CARGO ESTRUCTURAL : TÉCNICO EN TRIBUTACION I

Tracking is the biotelemetry technique conventionally used to investigate ecological dynamics (e.g. home range, habitat use, population estimation, migration, mortality, social interactions, etc.) in wildlife (Kays et al. 2015). Knowledge of these dynamics informs conservation strategies in threatened and endangered species or management solutions that foster a compatible coexistence between ranging animals and humans. For one example, wild animals may cross interurban roads and highways that cut their pathways; consequently, they may collide with vehicles risking their life and that of human drivers. Animal tracking systems allow researchers to map the animals’ usual passages and accordingly build ecological corridors, such as tunnels and bridges, that allow the animals to pass beneath or above roads (Maletzke et al. 2005).

More recently, tracking has been used within the management of farm animals (e.g. to locate and reduce losses among grazing herds (de Weerd et al. 2015)), working animals (e.g. to monitor the work of search and rescue dogs (Komori et al. 2015)) and domestic animals (e.g. to investigate roaming habits of outdoor cats (Hervías et al. 2014)).

The three main technologies used for tracking animals (Figure 2.3) include radio telemetry, such as Very High Frequency (VHF), and satellite systems, such as the Advanced Research and Global Observation Satellite (ARGOS) and Global Positioning Systems (GPS).

Figure 2.3: Graphic representation of the three main technologies used for tracking animals. VHF tags convey radio signals picked up with an antenna; position is obtained through triangulation. ARGOS devices send Doppler Shift signals to the satellites which transmit the signal back to a user computer. GPS loggers receive signals from the satellites and store them into their internal memory; loggers need to be retrieved in order to download the data into a computer (© 2016 www.sirtrack.co.nz).

Each of these technologies has functional advantages and disadvantages. Albeit an older technology, VHF has been favoured for ecological studies particularly with small animals. The tags require little energy and therefore run on small batteries, which makes them very small and light (12 x 5 x 2 mm, 0.19 grams for 5 days lifespan6 _{– in: (Habib et al. 2014)), as}

well as inexpensive.

However, whilst VHF tags are cheap and light, various practical and procedural drawbacks limit their employment. For example, locating individuals in their environments is a labour intensive and costly process, which requires the presence in the field of an operator for long hours to control a receiving antenna. This also alerts animals, which may flee or hide for a long time in response to human disturbance. These induced behaviours are recorded, adding biases during data acquisition. For example, individuals may go beyond their habitual territory to avoid human presence, resulting in an unreliably wider home range. Additionally, the VHF detection distance is limited, which precludes its use with wide- ranging species. The range depends on the shape and length of the transmitting aerial, which is a device component attached to the animal. Antennae are an element of obstruction for wearers if mounted externally to the devices encase (e.g. whip type); they can alter animals’ movements and activities, adding further biases. Additionally, the radio signal is vulnerable to variations in topography (which diffract wave propagation), vegetation or weather, which limits the effectiveness of VHF in mountainous or wooded environments. In contrast, ARGOS does not suffer from signal vulnerability. Theoretically, it enables global tracking in almost real-time, sending acquired information directly to the user’s computer. For this reason, it is particularly used with marine wildlife (Costa et al. 2010), which is arduous to track manually.

However, while the technology virtually eliminates labour costs and operator disturbance, the tags are expensive and using the satellite service incurs fees. Moreover, the location accuracy is poor compared to VHF and GPS (Habib et al. 2014) and compared to VHF tags the devices are heavier so they cannot be used on small animals.

GPS is another global tracking system, but in contrast to ARGOS it is also very accurate (circa 5 m radius) under open sky (Rempel and Rodgers 1997). Therefore, it is suitable for studying with precision the movements of wide ranging and migratory animals. It has also become popular for tracking domestic companion animals (von Watzdorf and Michahelles 2010).

However, since the signal is undetectable from under-water and underground, and is inaccurate in thick vegetation, GPS is not suitable for tracking marine, burrowing or dense woodland animals, except if and when they surface. This problem has partially been solved by combining traditional GPSs with the Fastloc® location technology, which is a signal snapshot receiver able to acquire a satellite wave in less than 60ms (Rutz and Hays 2009). However, although the technology virtually incurs no fieldwork costs, the devices are expensive. They are also power-hungry which increases the weight and size of the devices, making them unsuitable for small animals, and also shortens battery life, making them unsuitable to study wild animals for long periods.

Conversely to ARGOS tracking, GPS is a receiving technology that stores the inputs transmitted by the satellite into the internal memory of the GPS unit. In order to download the data, end users (e.g. researchers, pet carers, farmers) have to either retrieve the device by recapturing the animal or add data transmitters to the GPS element. Both these measures for recovering the data have disadvantages. On the one hand, chasing and recapturing wild animals is highly stressful for them, impinging on their psychological and physiological wellbeing (Wilson and McMahon 2006). On the other hand, transferring data wirelessly from the GPS module to a receiving station requires additional transmitting components which increase both weight and extra battery usage of the GPS unit (Habib et al. 2014). Nevertheless, remote data retrieval standards and services such as the Global System for Mobile communications (GSM) and the General Packet Radio Service (GPRS) are regularly integrated in the current generation of GPS units since the benefit of not-recapturing overcomes the extra load and battery drainage drawbacks, while enabling accessory functions, such access to data in real-time and immediate response to targeted animal behaviours. For example, cell-phone technology can be used to access an animal’s location by sending an SMS (Short Message Service), or to set ‘virtual fences’ which notify users when tracked individuals cross a pre-defined border (e.g. pets who move far from home, or wildlife who trespasses human settlements) (Kays et al. 2015).

The high heterogeneity in shape, size, behaviour and environment of different animal species makes the development of one-size-fits-all tracking device currently unfeasible (Markham and Wilkinson 2008). Therefore, all the technological solutions developed over the past 60 years are in use today and choices about their deployment are made based on specific contextual and technical constraints such as size, environment, mobility and sensitivity of the animal, energy consumption and harvesting, tag costs, data retrieval, and

signal capture and accuracy. This implies three necessary requirements for biotelemetry devices: they must adapt to animals, deliver usable and low-cost data to humans, and reliably work for the time and place they are employed.

To optimally meet such requirements, hybrid solutions, combining various wireless and mobile phone networks with radio and satellite tracking systems, have been developed through collaborations between biologists and computer engineers. For example, the ZebraNet project delivered GPS collars equipped with wireless transceivers (i.e. a combined device that both transmits and receives radio signals) which work as a peer-to-peer network to monitor zebras in open lands (Juang et al. 2002); the Electronic Shepherd system integrated GPS receivers, UHF (Ultra High Frequency) radio transceivers, and GPRS modems for tracking high-pasture sheep (Thorstensen et al. 2004); the EcoLocate system fused together GPS and VHF technologies to create a wireless network for monitoring mammals of a wide size-spectrum in the Savannah (Markham and Wilkinson 2008). On the pet-consumer market we are witnessing the same trend. At the time of writing, various manufacturers provide GPS, GSM, GPRS, GloNaSS (Global Navigation Satellite System) applications, or various combinations of them, for devices specifically designed to be used on pets. Many examples of such products can be found online (Kippy.eu, G-Paws.com, Tractive.com, Pawtrax.co.uk, Pawtrack.com).

However, on the whole, both single and hybrid solutions are devised paying great attention to technological capabilities and user’s data-gathering needs, while merely adapting the tags to target animals in terms of miniaturisation. Shrinking the device size is certainly a priority for animal biotelemetrists who seek to gather good data from unswayed animals of any size (Kays et al. 2015); indeed, tag conspicuousness is a primary factor that burdens animal carriers and limits the applicability of the technology to medium-to-large-sized animals. However, the challenge of designing adequate biotelemetry technologies concerns more aspects of the animals’ life and needs than solely their size.