COMMENTARY Does this photo make my range look big? A. Dobson & K. Nowak EEB, Eno Hall, Princeton University, Princeton, NJ, USA Correspondence Andy Dobson, EEB, Eno Hall, Princeton University, Princeton, NJ 08540, USA. Email: rachel.wheatley@wiley.com doi:10.1111/j.1469-1795.2010.00381.x We have a friend with a wonderful garden in rural Appa- lachia. He’s both fascinated by nature and a confirmed camera addict. He decided to set some cameras at different points around his ‘back-yard’ along the edge of Black Roshannon State Park in Central Pennsylvania. He was amazed by what the cameras detected: bob-cats, coyotes, black bears, as well as a huge abundance of turkeys and white-tailed deer that he’d seen but only partially realized were so common (Fig. 1). Similar things happened to Mark Hixon at the University of Oregon when he put underwater remote cameras on coral reefs. The technology to take photographs underwater has improved hugely over the last few years, but the catch with photography is that the photographer always has an influ- ence on who’s in the picture. This becomes truly apparent when the camera is left on the edge of a reef and set to automatically take pictures when something new ‘interrupts’ its field of view, or breaks an infra-red beam. In the case of coral reefs, predators suddenly appear in great abundance, massively underlining the impression you get when scuba diving that something large and predatory is watching you! Mark Hixon’s photos provide strong evidence that a sig- nificant abundance and diversity of large piscivorous fish is still present in areas where they are not often sighted. Could this rapidly developing and increasingly available technology be used for quantifying the diversity and abun- dance of rare mammals in tropical forests? And can it do so on large enough spatial scales to produce indices of abun- dance that meet the requirements for long-term monitoring of biodiversity (Balmford, Bennum et al., 2005; Balmford, Crane et al., 2005; Dobson, 2005). The article by O’Brien and colleagues on page 335 of this issue illustrates that camera traps may provide an incredibly powerful new tool for monitoring biological diversity – the wildlife picture index. They show that networks of camera traps can be readily coordinated using a number of subtle statistical tools to provide non-invasive and highly balanced methods for long-term monitoring of rare species in tropical forests. A number of other recent studies provide increasing support for the use of remote cameras as major tools for monitoring biodiversity, they illustrate the power of these methods to detect and quantify the communities of verte- brate species that other techniques often fail to detect. Heat- activated camera traps have been widely used to inventory the occurrence and conservation status of elusive and threatened mammals (Rovero & De Luca, 2007; Tobler, Carrillo-Percastegui et al., 2008) and to study their activity and resource partitioning (Bowkett, Rovero & Marshall, 2008; Tobler, Carrillo-Percastegui & Powell, 2009). They have been used to estimate density using mark–recapture models for species with distinguishable individuals (e.g. Silveira et al., 2009). When individuals cannot be distin- guished, trapping rates have recently been calibrated with independent indices of animal abundance (Rowcliffe et al., 2008; Rovero & Marshall, 2009). The use of camera traps is non-invasive, cost-effective, facilitates the standardization of survey methods across sites and enables the rapid assess- ment of biodiversity in remote areas. Moreover, having images of rare species makes it easier to communicate the importance of sites and set conservation priorities. A significant number of rare and secretive carnivores have effectively been rediscovered with camera traps: in Iran, the largest remaining group of Asiatic cheetahs was photographed in 2005; in the Amazon rainforest, the short- eared dog or zorro, the only species in genus Atelocynus has recently been caught on camera after its re-discovery in 1990; in the Udzungwa Mountain forests of Tanzania the rare Jackson’s mongoose, African’s least known carnivore, has been photographed marking a first record of the species in Tanzania (De Luca & Rovero, 2006). The Tanzania Mammal Atlas Project has combined intensive camera trapping surveys with sighting data to generate checklists of species for Tanzania’s major national parks, to update species distribution maps, and to develop national conservation action plans for its mammals (e.g. Pettorelli et al., 2009). One of the more notable findings include a tree pangolin photographed in Minziro, one of the three patches of forest representing the Guinea-Congo biome in Tanzania, potentially a Sokoke dog mongoose (known primarily from Sokoke Forest north of Mombasa, Animal Conservation 13 (2010) 347–349 c  2010 The Authors. Journal compilation c  2010 The Zoological Society of London 347 Animal Conservation. Print ISSN 1367-9430