Determining predator identity from attack marks left in model caterpillars: guidelines for best practice

The use of model caterpillars to assess relative rates of predation has risen in popularity in recent years. Among the various benefits of the technique is its capacity to provide information on the identity of attackers through the impressions left in the modelling clay from which the model prey is constructed. However, there currently exists no detailed information on how to assign attack marks to particular predators. We aimed to address this gap by collating a comprehensive reference collection of the types of marks made by different predators to serve as a guide for researchers wanting to identify the predators responsible for attacks. To determine what level of resolution in identification may be considered reliable, we also tested the consistency of predator assignments made by different individuals. We found that predator identification at a coarse taxonomic level (i.e., bird, mammal, arthropod) was reasonably consistent. In contrast, when more fine-scale identification was attempted, the level of consistency and therefore also confidence in the accuracy of an identification was dramatically reduced, reflecting the difficulty of distinguishing between attacks made not only by different arthropod groups but also by differently sized birds and mammals. We recommend that identifications be made at a coarse taxonomic level and, where possible, by multiple individuals. We also suggest that our collection of images of representative attack marks from each of the coarse predator categories, and descriptions of their defining characteristics, can serve as a guide to assist with identifications and this will be complemented by a good knowledge of the locally occurring and abundant predators.