REVIEW A practical guide to avoid giving up on giving-up densities Miguel A. Bedoya-Perez & Alexandra J. R. Carthey & Valentina S. A. Mella & Clare McArthur & Peter B. Banks Received: 28 April 2013 /Revised: 11 July 2013 /Accepted: 13 July 2013 /Published online: 1 August 2013 # Springer-Verlag Berlin Heidelberg 2013 Abstract The giving-up density (GUD) framework provides a powerful experimental approach with a strong theoretical underpinning to quantify foraging outcomes in heterogeneous landscapes. Since its inception, the GUD approach has been applied successfully to a vast range of foraging species and foraging scenarios. However, its application is not simple, as anyone who has tried to use it for the first time might attest. Limitations of the technique were noted at its conception, yet only the artificiality of the patches, the appropriateness of the food resource, and the possibility of multiple visiting foragers were identified. Here we show the current uses of GUD and outline the practical benefits as well as the often overlooked limitations of the technique. We define seven major points that need to be addressed when applying this methodology: (1) the curvilinearity between harvest rate and energy, (2) the ener- getic state of the forager, (3) the effect of group foraging, (4) food quality and substrate properties, (5) the predictability of the patch, (6) behavioral traits of the forager, and (7) nontarget species. We also suggest how GUD experiments can be en- hanced by incorporating complementary methods (such as cameras) to better understand the foraging processes involved in the GUD itself. We conclude that the benefits of using GUD outweigh the costs, but that its limitations should not be ignored. Incorporating new methods when using GUD can potentially offer novel and important insights into the study of foraging behavior. Keywords Foraging . Giving-up density . Landscape of fear . Methodological limitations . Practical assumptions . Supplementary approaches Introduction By the time Ernst Haeckel (1873) proposed “Ökologie” as the name of a new, emerging branch of science—modern ecology —foraging was already an established and widely used term that described the process of looking for food, defining where and what an animal chooses to eat. However, the idea of foraging as a mechanism for maximizing fitness was not proposed until the 1960s (Emlen 1966; MacArthur and Pianka 1966). This was followed by the development of opti- mal foraging theory (OFT), and a myriad of mathematical models have since been constructed to help understand this theory (Stephens and Krebs 1986; Stephens et al. 2007). Early models describing how OFT worked were mostly theoretical (Charnov 1976; Pyke et al. 1977), although some approached foraging from a more practical, yet qualitative perspective (Hay and Fuller 1981). In 1988, Joel S. Brown described an elegant experimental and mathematical approach to quantita- tively measure an animal's foraging decisions in the wild based on patch characteristics, using giving-up density (GUD). The GUD framework is underpinned by an extension of the mar- ginal value theorem (Charnov 1976), relying on the existence of food patches as a depletable food source that foragers exploit differentially in order to maximize fitness. Therefore, the amount of food that foragers leave in a patch (i.e., the GUD) reflects the perceived cost of foraging at that patch, such that a lower GUD indicates a lower net cost. According to this framework, in a depletable patch where harvest rate (H) decreases as more food is con- sumed over time, the forager should quit the patch when the benefits of harvesting no longer outweigh the costs. This framework incorporates costs associated with predation risk (P), searching and processing (i.e., handling and digesting) resources from that patch as well as thermoregulatory costs (C) and missed opportu- nities elsewhere (MOC). The concept (Brown 1988) is expressed as: Communicated by P. M. Kappeler M. A. Bedoya-Perez (*) : A. J. R. Carthey : V. S. A. Mella : C. McArthur : P. B. Banks School of Biological Sciences, The University of Sydney, Camperdown, NSW 2006, Australia e-mail: miguel.bedoyaperez@sydney.edu.au Behav Ecol Sociobiol (2013) 67:1541–1553 DOI 10.1007/s00265-013-1609-3