DOI: 10.5061/dryad.c59zw3rmt
title: Assessing cooper’s hawk (<em>Astur cooperii</em>) and sharp-shinned hawk (<em>Accipiter striatus</em>) prey size and species composition using citizen science data

description: Despite being common and widespread, the diets of Astur cooperii (Cooper’s
 Hawk) and Accipiter striatus (Sharp-shinned Hawk) have been poorly
 studied. Although some dietary datasets indicate both feed heavily on
 birds, most studies have focused on nest site or bird feeder observations,
 thus precluding comprehensive assessments of the species’ diets. Recently,
 increased popularity in citizen science programs like iNaturalist and
 eBird have allowed an unprecedented glimpse into the ecology of both
 species that may allow dietary analyses. Herein, we used iNaturalist, a
 photograph-vouchered citizen science platform, to perform an assessment of
 Astur cooperii and Accipiter striatus diets, examining patterns of prey
 size and species preferences for each predator. We hypothesized that both
 species would feed primarily on birds, however, we suspected some mammals
 might also be selected for. Across &gt;70,000 raptor observations, we
 found 4,206 (6.79% of records) and 619 (4.75% of records) predation events
 for Astur cooperii and Accipiter striatus, respectively. After accounting
 for spatial heterogeneity in observation data, we found Astur cooperii
 selected for Columbiformes, small Galliformes, Colaptes auratus (Northern
 Flicker), and invasive Passeriformes, with their preferred prey item
 matching their most observed prey item, C. livia (Rock Pigeon). Despite
 their proclivity for avian prey, Astur cooperii also fed on mammals,
 selecting heavily for Rattus norvegicus (Norway rats). The smaller-bodied
 Accipiter striatus preferred small Passeriformes, though Columbiformes
 were also selected for. Both species exhibited bimodal prey size
 selection, likely driven by differential use of Columbiformes and other
 prey items. Collectively, these data support the hypothesis that Astur
 cooperii and Accipiter striatus are avian specialists, despite Astur
 cooperii’s regular predation on small mammals.
description: In August, 2023, we downloaded all research-grade records of
 <em>Astur cooperii</em> and <em>Accipiter
 striatus</em> from inaturalist.org using the iNaturalist online data
 download tool. We then visually reviewed each record to remove any
 misidentifications/duplicate records and to determine the presence or
 absence of prey within the photograph/series of photographs. Only prey
 seen in physical contact with the <em>Astur
 cooperii</em>/<em>Accipiter striatus</em> was counted,
 to remove uncertainty on the source of the prey item (Figure 1). If a
 record contained multiple photographs, all were reviewed.
 Observed prey were identified to the lowest possible taxonomic
 group, with birds identified first by the corresponding author, then
 shared with several other PhD-level ornithologists to confirm identities.
 Mammals were preliminarily identified by corresponding author and
 confirmed by a PhD-level mammalogist who studies North American mammal
 diversity and ecology. All reptiles were identified by a PhD-level
 herpetologist who studies North American reptile diversity. For avian
 prey, some individuals could not be identified to the species level
 (<em>e.g.</em>, if silhouetted or blurry), but could be
 assigned to a coarse size class. For such records, we categorized avian
 prey items into “small” (≤ 50g), “medium” (51g – 174g), and “large” (≥
 175g) classifications. We did not conduct a similar size class assessment
 with mammals or reptiles because, with many poor quality images of those
 taxa, we found it unclear whether we could see the entire prey item or
 just a portion of the prey item (<em>e.g</em>., a mass of
 muscle with hair would clearly be of mammalian origin but unclear whether
 it was intact or from a larger carcass). Any instances of obvious
 scavenging, in particular, mesocarnivores like <em>Felis
 domesticus</em> (domestic cat), <em>Procyon lotor</em>
 (common raccoon) , and <em>Didelphis virginiana</em> (Virginia
 opossum) , were assumed to be scavenged and, thus, removed from
 analyses. <em>Weight
 assignments</em> Central to our analysis of prey
 weights was the development of a “prey weight database”. We initiated our
 prey weight database by generating a list of all species-level
 identifications of prey items (prey that could not be identified to
 species [<em>e.g.</em>, “<em>Sciurus</em> sp.”]
 were not included in the weight analyses, save for birds with size class
 identities; discussed below). For each species, we obtained a “minimum”
 and “maximum” weight using Pyle (2022; for birds), Animal Diversity Web
 (animaldiversity.org), or other published scientific literature found via
 Google Scholar. For birds of unknown species assigned to a prey weight
 class, it was assigned a body weight, for analytical purposes, by first
 assigning it a semi-random “pseudo-species” identity and its weight was
 generated using that identity. The pseudo-species was assigned by
 selecting either a random bird of the same size class (small, medium, or
 large) from within 10 km of the predation event, or, if no other records
 occurred within 10km, the closest prey item’s species identity within the
 same size class. For all predation events involving birds (including
 individuals with pseudo-species identification), mammals, and reptiles
 identified to species, we assigned each a weight based on the minimum and
 maximum weights derived for that species from the literature. For each
 such record, we assigned the prey item a weight by sampling one value from
 a normal distribution where the mean was the midpoint between the minimum
 and maximum weight and the minimum weight was -2 standard deviations and
 the maximum weight was +2 standard deviations. We performed this using the
 <em>rnorm</em> function in base R (R Core Team
 2024). <em>Weight analyses- spatial
 balancing</em> Because iNaturalist data, like
 most citizen science data, are heavily biased in space around urban
 centers (Dimson & Gillespie 2023), we corrected for this by
 thinning the data used for weight summary in a spatially balanced manner
 that effectively down-weighted records from locations with high densities
 of records and up-weighted more isolated records. Specifically, we used
 the <em>terra</em> package in R to map the coordinates of all
 <em>Astur cooperii</em>/<em>Accipiter
 striatus</em> predation observations (Hijmans 2025, R Core Team
 2024). We then created a 10km moving window across the United States,
 selecting one predation event per 10km square, regardless of the density
 of records within. This created a more spatially balanced distribution of
 prey weights for each species across the United States. We then repeated
 this process one hundred times to generate uncertainty associated with our
 sampling procedure. <em>Prey selection
 ratios</em> Finally, to estimate selection ratios
 for birds used by <em>Astur cooperii</em> and
 <em>Accipiter striatus</em>, we used the
 <em>gbif</em> package in R to extract every research-grade
 iNaturalist observation for birds, mammals, and reptiles in the United
 States from the GBIF database (Chamberlain & Boettiger 2017,
 Chamberlain et al. 2025). Each <em>Astur cooperii</em> and
 <em>Accipiter striatus</em> predation record with known prey
 species identity was plotted, and a “background” sample of 1000 random
 GBIF observations respective to each prey class
 (<em>i.e.</em>, 1000 random birds for each avian predation,
 1000 mammals for each mammalian predation, etc.) were selected from within
 a 25km buffer of each point. These samples served as prey that would be
 “available” to hawks at each predation point from which we calculated the
 proportion of each species in the background data
 (<em>m</em>). This “available prey” analysis was repeated 1000
 times, and the mean proportion of each species in the <em>Astur
 cooperii</em> / <em>Accipiter striatus</em> prey base
 (<em>n</em>) and standard deviation of n/m (σ) were
 calculated. Next, we generated selection ratios with the equation
 (<em>m</em> – <em>n</em>) / σ (Beavis &
 Mahama 2023). These selection ratios are typically interpreted as
 selection <em>for</em> a resource if that ratio is positive,
 and selection <em>against</em> a resource if negative. If zero
 or near zero, the selection ratio is interpreted as random. As an
 exploratory analysis, we regressed these selection ratios against average
 prey weights and fit a generalized additive mixed model (GAMM) to
 visualize trends within <em>Astur cooperii</em> and
 <em>Accipiter striatus</em> weight selection.
description: # Assessing cooper’s hawk (*Astur cooperii*) and sharp-shinned hawk
 (*Accipiter striatus*) prey size and species composition using citizen
 science data ## Description of the data and file structure This
 "Gibson_etal_README.txt" file was generated on 15 June 2025 by
 Darin J. McNeil Jr. GENERAL INFORMATION 1\. Title of Dataset: Assessing
 Cooper’s Hawk (Astur cooperii) and Sharp-shinned Hawk (Accipiter striatus)
 Prey Size and Species Composition Using Citizen Science Data 2\. Author
 Information ``` A. Corresponding Author Contact Information Name: Darin
 James McNeil Jr. Institution: University of Kentucky Address: 104 T.P.
 Cooper Building Lexington, KY 40546-0073 Email: darin.j.mcneil@uky.edu ```
 3\. Date of data collection (single date, range, approximate date):
 January 1980 through August 2023 4\. Geographic location of data
 collection: United States of America 5\. Information about funding sources
 that supported the collection of the data: This project was supported by
 McIntire-Stennis Capacity Grant #KY009043 SHARING/ACCESS INFORMATION 1\.
 Licenses/restrictions placed on the data: None to report 2\. Links to
 publications that cite or use the data: Authors: Gibson, W. J., E. T.
 Miller, A. M. Eling, and D. J. McNeil. In Review. Assessing Cooper’s Hawk
 (Astur cooperii) and Sharp-shinned Hawk (Accipiter striatus) Prey Size and
 Species Composition Using Citizen Science Data. 3\. Links to other
 publicly accessible locations of the data: None to report 4\.
 Links/relationships to ancillary data sets: None to report 5\. Was data
 derived from another source? yes/no ``` A. If yes, list source(s): ``` No
 6\. Recommended citation for this dataset: William, Gibson et al. (In
 Review), Title: Assessing Cooper’s Hawk (Astur cooperii) and Sharp-shinned
 Hawk (Accipiter striatus) Prey Size and Species Composition Using Citizen
 Science Data, Dryad, Dataset, [DOI] DATA & FILE OVERVIEW 1\. File
 List: File: Combined_iNatHawks_Data_15june2025.csv File:
 Combined_PreyWeightTable_15june2025.csv Description: This file contains
 all data needed to replicate analyses presented in Gibson et al., In
 Review 2\. Relationship between files, if important: Not applicable 3\.
 Additional related data collected that was not included in the current
 data package: None 4\. Are there multiple versions of the dataset? No ```
 A. If yes, name of file(s) that was updated: i. Why was the file updated?
 Not applicable ii. When was the file updated? Not applicable ```
 METHODOLOGICAL INFORMATION 1\. Description of methods used for
 collection/generation of data: See Gibson et al. (in review), Methods. 2\.
 Methods for processing the data: See Gibson et al. (in review), Methods.
 3\. Instrument- or software-specific information needed to interpret the
 data: See Gibson et al. (in review), Methods. 4\. Standards and
 calibration information, if appropriate: None to repoort 5\.
 Environmental/experimental conditions: See Gibson et al. (in review),
 Methods. 6\. Describe any quality-assurance procedures performed on the
 data: See Gibson et al. (in review), Methods. 7\. People involved with
 sample collection, processing, analysis and/or submission: See author
 contributions within manuscript. DATA-SPECIFIC INFORMATION FOR:
 Combined_iNatHawks_Data_15june2025.csv ### Files and variables #### File:
 Combined_iNatHawks_Data_20Aug2025.csv **Description: Raw data on COHA/SSHA
 depredation used for analysis**  ##### Variables * name: predator;
 description: focal species that refers to which of the two study species
 the record belongs: cooper's hawk (COHA) or sharp-shinned hawk
 (SSHA). In other words, this variable describes the predator for each
 record. * name: prey_desc; description: prey identity (common name or, for
 birds, American Ornithological Society [AOS] alpha codes [see:
 https://www.pwrc.usgs.gov/BBL/Bander_Portal/login/speclist.php]), as
 determined by Gibson et al. (if relevant). Prey description represents the
 lowest taxonomic level each prey item. "No_prey" indicates no
 evidence of prey. Value of "?" indicates that prey was present
 but no level of identification could be made. "Avian",
 "Mammalian", or "Reptilian" refer to a class-level
 identification only. For birds, we use the American Ornithological Society
 [AOS] alpha codes [see:
 https://www.pwrc.usgs.gov/BBL/Bander_Portal/login/speclist.php]. For
 example, Killdeer would be abbreviated as "KILL", Carolina
 Chickadee would be "CACH", Orange-crowned Warbler would be
 "OCWA" and Great Black-backed Gull would be "GBBG".
 For records where 2 or 3 options are all possible, they are all listed and
 partitioned by a slash. For example, a record that could be either a
 Eurasian Collared-Dove or Mourning Dove would read "ECDO/MODO".
 Some records could only be identified to genus; in that case, it would be
 depicted as (using a cottontail rabbit as an example: "*Sylvilagus*
 sp.". Some records are presumably scavenging and those are followed
 by "carcass" (e.g., white-tailed deer carcass"). Finally,
 birds that could not be identified to species but could be assigned a size
 class were listed as "large avian", "medium avian", or
 "small avian". See Methods for full description of how these
 size classes were assigned. * name: prey_Y/N; description: binary (Y/N);
 whether or not prey was detected (Y = detected, N = not detected). Records
 with "Y" are those where prey was detected in the observation.
 Records with "N" indicate that no predation event was observed
 in that record. * name: observed_on; description: date of observation
 MM/DD/YYYY format. * name: latitude; description: reported latitude of
 iNaturalist record (WGS84, decimal degrees) * name: longitude;
 description: reported longitude of iNaturalist record (WGS84, decimal
 degrees) * name: url; description: iNaturalist link to each record. ####
 File: Combined_PreyWeightTable_15june2025.csv **Description: Weight lookup
 tables for COHA/SSHA prey items**  ##### Variables * name: predator;
 description: focal species that refers to which of the two study species
 the record belongs: cooper's hawk (COHA) or sharp-shinned hawk
 (SSHA). In other words, this variable describes the predator for each
 record. * name: prey_desc; description: prey identity (scientific name),
 as determined by Gibson et al. (if relevant). Please see
 "prey_desc" for the file entitled
 "**Combined_iNatHawks_Data_20Aug2025.csv**" for interpretation
 of this variable as it is identical. * name: min_weight; description:
 lower boundary of weight (in grams) of prey item * name: max_weight;
 description: upper boundary of weight (in grams) of prey item * name:
 weight source; description: source of weight data. These were either
 scientific studies, which are cited directly, or one of three additional
 categories: ADW (Animal Diversity Web; animaldiversity.org), Birds of the
 World (http://birdsoftheworld.org/), or Pyle (Pyle, P. 2024.
 Identification Guide to North American Birds, Slate Creek Press, Forest
 Knolls, California, USA. pp., 318) * name: avian_size_class; description:
 for birds only; small, medium, or large. ## Code/software No code
 available ## Access information Other publicly accessible locations of the
 data: * iNaturalist.org Data was derived from the following sources: * See
 Methods