A comparison and critique of different scat-analysis methods for determining carnivore diet

Abstract

1. For terrestrial carnivores, scat analysis is the technique most often used to determine diets. Various methods of interpreting scat-analysis data exist; however, little is known about how the choice of method affects the results. 2. We reviewed 50 scat-analysis papers to assess the range of methods currently used. Furthermore, we used a large data set from cape fox Vulpes chama and black-backed jackal Canis mesomelas scats to compare 11 scat-analysis methods. Techniques tested included five biomass calculation methods, four frequency of occurrence methods, one method that estimated volume in scats, and another that estimated mass of food items in scats. 3. Frequency of occurrence methods were used in 94% of reviewed papers, and in 50% of papers they were the sole methods used. However, we conclude that frequency of occurrence has the least ecological significance and results can be misleading. Although biomass calculations probably provide the best approximation to true diets, only 23% of reviewed papers used suitable biomass calculation methods when models were available for the study species. 4. Analysis of fox and jackal scats showed that there were significant differences among methods when calculating percent diet composition and niche breadth. Additionally, dietary overlap between species differed considerably among the methods (range of R0 = 0.29-0.79). We conclude that the choice of method can have a significant impact on the results of dietary analysis, and can lead to very different conclusions about a species' ecology. 5. The best approximation of the true diet can be obtained by using a biomass calculation model that was developed for the same species, or for a closely related species with a similar food spectrum. When no such model is available, either the volume or mass of diet components in the scats should be used. To document rare food items, frequency of occurrence data could also be given.

An Assessment of Spatial and Temporal Variation in the Diet of Cape Clawless Otters (Aonyx capensis) in Marine Environments

“…PDM is the dry mass of a prey category relative to the dry mass of the spraint. PO ranks the occurrence of various prey items, rather than indicating the relative quantities in the diet (Carss & Parkinson, 1996), often resulting in the underestimation of prey taken in large quantities (Englund, 1965;Jenkins, Walker & McCowan, 1979) but can account for rare food items leading to a better understanding of a carnivore's ecology, such as its role as an opportunist or specialist (Klare, Kamler & MacDonald, 2011). The PDM of food remains as an estimate of importance is also limiting, since it favours prey species that are made up of large amounts of indigestible material such as crustaceans, whilst prey made up mostly of soft tissue are under-represented (Somers, 2000;Emmerson & Philip, 2004).…”

Wolf diet in an agricultural landscape of north-eastern Turkey

“…Scats of uncertain origin were discarded. Despite drawbacks pointed out for scat analysis and the related prey use indices (Klare et al 2011), this methodology is helpful in preliminary surveys of carnivores' diet and is still widely used, which facilitates comparisons with results from different studies.…”

“…Remains contributing < 5% of the total scat volume were considered as traces and not accounted for utilisation rate. Utilisation indices, in particular FO, tend to underestimate the share of big prey compared to the small ones and can be misleading when prey greatly differ in size (Klare et al 2011). Therefore, we applied a biomass model to convert the equivalent number of scats in biomass and calculated the relative share of prey categories.…”

“…Therefore, we applied a biomass model to convert the equivalent number of scats in biomass and calculated the relative share of prey categories. Biomass models are sensitive to the weights of prey used during experimental feeding trials (Klare et al 2011); thus, we chose the model which would cover the range of prey weights found in our sample (Table 1). We used the equation developed by Floyd et al (1978), Y = 0.02X+0.038, where Y is the kilograms of prey per collectable scat and X is the mean prey weight (kg).…”

Impact of wolf hunting policy on moose populations in northern Minnesota

“…With consideration of scat analysis techniques identified by Klare et al (2011), researchers will also perform bi-monthly scat surveys in transects by foot, ski or snowshoe. 5…”