and memory. Our work in this area has spanned studies of artificial sign language comprehension, short- and long-term memory, discrimination learning, associative learning, and concept formation. Many of our studies of sea lion cognition have emphasized 'equivalence' classification, or the ability to recognize relationships between stimuli that are not based on similar features, but rather, on similar function or through connections with shared associates. This cognitive skill is shared by humans, sea lions, and some birds and mammals, and is an important topic of study among human and animal psychologists.

We also study aspects of cognition for practical reasons, as illustrated by our research concerning the effects of domoic acid exposure on sea lions and other marine life. We partner with wildlife scientists at The Marine Mammal Center to conduct research that reveals how exposure to harmful environmental neurotoxins affects both brain and behavior in free-ranging animals throughout development.