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Through your binoculars you spot a pair of hippo nostrils on the surface of the river. You hold your breath for a few seconds before they vanish from sight. As a field biologist, you may only catch a glimpse of the animal you study. Yet consumer electronic advancements are changing how researchers observe animals in the wild. The technology that guides you to a cup of coffee in an unfamiliar city is changing field biology. New sensors are revealing the secret lives of animals that were once too difficult to study: small mammals hidden in burrows, large mammals too dangerous to approach, and birds winging across the sky. Researchers are now discovering how these creatures move, where they spend their time, and what they do to survive.
Animal behavior is often fascinating—and unexpected. As animals hunt for food, avoid predators, and find mates, they employ a wide range of strategies. Biologists have traditionally described animal behavior by observing wild animals while they ate, slept, hunted, and played. Much of what we know about animal behavior comes from these long hours of patient observation, including the well-known work of Dr. Jane Goodall, who directly observed and made accounts of chimpanzee behavior in Africa. Mating dances among birds and hunting strategies of predators like wolves and polar bears have been described from years of difficult and sometimes dangerous fieldwork, often in remote areas. The knowledge of animal behavior gained from all these observations helps us avoid dangerous human-animal interactions, and to design conservation strategies for those species at risk.
However, some animals are incredibly difficult to observe. They may be small, remote, skittish, or active in terrain that makes direct observation challenging or impossible. Technological advances in telemetry (remote measurement) are enabling biologists to advance our understanding of important behaviors in wildlife. Radio telemetry, Global Positioning Systems (GPS), and accelerometry have played significant roles in expanding our knowledge of what animals do when we cannot see them.
Radio telemetry uses radio frequencies to locate animals in the wild. Individual animals are fitted with tags that emit a unique radio frequency. Once the animal is released, a researcher trying to locate that animal points a radio receiver out across the landscape in hopes of receiving a signal. Detection requires a line of sight between the tag and the radio receiver. Upon receiving a signal, the researcher knows the approximate location of that animal at a given moment in time.
More recently, wildlife applications of GPS technology have enhanced our knowledge of where animals go because GPS enables ecologists to measure repeated locations of specific animals over time. Researchers outfit an animal with a GPS tag, which periodically logs locations at a set time interval—say, every 30 seconds. That information may be collected either by remote download or by physically retrieving the tag. The locations may then be analyzed to determine the habitat preferences of the animal, its proximity to other features on the landscape, and potential travel routes between high areas of use. By outfitting animals with GPS tags, researchers learn how an animal moves through the landscape without ever catching a glimpse.
Success using GPS tracking technology with wildlife laid the groundwork for experiments with other sensors. Accelerometry (see Toolbox), a more nascent technology, now adds a new dimension to questions about wild animal behavior. GPS tracking can tell a scientist where an animal spends its time; accelerometers create the opportunity to learn what an animal is doing while out of sight. Right now, you probably have such a sensor on your person. Most smartphones contain an accelerometer, allowing the visual projection to rotate as you change the orientation of the screen. Wildlife accelerometers are as clever as those of your average smartphone because they are multi-axial. They can sense and record acceleration along two or three axes, which tells researchers much more about what the animal is doing.
Each movement produces a different magnitude and direction of acceleration, and sometimes matching acceleration measurements to a particular behavior can create signatures of behavior. Suppose you are sitting in a chair. You then get up and start walking to get a cup of coffee. The accelerometer tracks the change in acceleration from your behavior of sitting to that of walking and someone monitoring those changes would know that sitting and walking are two different behaviors. You then walk across the room, reach down, and start loading wood into your fireplace. This produces a different set of accelerations, providing yet another signature. With just this information, far-off researchers could figure out how much of your day you spend sitting versus walking versus moving wood. In wildlife biology accelerometry has astonishing consequences, allowing researchers to know what an animal is doing even when it is out of sight.
Dr. Wayne Getz, professor of wildlife biology in the UC Berkeley Department of Environmental Science, Policy, and Management, aims to understand how an animal moves and expends energy throughout the day. In animal behavior studies over the last 15 years, Getz and colleagues have employed radio telemetry tags, GPS location devices, and accelerometers to understand the movements and habits of large animals. “When we studied buffalo in Kruger National Park in Africa, we relied on radio telemetry, then in our elephant research we started using GPS collars, and now we are using a combination of GPS and accelerometers.” This technological progression advances the questions biologists address—they now learn not only whether an animal is present or absent in an area, but also connect these locations with specific behaviors. The combination of accelerometer and location data provides a powerful opportunity to describe which locations are important for animals to acquire food, find mates, and raise young.
Getz and his graduate students continue to use GPS tracking technology with accelerometry to link specific animal behaviors with locations. One key to this ongoing research is the continued advancement of accelerometer technology. In particular, the increase in GPS and accelerometry use in ecological research follows decreasing device size—a trend largely driven by the growing efficiency of batteries. Whereas a smartphone can be charged at home, at the office, and even in the car, once the tracking or sensor device is on an animal it cannot be easily recharged. As Getz puts it, “accelerometery sensors are small and the batteries have always been larger. That leaves you with some tough decisions. The longer you have the sensor gathering data, the more power you need, and the more the battery will weigh. Advances in communications technology and energy efficiency of tags have made these smaller, but it is still a series of very difficult decisions and tradeoffs.”
Keeping tabs on vanishing vultures
Most recently Getz focused on the griffon vulture, a bird found in southern Europe, northern Africa, and parts of Asia. Griffon vulture populations have dramatically declined in all these regions; therefore, understanding what vultures need to survive and what may aid their recovery is timely for conservation biologists. Griffon vultures are large birds, with a seven-to-nine foot wingspan, who rely on finding carcasses from the air. Because they fly such great distances, they are difficult to track with direct observation, and researchers do not know why their numbers are shrinking.
The impetus of declining populations and the difficulty of visually observing such a wide-ranging bird made vultures an intriguing candidate for accelerometry. Getz, along with his colleagues Dr. Ran Nathan and Dr. Orr Spiegel, fitted griffon vultures from northern Israel with accelerometers and GPS locators (measuring longitude, latitude, and elevation). Tagged griffon vultures were then observed in both zoos and in the wild to match certain behavior categories—standing, eating, and flying—with signature acceleration profiles. Moreover, signature accelerations were determined between vultures that were flapping their wings and those that were soaring. These behavioral signatures gave the researchers a view of where vultures go, how they spend their energy, and how they associate with the seasonal conditions in these areas. The seasonality of behaviors such as breeding, as well as the geographic space used for these behaviors, may be important for vulture conservation plans in these regions.
Getz and his colleagues also discovered some puzzling vulture behavior. Vultures fly longer and farther during the summer, when they can ride thermals and soar without flapping their wings. Understanding what drives these extensive flights across the landscape may be the key for successful vulture management. While these long, energy intensive forays may seem odd, such excursions may be important to vulture social structure or for long-term knowledge of likely locations of food sources. Getz states “what we really want to understand is vulture conservation. What cues do they use to find carcasses, what is the function of these long forays, and how important is it for them to range wildly?” With vulture populations threatened throughout their range, this information may help conservation biologists understand what natural resources vultures need in order for their populations to recover.
Can chipmunks keep cool?
Alpine hikers may catch sight of mountain chipmunks scurrying around fallen logs and behind rocks, but these creatures are small and difficult to follow by eye. What does a day in the life of a mountain-dwelling chipmunk look like? Where do these animals spend their energy? Will they be able to alter these behaviors to cope with climate change? Chipmunks are one of several alpine animals that may be threatened by changes in climate. Recent research by Dr. Craig Moritz and others at the Museum of Vertebrate Zoology at UC Berkeley found that some small mammals living in the mountains have shifted their range to higher elevations over the past century, possibly compensating for impacts of climate change.
The researchers described these changes by using traps to re-survey areas originally surveyed 100 years ago by UC Berkeley researcher Dr. Joseph Grinnell and his colleagues in the Sierra Nevada. Alpine ecosystems are considered high risk for climate change-driven loss of biodiversity, because alpine animals and plants cannot indefinitely move up the mountain in search of cooler temperatures. Whether chipmunks are physiologically capable of coping with climate change, or have the ability to change their behavior to mitigate its consequences, remains to be seen and may shed light on this question for other animals.
Advances in telemetry are allowing a team of UC Berkeley graduate students to investigate these small alpine mammals. Rachel Walsh, a biology graduate student, has spent the last few summers using radio telemetry to better understand the habitats used by two species of chipmunk from the Grinnell re-survey study: the Alpine chipmunk (Tamias alpinus) and the Lodgepole chipmunk (Tamias speciosus). Moritz and his colleagues discovered that the two species associate with the landscape differently—the Alpine chipmunk spends the majority of its time at the highest elevations, a range that has contracted upwards over the past century. In contrast, the Lodgepole chipmunk has a broad range, spanning various elevations, and that range has remained consistent during the past century of climate change. These observations provided an opportunity to study behavior in these two closely related species to better explain different responses to shifting climates. But chipmunks posed a challenge because they are difficult to watch; they are fast, tiny, and spend time in small hiding places. Using radio telemetry, Walsh better described the habitats used by the chipmunks on a small scale, and laid the groundwork for additional use of tracking technologies.
A better understanding of chipmunk behavior is one key to understanding the risks of climate change for these species. It may be that the Lodgepole chipmunk can remain at lower elevations by limiting energy expenditures during the heat of the day, or simply using energy in a different way. This is the target of ongoing research by Tali Hammond, another biology graduate student at UC Berkeley. Hammond continues to look for behavioral differences between the two chipmunk species to better understand their shifts in range. Does one chipmunk species spend its day differently than the other and does that have consequences for survival?
Large radio telemetry collars were commercially available when Walsh used them for her chipmunk research. Hammond, however, wanted to experiment with a sensor that was not yet available: accelerometers that could be attached to chipmunks. Creating a sensor and battery suitable for a small animal is challenging, not least due to size constraints. With an animal this small, they needed a device that weighed about a nickel so that it would not inhibit the chipmunk’s ability to follow its usual activities. Hammond and Walsh partnered with Dwight Springthorpe, a graduate student in integrative biology, to develop a chipmunk-scale sensor. Springthorpe, who studies biomechanics in animals, has worked on adapting technology and tag design for wildlife studies in birds and insects. Springthorpe’s biomechanics background has proved an excellent fit for bringing technology to chipmunk research. Together, these researchers have found clever solutions to fit the size and lifestyle of chipmunks. “Battery life is always an issue, but so are the unique needs of an individual experiment,” Springthorpe remarks.
“There are many tradeoffs when you design these tags,” says Springthorpe. “Size, weight, durability, are some of the considerations, but so is the frequency of sampling.” Tags can save battery power by going into sleep mode in between recording information. The tradeoff is whether your goal is a lot of information over a short time window, or evenly spaced, infrequent sampling over a longer period. As battery and sensor technology improved, animal tracking devices became smaller and smaller, and Springthorpe built a tiny enough tag to work.
Hammond continues to work with Springthorpe to test these lightweight accelerometers in the field. First, Hammond used Springthorpe’s accelerometer tags to look for predictable behavior signatures in captive chipmunks. “We fitted chipmunks with accelerometers and filmed them in a large, semi-natural arena, where the accelerometers transmitted recordings to a computer-base station, giving us concurrent observations and accelerometer data” describes Hammond. Hammond categorized behaviors in captive animals into high impact, low impact, and resting. “High impact” includes running and jumping, “low impact” includes eating and nesting, and “resting” includes sleeping and remaining still.
A fourth member of this research team, Taylor Berg-Kirkpatrick, a graduate student in the computer science department, used this data to create a computer program that could translate raw accelerometer data into behavioral categories. The next step involves applying these studies to the field—in the Sierra Nevadas. While fieldwork complicates the process, Hammond is excited about its potential. “We showed that accelerometer data can be used to relatively reliably and remotely determine four broad categories of behavior in these two species without ever actually observing behavior directly,” she notes.
Hungry, hungry hippos
On the opposite side of the spectrum in size and ferocity, hippos–like chipmunks–are difficult to study. Hippos are dangerous, causing more human deaths than any other animal in Africa. Hippos are also primarily active at night, and consequently much of their behavior remains unknown. Tristan Nuñez, a graduate student in the UC Berkeley Department of Environmental Science, Policy, and Management, studies hippos in Kenya. While they are an iconic species recognizable to children and adults alike, Nuñez notes that “it is surprising, but we do not know much basic information about hippos, such as how they use the landscape for eating and resting.” Hippos are difficult to study because they spend much of the daytime under water in large rivers. This is where they sleep, play, mate, and give birth. All these behaviors are invisible to researchers. As Nuñez puts it, “if you are trying to observe daytime behavior of hippos, you may just see the occasional set of nostrils surfacing in the water.”
Using methods derived from the study of marine mammals, Nuñez has used GPS technology to begin tracking hippo movements. Yet even these tracks are fraught with challenges. Once hippos are underwater, GPS technology, which requires a satellite connection that cannot occur through more than a few feet of water, does not work well. Therefore, Nuñez must interpret GPS tracks with gaps—a hippo may enter the river at one point, and then exit at a later time with no GPS points recorded in the interim. This means that we know very little about what they are doing.
The use of accelerometers takes this research a step further. Nuñez is planning to characterize accelerometry signatures of hippo behavior by observing hippos in zoos and, where possible, in the wild. By matching observations to accelerometer data, he may figure out what the hippos are doing underwater, and understand how that impacts their survival. Moreover, a better understanding of hippo behavior may improve human safety for those people who live near hippos. Knowledge of the habitat hippos prefer when they are on land at night may enable wildlife managers to find ways to mitigate human-hippo interactions. When a human encounters a hippo at night, both humans and hippos can be killed: the human by a charging hippo or the hippo by a human gun shot. A more sophisticated understanding of where hippos locate along the rivers may allow humans to avoid many future encounters.
Knowledge of hippo behavior is also important to the ecology of rivers because hippos have a large impact on how rivers flow. The movement of hippos in and around rivers actually changes the river channel shape. Hippos create ruts and pools along the river shoreline that serve as habitat for other river species. Additionally, hippos are voracious eaters. When asked about how much they eat, Nuñez smiles. “The estimates are that each night hippos eat fifty kilograms of grass.” All those nutrients in the grass have to go somewhere. Hippos may be transporting these nutrients to the river by eating at night and defecating in the water during the day. The location of their foraging, and the ultimate fate of nutrients they excrete, whether it be on land or in the river, have ecological consequences for other animals, and may be part of a natural cycle of river fertilization. Sensors and the tags that hold them are central to this effort, as Nuñez sums up. “High-powered electronics give us an opportunity to monitor animals in a way we could not before, which will allow us to better understand the impacts large animals have and inform how we interact with them and create conservation policies.”
Accelerating conservation with accelerometers
With future sensor developments, new possibilities will emerge for monitoring animals in the wild. Chipmunks, vultures, and hippos represent just three of many challenging study species, and these research projects are just the tip of the iceberg. Much of the hidden life of wild animals remains swathed in mystery. Telemetry has transformed into a tool to discover links between behavior, location, and time, even when animals are out of sight. Armed with ever-cleverer gadgets, field biologists are identifying the geographic areas and seasons critical to finding mates, nursing young, acquiring food, and other activities important to animal survival. Conservation strategies for both species and ecosystems rely on understanding what animals need to survive and whether they can alter their behavior to cope with changes to their environment. Though many field biologists will always have their notebooks and binoculars, technological advances are giving scientists increasingly sophisticated tools to observe and understand the workings of the natural world.
Featured Image: Credit: Holly Williams