Introduction

Francesco Rovero and Fridolin Zimmermann

Camera trapping is the use of remotely triggered cameras that automatically take images and/or videos of animals or other subjects passing in front of them. This technology is changing rapidly, largely driven by market demands in the northern hemisphere, with a large proportion of the buyers being recreational hunters. The majority of commercially available camera trap models are passive infrared digital cameras triggered by an infrared sensor detecting a differential in heat and motion between the background temperature and a moving subject, such as animals, people, or even a vehicle, passing in front of them (see Chapter 2). Camera trapping as a scientific tool is widely used across the globe especially to study medium-to-large terrestrial mammals and birds, but is increasingly being also applied to other faunal targets, for example arboreal mammals (e.g. Goldingay et al. 2011), semi-aquatic mammals (e.g. river otter Lontra canadensis; Stevens et al. 2004), small mammals (e.g. Oliveira-Santos et al. 2008) and herpetofauna (e.g. Pagnucco et al. 2011). Moreover, a new type of underwater camera trap was recently designed (Williams et al. 2014) using stereo-cameras, which greatly increase the amount of quantitative data that can be extracted from images (i.e. fish size, position and orientation). The first underwater tests have successfully illustrated the potential of this technology to reveal new insights into marine organisms.

Over the last 15 years, and in particular since 2006, there has been an exponential increase in the number of published scientific studies that used camera trapping. The number of publications per year that used camera trapping increased from less than 50 during 1993–2003 to more than 200 during 2004–2014 with a relative peak of 234 in 2012 (Figure 1.1). This vast and impressive increment in the use of this tool has been accompanied by the widening of wildlife research applications, from basic faunal inventories to focal species studies, from behavioural studies to advanced, inferential studies in numerical ecology (Rovero et al. 2010; O'Connell et al. 2011; Meek et al. 2012; McCallum 2013; reviews in Rovero et al. 2013; Royle et al. 2013a).

1.1 A brief history of camera trapping

We briefly review the key steps in the advent of camera trapping since its first applications; more detailed accounts of the history of camera trapping can be found elsewhere (Sanderson and Trolle 2005; Kucera and Barrett 2011).

Camera trapping was invented in the late 1890s by George Shiras III, a lawyer and passionate naturalist who perfected a way of photographing wildlife at night with a large-format camera and a hand-operated flash. Shiras soon gained considerable acclaim for his stunning night photographs of deer and other animals (Sanderson and Trolle 2005). The first camera trap photos were taken when Shiras set up his camera so that he could take a picture remotely by pulling on a long trip-wire. Eventually, he arranged the trip-wire so that an animal triggered the camera, hence taking its own pictures. His articles in the National Geographic Magazine from 1906 to 1921 created considerable interest in wildlife photography (Shiras 1913). Subsequently, in the late 1920s, Shiras taught Frank M. Chapman (then Curator of Ornithology at the American Museum of Natural History in New York) how to use camera traps for his research work in the tropical rainforest of Barro Colorado Island in Panama. Chapman used Shiras's camera traps to capture images of the diverse and, at that time, poorly known fauna, including tapirs (Tapirus bairdii), ocelots (Leopardus pardalis) and pumas (Puma concolor). For many years, Chapman was one of the few researchers to use camera traps.

Several decades passed before researchers rediscovered camera traps as a tool, and Seydack (1984) was probably the first to use automatic camera traps to study rainforest mammals. He collected data for inventorying species as well as to estimate bushbuck abundance and identify individual leopards in Africa. Griffiths and van Schaik (1993) used camera traps to study rainforest mammals in Indonesia, and realised the potential of this method to detect species' presence and to study the behaviour, activity patterns and abundance of elusive mammals (Griffiths and van Schaik 1993; van Schaik and Griffiths 1996). Meanwhile, Karanth begun to use camera traps to identify individual tigers in Nagarahole National Park, India (Karanth 1995). His success with applying capture–recapture models to estimate population density from camera trap data (Karanth and Nichols 1998) led the way for camera trapping coupled with inferential statistics to become a powerful methodology for wildlife research.

Hunters, especially in the USA, began using camera traps in the late 1980s to search for trophy deer and other big-game species. This created a small industry resulting in an increasing range of camera trap models spanning a range of prices. At the same time, technology advanced quickly and modern camera traps soon became relatively small, waterproof plastic enclosures integrating all essential parts into one system (infrared sensor, digital camera, and flash).

1.2 Efficiency of camera trapping and advantages over other wildlife detection methods

Camera trapping is considered a non-invasive method that generally causes a minimum of disturbance to the study animals. While the presence of camera traps, the noise in the ultra-infrasonic range emitted by some models (Rovero et al. 2013; Meek et al. 2014), the smell signature of humans on the unit (Muñoz et al. 2014) and the flash (see below and Chapter 2 for details) could potentially modify the behaviour of passing animals, these potential sources of disturbance are clearly not comparable to those from faunal detection methods that require trapping and handling of animals. The majority of camera models and study types deploy LED flashes, which produce a red glow that is more or less visible to animals depending on the camera...