A variety of techniques have been developed to survey terrestrial mammal populations. The efficacy of these field techniques varies across species and environments. To select the most appropriate technique for a given situation, conservation scientists and managers require a clear knowledge of the advantages and disadvantages of each potential technique. Therefore, studies combining and comparing different sampling methods in different species and in a variety of areas are extremely valuable. In our last expedition to Sibiloi National Park (Kenya), the Global Change and Conservation team combined different monitoring terrestrial mammals’ techniques live trapping, spoor surveys and camera trap sampling-, which allowed us to document the current terrestrial mammal composition status of the area.
Live trapping is used mostly for small and medium size terrestrial mammals, but may not be suitable for species that required specialized techniques. Trapping techniques need intense effort, they are time-consuming and, in some cases, their high costs limit the size of datasets. Animal capture has the disadvantage of keeping the animal in the trap, with the potential to stress it and alter its normal activities. Many trapping options exist such as modified Hickman live traps baited with sweet potato for subterranean rodents, British Longworth traps for colder climates, Collapsible Tomahawk traps for squirrels and small carnivores, and pitfall traps for mammals under 10 g. The use of bait or not is still in debate. In our expedition, we used Sherman live traps that have become the standard foldable.
Spoor surveys are one of the oldest known methods for identifying mammal species living in an area and include direct observation and signs identification, including scats and tracks in dust, mud, sand or snow. Many studies conduct spoor transects along dirt roads with soft surfaces that register animal footprints and, by using vehicles, spoor surveys have the advantage of allowing extensive distances to be surveyed. It is difficult to determine the age of tracks, which are vulnerable to human and climatic interference and substrate differences. Aerial surveys are frequently used for estimating population densities and trends for large mammals, but this is an expensive option. In our expedition, spoor surveys were carried out along 3 km transects in different habitats -grassland, riverbed and bush-.
Camera trap sampling has become an increasingly common method for surveying carnivore populations. Camera traps use motion- and heat-sensing infrared technology to collect data on a diversity of species, in all types of weather conditions, and without the need for an observer to be present. This technique is considered as a non-invasive, where images of wildlife species are recorded with a minimal disturbance to the animals. However, recent studies suggest that the emission of light (flashlight) and sound from camera traps can be disturbing. Camera traps allow individual recognition by their unique marks, permitting estimates of density. However, the start-up costs of camera trap surveys are expensive. The camera model and how it is positioned affect the likelihood of image capture success. Camera traps may also be vulnerable to damage or theft. In our expedition, camera traps were located along transects and in opportunistic locations.
Check the On the Right Track? publication to learn more about comparing camera trap sampling and spoor surveys.