Conventional and sonar-based cameras
A number of camera-based approaches can potentially be adopted to provide information to assist platypus survey or monitoring:
Camera traps
These consist of a camera that is connected to (and triggered by) a sensor that detects animal movement and/or body warmth. To reduce the likelihood that an animal is startled when it’s photographed, many camera traps feature a noise-dampening housing. Those designed for nocturnal use may also use invisible (or less visible) wavelengths of light to illuminate images in the dark. They may also feature wireless transmission so images can be downloaded in real time and at a considerable distance from the camera. However, the practical use of land-based camera traps to identify platypus activity is limited by the fact that these animals spend little time out of the water and have a notably low profile when swimming on the water surface (though see photo below of a platypus on a log, taken by a camera trap meant to survey turtles). The highly insulating nature of platypus fur also means that the animals produce a relatively weak thermal signature even in cold water.
Time-lapse photography
Time-lapse cameras can be set up to monitor the amount of platypus activity at a given site for long periods of time (several days or even longer) before having to recharge or change batteries. Some models only work during the day, but others will work both diurnally and nocturnally (using infrared illumination in the dark). There is typically great flexibility in how often photos are recorded, ranging from intervals of 1 second up to many hours. Some models can also automatically convert photo images to a video file to assist their review. In practice, an ongoing platypus monitoring study in Tasmania has found that these animals can be reliably detected by using a camera to capture a frame every 5 or 10 seconds and then reviewing the images in a video format where one second of video footage equates to one minute of time lapse photos (12 or 6 frames). The image below provides a sense for the size of area that can be monitored effectively during daylight hours (note the platypus swimming near the fern at the left end of the pool).
Underwater cameras and video equipment
Underwater infrared camera systems that have been developed to assist with nocturnal fish research have a limited range of detection even in clear water (e.g. Chidami et al. 2007). Alternatively, it’s now possible to purchase video equipment that uses sound waves instead of light waves to create underwater images. This technology copes well with darkness and high turbidity and registers images over a far greater distance than is possible with conventional video gear. The downside is that it’s quite expensive to install, especially if numerous sites are to be monitored simultaneously.
Photos courtesy of Jesse Miller (above); Simon Roberts (below)
Literature cited
Chidami, S., Guenard, G., and Amyot, M. (2007). Underwater infrared video system for behavioural studies in lakes. Limnology and Oceanography: Methods 5, 371-378.