DOI: 10.5061/dryad.37pvmcvnm
title: Data from: Predation probabilities and functional responses: How piscivorous waterbirds respond to pulses in fish abundance

description: 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 (&gt;645,000 tagged and &gt;32,000
 recovered steelhead) to quantify weekly predation probabilities and
 functional responses across waterbird species, colonies, and years. Weekly
 predation probabilities were highly variable, ranging from 0.01–0.30 at
 tern colonies, 0.01–0.20 at cormorant colonies, and 0.03–0.13 at gull
 colonies. Per capita predation probabilities were an order of magnitude
 higher at inland tern and cormorant colonies relative to estuary colonies
 of the same species. Terns displayed Type II functional responses across
 colonies and years, where predation probabilities peaked at low steelhead
 abundances and declined as steelhead abundance increased (i.e., predator
 swamping). Cormorants nesting at the large estuary colony (several
 thousand birds) displayed a Type III functional response, but cormorants
 nesting at the smaller inland colony (several hundred birds) displayed a
 Type II response. Consumption probabilities of steelhead by gulls remained
 consistent across a large range of steelhead availability, suggesting a
 Type I or a Type III functional response, but a lack of colony abundance
 data prevented quantifying functional responses. The level of tern
 predation combined with Type II functional responses indicate possible
 population-level impacts that could destabilize small or declining prey
 populations. Conversely, the apparent Type III functional responses of
 gulls and estuary nesting cormorants are indicative of prey switching
 behaviors targeted at periods of high steelhead abundance. Our results
 illustrate the complexity of predator-prey interactions and the importance
 of quantifying predator- and location-specific functional responses when
 predicting the efficacy of management strategies to enhance prey
 populations.
description: Data files and R scripts refelct the final formatted data to run
 the predation probablity and functional response models presented in:
 Hostetter, NJ, Q Payton, DD Roby, K Collis, and AF Evans. Predation
 probabilities and functional responses: How piscivorous waterbirds respond
 to pulses in fish abundance. PIT tag detection data
 were retrieved from the PIT Tag Information System (PTAGIS), a regional
 salmonid tag database maintained by the Pacific States Marine Fisheries
 Commission, during January 2020 (PSMFC 2020). Detailed
 information on PIT tag recovery data are in the associated manuscript and
 Evans et al. (2012; 2019) and Hostetter et al. (2015).
 <strong>Literature Cited</strong>
 Evans, A. F., N. J. Hostetter, D. D. Roby, K. Collis, D. E.
 Lyons, B. P. Sandford, R. D. Ledgerwood, and S. Sebring. 2012. Systemwide
 evaluation of avian predation on juvenile salmonids from the Columbia
 River based on recoveries of passive integrated transponder tags.
 Transactions of the American Fisheries Society 141:975–989.
 Evans, A. F., Q. Payton, B. M. Cramer, K. Collis, N. J.
 Hostetter, D. D. Roby, and C. Dotson. 2019. Cumulative effects of avian
 predation on Upper Columbia River steelhead. Transactions of the American
 Fisheries Society 148:896–913. Hostetter, N. J., A. F.
 Evans, B. M. Cramer, K. Collis, D. E. Lyons, and D. D. Roby. 2015.
 Quantifying avian predation on fish populations: integrating
 predator-specific deposition probabilities in tag recovery studies.
 Transactions of the American Fisheries Society 144:410–422.
 PSMFC (Pacific States Marine Fisheries Commission). 2020. PIT Tag
 Information System (PTAGIS): A regional database.
 www.ptagis.org.
description: Contact NJ Hostetter for additional data or usage requests.