An improved global positioning system (GPS)-based animal tracking system is needed to meet quickly evolving demands of ecological research, range livestock production, and natural resource management. Commercially available tracking systems lack the data storage capacity needed to frequently collect animal location data (e.g., 15-minute intervals or less) over long-term deployment periods (e.g., 1 year or more). Some commercial systems have remote data-download capabilities, reducing the need to recapture tagged animals for data retrieval, but these systems download data via satellite (Argos), global system for mobile communications (GSM) cellular telephone, or telemetry radio frequencies. Satellite systems are excessively expensive, and GSM cellular coverage is extremely limited within the United States. Radio-based systems use narrow-band very-high- or ultra-high frequencies requiring the user to obtain frequency allocations. None of these existing systems were designed to provide continual, real-time data access. The Clark GPS Animal Tracking System (Clark ATS) was developed to meet the evolving demands of animal ethologists, ecologists, natural resource managers, and livestock producers. The Clark ATS uses memory-card technology for expandable data storage from 16 megabytes to 8 gigabytes. Remote data downloading and program uploading is accomplished using spread-spectrum radio transceivers, which do not require narrow-band radio frequency allocations. These radios also transmit, at a user-defined time interval, a real-time, GPS-location beacon to any Clark ATS base station within range (about 24 km or 15 miles line of sight). Advances incorporated into the Clark ATS make it possible to evaluate animal behavior at very fine spatial- and temporal-resolution over long periods of time. The real-time monitoring provided by this system enables researchers to accurately examine animal distribution and activity responses to acute, short-term disturbances relative to longerterm behavioral patterns. The Clark ATS also provides a huge time- and cost-savings to researchers and natural resource managers attempting to relocate a tagged animal in the field for direct observation or other operations.
Resumen
Se necesita un sistema mejorado de rastreo de animales basado en GPS para satisfacer las crecientes demandas de investigación ecológica, producción de ganado en pastizales y el manejo de los recursos naturales. Los sistemas de rastreo comerciales disponibles carecen de la capacidad de almacenaje de datos necesaria para colectar frecuentemente la localizatión del animal (por ejemplo, a intervalos de 15 minutes o menos) en un periodo largo de tiempo (un ano o mas). Algunos sistemas comerciales tienen capacidad de descargar datos a larga distancia, reduciendo la necesidad de recapturar los animales marcados para recuperar los datos, pero estos sistemas descargan los datos via satélite (Argos), a través de telefonia celular GSM o de radiofrecuencias de telemetria. Los sistemas de satélite son excesivamente caros y la cobertura de la telefonia celular GSM es extremadamente limitada dentro de Estados Unidos de America. Los sistemas basados en radio usan bandas estrechas de frecuencia VHF o UHF, requiriendo que el usuario obtenga asignaciones de frecuencia. Ninguno de los sistemas existentes fueron disenados para proveer un acceso continuo en tiempo real. El Sistema de Rastreo de Animales Clark GPS (Clark ATS) fue desarrollado para satisfacer las demandas de los etologos animal, ecologos, manejadores de recursos naturales y productores de ganado. El Clark ATS utiliza tecnologia de tarjeta de memoria para expandir la capacidad de almacenaje de datos de 16 megabytes a 8 gigabytes. La descarga remota de datos y la carga del programa se logra usando radio transcriptores de espectro amplio, que no requieren la asignacion de frecuencias de radio de banda angosta. Estos radios también transmiten, a un intervalo de tiempo definido por el usuario, en tiempo real, la localization de la baliza de GPS a cualquier base de Clark ATS dentro del rango ( aproximadamente 24 km o 15 millas en linea recta). Los avances incorporados al Clark ATS hacen posible evaluar el comportamiento animal a una résolution espacial y temporal muy fina por largos periodos de tiempo. El monitoreo en
tiempo real suministrado por este sistema permite a los investigadores examinar acertadamente la distribution de los animales y las actividades en respuesta a disturbios severos a corto plazo en relation a los patrones de comportamiento a largo plazo. El Clark ATS también proporciona grandes ahorros de tiempo y costos a los investigadores y manejadores de recursos naturales que intentan relocalizar en el campo a los animales marcados para realizar observaciones directes u otras operaciones.
Key Words: activity budgets, animal behavior, elobal positioning svstem. habitat use. real-time, telemetry tracking
INTRODUCTION
Study of animal ecology using telemetry tracking systems began in the late 1950s and early 1960s (Le Munyan et al. 1959; Eliassen 1960; Marshall et al. 1962; Cochran and Lord 1963; Mech et al. 1965) using collars or tags emitting very-high frequency (VHF) radio-signal pulses. Intensive monitoring of widely roaming animals with VHF systems, however, was costly, timeconsuming, and often posed risks to personnel safety. With the launch of the Nimbus 3 satellite (Kenward 1987) and, later, the Argos system (Fancy et al. 1988), it became possible to automatically collect and transmit location data from widely roaming or migrating animals (e.g., polar bear and caribou) using satellite communication technology (for examples, see White and Garrott 1990). The positional accuracy of these location data, however, was quite coarse (± 300 m) (Britten et al. 1999), thus negating their use for habitat-selection studies. Deployment of the NAVSTAR (Navigation Geographic Positioning System [GPS]), declared fully operational in 1995, enabled development of animal tracking systems with unprecedented positional accuracy (± 5 m) (e.g., Rodgers et al. 1996). These GPS-based tracking systems allowed evaluation of animal movement and habitat selection at very fine spatial resolution.
Despite these technological advances, however, telemetry tracking systems have not kept pace with the evolving demands of ecological research. Costs of commercial GPS tracking collars severely limit the sample size (i.e., individual animals) and statistical power that researchers have available for animal ethology and ecology studies. Commercial GPS collars also have data-storage constraints that hinder collecting location data with high-temporal frequency (e.g., every 15 minutes or less) over long deployment periods (up to 1 year or more). Consequently, intensive investigations of habitat selection, short- and long-range movements, and other animal behaviors cannot be conducted over multiple seasons or years without frequently downloading and erasing data from the collar memory. Some commercial systems have remote data-download capabilities, reducing the need to frequently recapture collared animals for data retrieval. These systems, however, download data via satellite (e.g., Schwartz and Arthur 1999), global system for mobile communications (GSM) cellular telephones, or telemetry radio frequencies (Rodgers et al. 1996). Satellite communication is very expensive. The GSM cellular coverage in the wildlands of North America is extremely limited. Radio-based systems use narrow-band VHF or ultra-high frequency (UHF) requiring the user to obtain frequency allocations, which dictate where and when these systems can be used. None of these existing systems were designed to provide the continuous, realtime data access that is often desired by ecologists, animal ethologists, and other researchers.
The objective of this research was to develop a robust GPSbased, real-time animal tracking system with the following attributes: 1 ) individual collars and mobile base-station units costing less than $1 000 each (US dollars in 2006); 2) spreadspectrum radio frequency communication between collar and base station allowing remote uploading of programming and downloading of postdifferentially correctable GPS data; 3) realtime collar tracking capabilities where GPS data describing the current location of the collar would be transmitted via spreadspectrum radio to a hand-held base station capable of receiving and displaying collar locations on a digital map; 4) collar units having a large (up to 8 gigabyte), user-expandable, on-board data storage capacity; and 5) collar components having very low power demand (mean consumption < 100 mW) and batteries with very high capacity ( 19 AH D-cells). The relatively low cost of the Clark GPS Animal Tracking System (Clark ATS) would help the user to economically deploy the system on an adequate sample size of animals, which may not have been possible using a more expensive, commercial tracking system. The capabilities of the Clark ATS would also allow the user to deploy the system for up to 3 weeks at a data-capture rate of once every minute without the need to recollect and service the collar. For longer-term deployments, the user could configure the system to acquire data at 15-minute intervals for up to 1 year without service.
MATERIALS AND METHODS
Clark GPS Animal Tracking System
The Clark ATS consists of a CPS tracking collar (Fig. 1) and a hand-held, mobile base station (Fig. 2). The tracking collar collects and stores GPS-fix information including collar location (latitude and longitude), date and time (Greenwich mean), and parameters indicating fix quality (e.g., dilution of precision and number satellites used) on a removable memory card (CompactFlash) contained within the collar. Raw satellite data (e.g., carrier phase, pseudorange, and Doppler measurements) acquired and used by the GPS receiver to calculate a GPS fix are also stored on the memory card allo