With reference to Figure 4.1, given the availability of resources (e.g. animal experts, ethograms, etc.) that allow a designer to understand the species of interest (a), the values and principles of wearability (b1 and b2) would help the designer to identify the set of animal variables (d) that inform the wearer needs relevant for the interactors (c). Principles and values also would help to individuate device features, components and attachments (e) that need to be (re)designed to achieve wearability in relation to the set of variables identified. The combination of wearer needs and device design establish the wearability requirements. Wearability and usability requirements, along with system capabilities (f1, f2, f3), need to be traded-off (g) in order to identify possible designs that provide optimal wearability and functionality. The WCF focuses on what is ideal for the wearer; user requirements and system capabilities are analysed to elicit trade-offs, but they are informed by other frameworks (e.g. user- or system-centred). Ideally, the WCF is applied as follow in the next section.
4.3.1 How to operationalise the framework: An example
The following simplified example illustrates how the framework can be operationalised to systematically establish requirements for the design of wearer-centred tags.
Relations among the WCF components
Consider a wildlife project that makes use of trackers to monitor a North-American population of red foxes20. Biotelemetrists aim at using devices that do not affect the
individuals being monitored. Wearer-centred designers are involved in the design of the tags. As they use the WCF as a guiding tool, they recognise foxes as the wearer interactors and start applying the principles one at a time. Designers firstly focus on the principle of
sensory imperceptibility for the sense of hearing and aim at designing an aurally
imperceptible tag. They consult an animal expert to acquire the relevant information regarding the wearer and the wearer’s significant others. The WCF assists them in considering who the prey and predators of foxes are, which hearing capabilities are involved (e.g. which frequencies are audible by the species of interest), which critical and delicate activities may be influenced by the tag (e.g. by interfering with mating calls, alerting and dispersing prey, or disrupting ambushes), and which environments have to be considered (e.g. type of habitat that propagates sound). This assists in determining which needs the interactors have. Next, electronic components of the device that may be responsible of frequency emission are individuated. Wearability requirements for a
device are established in relation to the components that need to be (re)designed and in relation to the sensory characteristics of foxes and of their significant others.
Establishing wearability requirements
The possibility that a biotelemetry tag might emit ultrasounds audible to animals has been demonstrated by studies on bat dataloggers, which revealed the emission of ultrasonic bands in the measure of circa 33,000 Hz (Willis et al. 2009). In this respect, the WCF prompts designers to assess the presence of detectable radiation from the device in relation with the aural capabilities of all the animal species that are likely to be involved or affected (i.e. instrumented animals plus their significant others within the geographical context and distribution area in question). Experts are questioned about the matter. In this simplification, foxes have an audiogram within the approximate range of 51-48,000 Hz (Malkemper et al. 2015) (for comparison: humans’ audiogram is commonly 20-20,000 Hz). The audiogram of foxes’ significant others varies: their typical prey, mice, have an aural sensitivity of circa 1,000-91,000 Hz21; their potential (but not regular)
predators/competitors living in the studied area, coyotes22, are likely to have an aural
sensitivity of circa 67-45,000 Hz (although their exact hearing range is not known, it is likely similar to that of canids such as dogs21). This means that in order to meet the hearing
requirement (consistent with the principle of sensory imperceptibility), a device used on foxes should not emit auditory signals within the frequencies of 51-91,000 Hz, which is the combined minimum and maximum frequency hearable by at least one of the three species. Figure 4.2 summarises the abovementioned requirement analysis for hearing: if the wearer, or the individuals interacting with him, are able to hear particular frequencies that may be produced by a device, the principle of sensory imperceptibility prescribes that the designer should avoid design solutions that involve acoustic signals, or technologies that may produce a vibration, in the range audible by the wearer and their significant others. In this example, this means that sound actuators that produce frequencies from 51 Hz to 91 kHz should be avoided.
21 Strain GM (2003) How well do dogs and other animals hear? Web page (accessed 7 November 2018) - https://www.lsu.edu/deafness/HearingRange.html.
22 https://www.smithsonianmag.com/science-nature/foxes-and-coyotes-are-natural-enemies-or-are-they- 180968424/.
Figure 4.2: Foxes listen frequencies from 51 Hz to 48 kHz, while their typical prey, mice, hear ultrasounds from 1 kHz to 91 kHz. Coyotes’ range is in between. The device, in order to be aurally imperceptible, should not produce frequency in the range of 51 Hz and 91 kHz which are the minimum audible by a fox and the maximum by a mouse.
Managing trade-offs
If the envisaged tag does not produce any noise within the 51-91.000 Hz range, then the hearing requirements related to the sensory imperceptibility principle are fulfilled. On the contrary, if the technology the designers propose to use generates a resonance, the device design should be revised and technologies that do not produce ground noise in the 51- 91,000 Hz span should be used (or designed) instead. Should this not be possible due to current technological limitations, trade-offs should be considered following a scale of importance, where the importance of a requirement should be determined by the severity of the expected impact produced by the electronic tag on the wearer if said requirement was not met. To continue with this example, as mentioned above, coyotes are accidental predators/competitors of North-American foxes, while mice are regular fox quarry. Thus, the predatory impact of coyotes on vulpines is less significant than fox hunting failure on mice, which can lead to starvation, especially because mice rely on their very highly sensitive hearing system to escape predators, whereas the hunting behaviour of coyotes on foxes is principally driven by smell (Mazis 2008). Therefore, starvation being a more likely impact to occur than being attacked by coyotes and hearing being a primary sense used by mice to defeat predation, designers need to prioritise the hearing capabilities of mice and make sure that any acoustic emissions from the device fall outside the mice’s hearing range, where total sound avoidance is not possible.
The same assessment process should be carried out for each known significant other (e.g. mice are not the only prey foxes rely upon) and for all of the relevant variables associated
with the biological and environmental characteristics of the animals in question. More specifically, these are related with the sensory, physiological, morphological and psychological characteristics of animals, their physical and social environment, their living conditions, daily activities, behaviours, and movements (List 1 in appendix 2).