To record the cats’ location and activity, Alan and his team used a similar collar design to that of their lion and cheetah units. A battery under the chin of the cat weighted the collar so that the GPS aerial constantly pointed up towards the sky (and satellites!). The team aimed for a collar weight no heavier than 35 grams so that the cats would be comfortable with the unit around their neck.
The team decided that shop bought GPS technology would not be accurate enough for this study as cats spend a lot of their time running in and around areas that GPS struggles to deal with: brick buildings and dense undergrowth can cause havoc for the satellite’s signal. The GPS units that Alan and his team have developed can decipher the position of the cat to within tens of centimetres, rather than tens of metres.
The units clocked the location of the animal every 30 seconds. The GPS module time-stamped all the data. The collars also contained an accelerometer to measure the cats' activity continually and record it every two seconds to a micro SD card (the same as you would find in a camera or phone). There is also a little microcontroller (tiny computer) in the collars that monitors the accelerometer and then decides when to turn on the GPS, the sensors and the cameras. The microcontroller also monitors the GPS to put the collar and the camera to sleep when the signal is poor (meaning the cat is indoors) to save battery power. Any changes to settings were uploaded to this when the collar went in for the nightly service.
The collars used 'breakaway' safety buckles so that they would pop off if it got snagged in a hedgerow.
The BBC’s Research and Development department were assigned the task of building a lightweight camera that we could fix beneath the chin of a selected number of cats. Some GPS units had their larger batteries swapped out for smaller ones and the camera was fixed to the bottom of the GPS collar. This kept the weight to an acceptable limit.
For the first time, this allowed the scientists not only to see where the animal was, but also what it was getting up to. The battery on the camera only lasted two hours, so the RVC linked the camera to the GPS collar and then team programmed the collar GPS/sensor unit to trigger the camera’s record button only when the cat was outside (had a GPS signal) and was active (movement detected by accelerometer). This is a first for cameras of this kind. The cameras were sensitive to infrared light and shot 720p.
To ensure we were being fair to the villagers of Shamley Green, we sought consent from all of the cat’s neighbours before releasing cat cam into their village.