Data from: Congregations of rodent-eating birds during flood irrigation of crops exploit novel prey pulses and potentially provide pest control services
Data files
Mar 03, 2025 version files 30.04 KB
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Data_for_Kross_et_al_2025_Ornithological_Applications.xlsx
25.68 KB
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README.md
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Abstract
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.
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
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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.
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 B. swainsoni 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.