Everyday Practical Electronics 1998-2012 - Full Year Collection
Cris Dwellingham
Behavior is an important mechanism of evolution and it is paid for through energy expenditure. Nevertheless, field biologists can rarely observe animals for more than a fraction of their daily activities and attempts to quantify behavior for modeling ecological processes often exclude cryptic yet important behavioral events. Over the past few years, an explosion of research on remote monitoring of animal behavior using acceleration sensors has smashed the decades-old limits of observational studies. Animal-attached accelerometers measure the change in velocity of the body over time and can quantify fine-scale movements and body postures unlimited by visibility, observer bias, or the scale of space use. Pioneered more than a decade ago, application of accelerometers as a remote monitoring tool has recently surged thanks to the development of more accessible hardware and software. It has been applied to more than 120 species of animals to date. Accelerometer measurements are typically collected in three dimensions of movement at very high resolution (>10 Hz), and have so far been applied towards two main objectives. First, the patterns of accelerometer waveforms can be used to deduce specific behaviors through animal movement and body posture. Second, the variation in accelerometer waveform measurements has been shown to correlate with energy expenditure, opening up a suite of scientific questions in species notoriously difficult to observe in the wild. To date, studies of wild aquatic species outnumber wild terrestrial species and analyses of social behaviors are particularly few in number. Researchers of domestic and captive species also tend to report methodology more thoroughly than those studying species in the wild. There are substantial challenges to getting the most out of accelerometers, including validation, calibration, and the management and analysis of large quantities of data. In this review, we illustrate how accelerometers work, provide an overview of the ecological questions that have employed accelerometry, and highlight the emerging best practices for data acquisition and analysis. This tool offers a level of detail in behavioral studies of free-ranging wild animals that has previously been impossible to achieve and, across scientific disciplines, it improves understanding of the role of behavioral mechanisms in ecological and evolutionary processes.
El comportamiento es un mecanismo importante de la evolucin y que se paga a travs del gasto de energa. Sin embargo, los bilogos de campo raramente observan los animales durante ms de una fraccin de sus actividades y los intentos de cuantificar el comportamiento para el modelado de los procesos ecolgicos a menudo excluyen eventos crpticos pero importantes. En los ltimos aos se produjeron avances importantes en el monitoreo remoto del comportamiento de los animales, utilizando sensores de telemtro de aceleracin (acelermetros) que empujan los lmites tradicionales de los estudios observacionales. Acelermetros unidos a los animales miden el cambio de la velocidad del cuerpo en el tiempo y pueden cuantificar los movimientos a escala fina y posturas corporales ilimitadas por la visibilidad, el sesgo del observador, o la escala de la utilizacin del espacio. Como pionero hace ms de una dcada, la aplicacin de los acelermetros como una herramienta de monitoreo remoto ha aumentado recientemente debido al desarrollo de hardware y software ms accesibles. Se ha aplicado a ms de 120 especies de animales hasta hoy. Medidas de los acelermetros se recogen tpicamente en tres dimensiones de movimiento a muy alta resolucin (>10 Hz), y hasta ahora se han aplicado hacia dos objetivos principales. Primero, los patrones de las formas de los acelermetros de onda se pueden utilizar para deducir comportamientos especficos a travs de movimiento de los animales y la postura corporal. Segundo, se ha demonstrado que la variacin en las medidas de forma de los acelermetros de onda se ha demostrado que se correlaciona con el gasto de energa, abriendo una serie de preguntas de carcter cientfico sobre especies muy difciles de observar en la naturaleza. Hasta la fecha, los estudios de las especies acuticas silvestres superan a las especies terrestres silvestres, y los anlisis de los comportamientos sociales son muy pocos en nmero. Los investigadores de las especies domsticas y en cautiverio tienden a reportar metodologa ms completa que los que estudian las especies silvestres. Hay retos importantes para conseguir el mximo rendimiento de los acelermetros, incluyendo la validacin, calibracin y gestin y anlisis de grandes cantidades de datos. En esta revisin se ilustra cmo funciona el acelermetro, se proporciona una visin general de las investigaciones ecolgicas que han empleado los acelermetros y se destacan las mejores prcticas emergentes para la adquisicin y anlisis de datos. Esta herramienta ofrece un nivel de detalle en los estudios de comportamiento de los animales salvajes que han sido hasta ahora imposibles de alcanzar y, en todas las disciplinas cientficas, que mejora la comprensin del papel de los mecanismos de comportamiento de los procesos ecolgicos y evolutivos.
Everyday Practical Electronics 1998-2012 - Full Year Collection
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The field of biotelemetry grew out of the need to locate animals at will and observe and record their habits despite their abilities to travel rapidly and widely in inclement weather, underwater, or at night [12, 13, 15]. Locating animals in space has progressed from manual tracking of animal-borne radio- or acoustic signals to automated depth and geomagnetic loggers and satellite-based positioning systems that practically eliminate the observer effect and can now provide precise worldwide locations with few temporal or spatial constraints [11, 16]. Nevertheless, a record of animal locations or a depth profile tells where the animal was and how long it stayed there, but the behavioral context is absent and must either be inferred or demands a return to direct observation methods [17]. These issues underscore the need for remote measurement of animal behavior to reduce or eliminate the potential effects of observer presence while maintaining a high level of detail in data recording that is comparable to direct observation [18]. Over the past few years, there has been an explosion of research on remote monitoring of animal behavior using measurements of acceleration (Figure 1) [19, 20]. This tool, the accelerometer, has repeatedly circumvented many of the age-old limits of direct observation of animals in the field.
Movement is the fundamental behavioral response to both internal motivations and the external environment [13, 17]. Using accelerometers, biologists can measure the movement behavior of wild animals over biologically and ecologically significant events and periods, practically unlimited by visibility, observer bias, or geographic scale. Accelerometers can be deployed with other sensors, such as those recording location (GPS, acoustic telemetry, water depth), physiological measurements (heart rate, body temperature), and environmental variables like air temperature, light levels and magnetic heading [24, 39, 40]. Particularly when combined with other instruments, measurements of acceleration can provide a wide range of detailed information on the environmental context of animal behavior and physiology that can exceed the descriptive abilities of the human observer and deepen our knowledge even for well-known species such as domestic animals. Here, we review how accelerometers have been used to date in the study of animal behavior, including the taxonomic and research trends in the literature and we illustrate the type of data produced by this technology from instruments deployed on a variety of species. Further, we provide a summary of the currently available techniques for data calibration, management and analysis, and suggest key directions for future research.
We accessed BIOSIS Previews and ISI Web of Knowledge online and ran searches for any publication containing references to accelerometry in the title, abstract or keywords. We limited our analysis to primary research published in peer-reviewed journals and book chapters through December 2012. From those, we selected studies utilizing animal-borne sensors applied to non-human species. We assessed the resulting works for the following: i) study purpose; ii) species and whether subjects were captive/domestic or free-ranging, and aquatic or terrestrial; iii) number of acceleration axes; iv) sampling frequency utilized; v) the behavioral resolution of the resulting measurements; vi) the parameters of the accelerometer data used for analysis; vii) whether or not behavioral classification accuracy was reported (if pertinent); and viii) whether accelerometry was combined with other telemetry sensors. Results are presented as percentages; not all percentages will sum to 100 because not all categories were mutually exclusive.
More than half of all studies (62.3%) utilized 3-axis accelerometers; 90.3% of studies utilized either 2- or 3-axis accelerometers. Sampling frequencies ranged from 0.5 Hz to 10,000 Hz, with 60% of studies using one of the following most common sampling frequencies of 8, 10, 16, 32, 64 or 100 Hz. Forty-eight percent of studies collected acceleration data continuously and 13.3% collected data in discrete bursts or intervals; 38.7% of studies did not clearly report their collection method. Sixty-three percent of studies combined an accelerometer with other telemetric instruments; however, free-ranging wild species were 3 times more likely than captive wild species and 6 times more likely than domesticated species to be outfitted with telemetry devices that contained multiple sensors. The most common remote sensors used in tandem with accelerometers measured depth (35.6% of studies), travel speed (16% of studies) and temperature (14.7% of studies).
Overall dynamic body acceleration shown for a hopping and non-hopping cane toad Bufo marinus . This study was the first to use accelerometry to establish a behavioral time budget and assign energy costs to those behaviors for a non-volant terrestrial animal. Graphic reprinted with permission from [109].
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