DOI: 10.5061/dryad.jm63xsjn9
title: Data from: Congregations of rodent-eating birds during flood irrigation of crops exploit novel prey pulses and potentially provide pest control services

description: In California’s Central Valley, we have observed large congregations of
 rodent-eating birds, including wading birds, raptors, and Corvids- hunting
 for rodent prey during flood irrigation of alfalfa fields. A pilot study
 in 9 fields revealed a mean of 23.7 rodent-eating birds, and a maximum of
 102 birds, hunting simultaneously in a field. We observed a total of 293
 rodent prey captures in 570 minutes of monitoring and calculated a mean of
 1.03 rodent prey captures per hour of avian hunting effort. We believe
 these initial observations provide insights into the responses of
 rodent-eating birds to an intensive farming practice that echoes natural
 fluctuations in surface water. We propose four testable hypotheses for
 others exploring the role of irrigation practices for carnivorous birds-
  1) Rodent-eating birds use social and environmental cues to
 exploit prey during short-term flood irrigation events; 2) Rodents make up
 a larger proportion of the diet of Ardeidae species in regions that use
 short-duration flood irrigation compared to regions where this practice is
 not used, and flood irrigated fields may therefore sustain carnivorous
 bird populations in areas where natural wetlands are scarce; 3) Birds
 provide significant rodent pest control services within flooded alfalfa
 fields; and, 4) Nocturnal predators respond to short-term flood irrigation
 events in a similar pattern as diurnal birds.
description: We identified 9 alfalfa fields that utilized flood irrigation in
 Yolo County, in California’s Central Valley. We visited fields during
 irrigation and visited each site 1-4 times in May-July in 2017 or 2018. 
 Each visit consisted of a 30-minute period split into six consecutive
 5-minute observation intervals. Within each interval, we counted any
 ‘rodent-eating bird’: species that include rodent prey in their diet,
 including raptors, wading birds, and corvids. We observed foraging of
 birds present in fields and counted all rodents consumed by birds in the
 same time interval. Rodent species were not discerned between, however
 fossorial rodents commonly impacted by flood irrigation in this region are
 Botta’s pocket gopher  and California vole.  Only rodents that were
 sighted being consumed were counted. Wading birds held prey items in their
 beaks prior to swallowing them, whereas birds of prey including
 <em>B. swainsoni</em> generally appeared to consume prey items
 by holding them on the ground and tearing pieces off to eat. We therefore
 believe we have underestimated prey consumption rates by raptors in
 particular.
description: # Data for Congregations of rodent-eating birds during flood irrigation of
 crops exploit novel prey pulses and potentially provide pest control
 services
 [https://doi.org/10.5061/dryad.jm63xsjn9](https://doi.org/10.5061/dryad.jm63xsjn9) ## Description of the data and file structure ### Files and variables #### File: Data\_for\_Kross\_et\_al\_2025\_Ornithological\_Applications.xlsx **Description:**  ##### Variables * Data includes the site ID, the date of the observations, the temperature (C), percent sky obscured by clouds, wind on a 0-5 scale, the height of the crop, the start and end time of each 5-minute observation period, and then a column for each of the rodent-eating bird species we commonly observed and a column for the number of rodent prey items that were observed caught by each bird species within the 5 minute interval. We use 4-letter codes to represent the bird species. There are also columns for the total number of rodent-eating birds observed, the total number of prey items, and calculations for the number of rodent prey 'per bird hour' for the main species we observed. See the publication for further explanation of this calculation. Missing data: n/a. The column names and descriptions are as follows: site_rename_compress: Unique identifier for each site name, starting with year. Letters used across years do not represent the same sites date: Date observations were made Temperature: Temperature in C Cloud Cover: Percent of sky covered in clouds Wind: Following a 0-5 Beaufort scale Crop Height: Estimate in inches of the height of the crop in the flooded field. 0 represents recently mowed crop, not 0 plants. Start_Time: Start time of each observation interval End_Time: End time of each observation interval GREG: Number of Great Egrets observed GREGpreyitems:Number of rodent prey seen captured by Great Egrets GBHE: Number of Great Blue Herons observed GBHEpreyitems: Number of rodent prey seen captured by Great Blue Herons BCNH: Number of Black-crowned Night Herons observed BCNHpreyitems: Number of rodent prey seen captured by Black-crowned Night Herons SWHA: Number of Swainson's Hawks observed SWHApreyitems:Number of rodent prey seen captured by Swainson's Hawks RTHA: Number of Red-tailed Hawks observed RTHApreyitems: Number of rodent prey seen captured by Red-tailed Hawks Raven: Number of Common Raven observed Ravenpreyitems: Number of rodent prey seen captured by Common Raven Crow: Number of American Crows observed Crowpreyitems:Number of rodent prey seen captured by American Crows Other_canivores: Number of other carnivorous birds observed other_prey_total: Number of rodent prey seen captured by other carnivorous birds Total_no_birds: The sum of all rodent-eating birds observed in the 5-minute period Total_prey: The sum of all prey observed being caught in the 5-minute period Captures.bird.hour: Calculated based on the total number of birds x 5 minutes to calculate the number of hours of cumulative hunting effort were observed in the 5 minute observation period and using the sum of prey captured in that time. GREG.captures.indiv: Calculated based on the total number of Great Egrets x 5 minutes to calculate the number of hours of cumulative Great Egret hunting effort were observed in the 5 minute observation period and using the sum of prey captured by Great Egret in that time. GBHE.captures.indiv:Calculated based on the total number of Great Blue Heron x 5 minutes to calculate the number of hours of cumulative Great Blue Heron hunting effort were observed in the 5 minute observation period and using the sum of prey captured by Great Blue Heron in that time. SWHA.captures.indiv: Calculated based on the total number of Swainson's Hawks x 5 minutes to calculate the number of hours of cumulative Swainson's Hawkshunting effort were observed in the 5 minute observation period and using the sum of prey captured by Swainson's Hawks in that time. BCNH.captures.indiv: Calculated based on the total number of Black-crowned Night Heron x 5 minutes to calculate the number of hours of cumulative Black-crowned Night Heron hunting effort were observed in the 5 minute observation period and using the sum of prey captured by Black-crowned Night Heron in that time.