Predation probabilities and functional responses: How piscivorous waterbirds respond to pulses in fish abundance

How predators respond to changes in prey abundance (i.e. functional responses) is foundational to consumer-resource interactions, predator-prey dynamics, and the stability of predator-prey systems. Predation by piscivorous waterbirds on out-migrating juvenile steelhead trout (Oncorhynchus mykiss) is considered a factor affecting the recovery of multiple Endangered Species Act-listed steelhead populations in the Columbia River basin. Waterbird functional responses, however, may vary by predator species and location, with important implications to predator management strategies. We used a 13-year dataset on waterbird abundance across seven breeding colonies (three Caspian tern [Hydroprogne caspia], two double-crested cormorant [Nannopterum auritum], and two California and ring-billed gull [Larus californicus and L. delawarensis] colonies) and steelhead tag-recovery data (>645,000 tagged and >32,000 recovered steelhead) to quantify weekly predation probabilities and functional respon...