Owl pellets: a more effective alternative to conventional trapping for broad‐scale studies of small mammal communities

Abstract

Summary Small mammal community composition is almost universally estimated from conventional trapping, which is logistically difficult to scale up for landscape‐level assessments. Owl pellets may be a more effective alternative for measuring small mammal community composition over large geographic areas due to the relative ease and low cost of field collections. However, owl pellets may introduce sampling biases that differ from those associated with conventional trapping. A thorough comparison to conventional traps is required before owl pellets can be widely adopted as an alternative research tool for small mammal studies. We conducted a literature review of owl diet‐prey availability studies to: (i) compare small mammal community composition between owl pellets and trapping when the two methods were used simultaneously and (ii) assess the influence of owl genus and habitat type on community composition estimated by these two methods. We used data from 27 published studies, which allowed for 32 comparisons between owl pellets and trapping conducted simultaneously. These studies included 15 owl species from five common genera from different major habitats. Rarefied estimates showed that owls consistently sampled identical or higher species richness compared to conventional trapping. Richness estimates rarefied to the lowest sample size per study were not statistically identical (μΔrichness = 0·20 ± 0·09 SE, P = 0·30); on average, 0·95 ± 0·13 SE additional species were identified from pellets compared to trapping. Measures of species dominance and evenness estimated from both methods were statistically identical (μΔ1‐D = 0·02 ± 0·03 SE; μΔPIE = 0·004 ± 0·04 SE). Species lists, relative species composition and species rank‐order abundance were in moderate agreement between sampling methods (Jaccard = 0·62 ± 0·04 SE; Bray–Curtis = 0·53 ± 0·04 SE; Spearman rho = 0·41 ± 0·07 SE). Linear regression and AIC model selection showed that the performance of pellets versus traps did not differ based on owl genus or habitat type. Small mammal community composition estimated via pellets was better represented compared to estimates from conventional trapping. Composition metrics from the two methods were consistent and not affected by owl genera or habitat type. Thus, owls are an effective alternative for landscape‐level assessments of small mammal communities.