WRL referenceM02 D04
ModuleM02Ecological Survey Techniques
Data setD04Camera trapping to assess large mammal populations in Amazonia
______
Background to the research:
Monitoring the population sizes of mammals is crucial to understanding the effects of natural and man-made environmental changes and to ensure conservation strategies are working effectively. For mammals that are large, gregarious, conspicuous or that favour open habitats, population sizes can be estimated from direct observations. A common surveying technique is the line transect, which involves an observer moving along a pre-determined route through the study area, and recording the distances at which the animals of interest are seen. Software is then used to estimate population densities from this data, based on the rate at which sightings decrease with distance from the transect. To count rare, shy or elusive mammals or mammals that are predominantly active in the evenings (crepuscular) or at night (nocturnal) requires less direct means, such as the use of camera traps. Essentially, camera traps are devices with sensors that activate a camera to take a photograph when an animal is present. Remote photography using camera traps is becoming increasingly popular for surveying such animals as they do not disturb the creatures they are filming, they collect data under a range of environmental conditions, they are relatively easy to use and the permanent record of each sighting enables more accurate species identification.
The Amazon basin has some of the highest levels of biodiversity in the world and the Pacaya-Samiria Nature Reserve in Peru is no exception, with over 100 mammal species present. These include arboreal primates, for example howler monkeys, saddle-backed tamarins and brown capuchins, and diverse terrestrial and arboreal mammals such as jaguar, puma, opossums, armadillos, sloths, tapirs and peccaries. One of the greatest challenges faced by many of these mammals is the dramatic and prolonged annual flooding that occurs as a result of seasonal rainfall changes over the Andes. As the water levels rise so the amount of available land decreases, condensing terrestrial animals into smaller areas. For herbivores this means there is both less vegetation present and also greater competition for resources, though there may be a lag before seeing the effects of these circumstances reflected in the population size. Whilst carnivores are also concentrated into a reduced area, they benefit from the tighter assemblages of their prey.
Red brocket deer and ocelots are just two of the terrestrial mammals found in the Pacaya-Samiria Nature Reserve whose populations are being monitored using camera trap networks.
Red brocket deer, Mazama americana (left) are forest ungulates found throughout the lowlands of the Amazon basin. They are strictly herbivorous, browsing on leaves, twigs and flowers, grazing on grasses and foraging on fallen fruits and seeds. Most active at dawn and dusk, the red brocket deer are solitary animals that inhabit dense forest undergrowth. As potential prey for large cats such as jaguar and puma, red brocket deer are also wary creatures and so are rarely seen by observers walking along transects.
The ocelot, Leopardus pardalis(right), is a predominantly nocturnal solitary predator which often spends the daylight hours asleep out of sight in trees, again making direct observations difficult. Similar in appearance to a domestic cat but roughly twice the size, ocelot use vision, hearing and scent to hunt their prey, which consists mainly of small mammals such as rodents but that can also include birds, lizards, frogs, turtles, crabs, and fish.
The water levels of the rivers of the Peruvian Amazon, which includes the Samiria River, drop to a mean low of 17.54m in November and reach a mean high of 27.77m in June, meaning the height of the rivers fluctuate by more than 10 metres over the course of an average year. The Samiria River varies annually to a similar extent, and when water levels are at their highest only 2% of land in the Pacaya-Samiria National Reserve are not flooded. In July of 2009, however, these waters rose an extra 2m (the nearby Marañón River reached a height of 29.77m), reducing the land available to terrestrial mammals to only the very highest points of land that were few and far between.
Based on numbers of camera trap sightings, this study aims to investigate how the populations of these two animals were affected following the unprecedented high water levels during the flooded season on the reserve in 2009.
To further see how camera traps can be used to understand densities of secretive animals such as big cats, see the accompanying paper by Silve et al. (2004) on estimating population sizes of jaguar in different regions of South America.
Operation Wallacea | |
These data were gathered from the Opwall Peru expedition:Copyright: these resources are the sole property of Operation Wallacea although they may be used freely for educational purposes within the classroom or for internal examinations. Further use will require permission which can be gained by email.