Trapping efficacy of invasive crows is affected by environmental factors and deployment history

Abstract

AbstractHouse crows (Corvus splendens) are considered an invasive species and are prevalent in parts of Europe, Africa, and Southeast Asia. Existing crow management measures include food limitation, habitat modification, and direct population control. The latter method provides a more immediate solution, particularly in nesting locations where crow attacks occur more frequently. Crow ladder traps are widely adopted to capture crows, but a thorough examination of the environmental conditions that optimize trapping efficacy is lacking. We assessed factors affecting crow trap efficacy in Singapore to better advise future deployment strategies of crow traps. We obtained data from 170 crow trapping operations including the identities of the contractors conducting the trapping operations, operation start date, crow density, intensity of bird feeding, various land use cover proportions, and an index to quantify the spatial‐temporal proximity to previous trapping operations. We used a spatial gamma generalized linear mixed model (GLMM) to determine the factors affecting the daily number of crows captured and a spatial binomial GLM to determine the factors affecting the probability that crows will be captured. The number of bird‐feeding incidents had a negative effect on crow trap efficacy suggesting that crows are probably less inclined to enter traps if proximate anthropogenic food abundance is high. Trapping efficacy increased if traps were placed in high crow‐density areas, likely because more crows could detect the traps. The probability of capture also declined if the traps were placed closer to prior trapping locations or with a shorter time interval from previous trapping operations. Capture rates of crows can be increased by placing traps in high crow density areas, limiting bird‐feeding incidences, and lengthening the spatial and temporal proximities to previous trapping operations. The deployment of ladder traps is a viable means to control the population of house crows and consideration of environmental conditions and trapping history can improve capture rates.