emote-sensing techniques have transformed ecological research by providing both spatial and temporal perspectives on ecological phenomena that would otherwise be difficult to study (eg Kerr and Ostrovsky 2003; Running et al. 2004; Vierling et al. 2008) . In particular, a strong focus has been placed on the use of data obtained from spaceborne remote-sensing instruments because these provide regional-to global-scale observations and repeat timeseries sampling of ecological indicators (eg Gould 2000). The main limitation of most of the research-focused satellite missions is the mismatch between the pixel resolution of many regional-extent sensors (eg Landsat [spatial resolution of ~30 m] to the Moderate Resolution Imaging Spectroradiometer [spatial resolution of ~1 km]), the revisit period (eg 18 days for Landsat), and the scale of many ecological processes. Indeed, data provided by these platforms are often "too general to meet regional or local objectives" in ecology (Wulder et al. 2004) . To address this limitation, a range of new (largely commercially operated) satellite sensors have become operational over the past decade, offering data at finer than 10-m spatial resolution with more responsive capabilities (eg Quickbird, IKONOS, GeoEye-1, OrbView-3, WorldView-2). Such data are useful for ecological studies (Fretwell et al. 2012) , but there remain three operational constraints: (1) a high cost per scene; (2) suitable repeat times are often only possible if oblique view angles are used, distorting geometric and radiometric pixel properties; and (3) cloud contamination, which can obscure features of interest (Loarie et al. 2007) . Imaging sensors on board civilian aircraft platforms may also be used; these can provide more scale-appropriate data for fine-scale ecological studies, including data from light detection and ranging (LiDAR) sensors (Vierling et al. 2008) . In theory, these surveys can be made on demand, but in practice data acquisition is costly, meaning that regular time-series monitoring is operationally constrained. A new method for fine-scale remote sensing is now emerging that could address all of these operational issues and thus potentially revolutionize spatial ecology and environmental science. Unmanned aerial vehicles (UAVs) are lightweight, low-cost aircraft platforms operated from the ground that can carry imaging or non-imaging payloads. UAVs offer ecologists a promising route to responsive, timely, and cost-effective monitoring of environmental phenomena at spatial and temporal resolutions that are appropriate to the scales of many ecologically relevant variables. Emerging from a military background, there are now a growing number of civilian agencies and organizations that have recognized the possible applications of UAVs, including the National Oceanic and Atmospheric Administration, which states that UAVs "have the potential to efficiently and safely bridge critical information gaps" in data-sparse locations "and advance understanding of key processes in Earth sys- In a nutshell: REVIEWS REVIEWS REVIEWS Lightweight unmanned aerial vehicles will revolutionize spatial ecology • Ecologists require data collected at appropriate spatial and temporal resolutions for a range of studies • Unmanned aerial vehicles (UAVs) can carry various imaging or non-imaging payloads to provide spatial datasets for a variety of end users • The benefits of UAVs are that (1) survey revisit periods (ie the number of repeat flights over a designated site) can be user controlled, (2) low-altitude flight allows sensors to observe the ground from more proximal positions and potentially collect finer spatial resolution data, and (3) operating costs are low • We review current approaches to UAV deployment, summarize their demonstrated and potential applications, and suggest new ways in which UAVs could be used to underpin novel, scale-appropriate environmental science research
In this research area, Anderson and Gaston REF highlight the applicability of UAVs in the field of ecology, emphasizing that the spatial and temporal resolutions of the data obtained by traditional methods often do not adapt well to the requirements of local ecological research.
Lightweight unmanned aerial vehicles will revolutionize spatial ecology
Frontiers in Ecology and the Environment
Biology