Data from: Feeding en route: Prey availability and traits influence prey selection by an avian predator on migration

# Prey availability and traits influence prey selection by a sexually dimorphic avian predator on migration During animal migration, transient communities of taxa at all trophic levels co-occur over space and time. The interactions between predators and prey along migration corridors are ecologically and evolutionarily significant. However, these interactions remain understudied in terrestrial systems and warrant further investigations using novel approaches. We investigated the predator-prey interactions between a migrating avivorous predator and ephemeral avian prey community in the fall migration season. We tested for associations between avian traits and prey selection and hypothesized that prey traits (*i.e.*, relative size, flocking behavior, habitat, migration tendency, and availability) would influence prey selection by a sexually dimorphic raptor on migration. To document prey consumption, we swabbed trace prey DNA from beaks and talons of migrating Sharp-shinned Hawks (*Accipiter striatus*; n=588). We determined prey availability in the transient avian community by extracting weekly abundance indices from eBird Status and Trends data. We used discrete choice models to assess prey selection and visualized frequency of prey in diet and availability on the landscape over the fall migration season. Using eDNA metabarcoding, we detected prey species on 94.1% of the hawks swabbed (n=525/588) comprising 1396 prey species detections from 65 prey species. Prey frequency in diet and eBird relative abundance of prey species were correlated over the migration season for top selected prey species, suggesting prey availability is an important component of raptor-songbird interactions during fall. Prey size, flocking behavior, and non-breeding habitat association were prey traits that significantly influenced predator choice. We found differences between female and male hawk prey selection, suggesting that sexual size dimorphism has led to distinct foraging strategies on migration. This research integrated field data collected by a volunteer-powered raptor migration monitoring station and public-generated data from eBird to reveal elusive predator-prey dynamics occurring in an ephemeral raptor-songbird community during fall migration. Understanding dynamic raptor-songbird interactions along migration routes remains a relatively unexplored frontier in animal ecology and is necessary for conservation and management efforts of migratory and resident communities. ## Description of the data and file structure 1_Bourbour_2023_Metadata.csv Metadata associated with each environmental DNA (eDNA) sample. Header info: **sample_id** = unique sample identifier, **date** = date sample was taken, **species** = USGS bird code (SSHA=sharp shined hawk), **sex** = Male or female, **SSHA_weigh**= weight measured in grams, **prey** = prey item detected through eDNA denoted USGS bird code), **prey_name** = common name of prey item detected through eDNA, **prey_size** = prey species categorized into average mass (Tobias et al. 2022) to classify each species as small (<30 g), medium (between 30 and 60 g), or large (>60 g), **prey_mass =** average prey mass (extracted from Tobias et al. 2022)**, Migratory =** For migratory tendency, 200 we used Billerman et al. (2022) to classify species as resident or migratory (i.e., which included 201 both complete and partial migrants) in the Pacific Flyway. 2_Bourbour_2023_demultiplexed_reads_2015_2.zip Demultiplexed reads from generated from Illumina’s MiSeq PE300 (v3) platform from samples collected in 2015. Sample ID at the beginning of each file name. 3_Bourbour_2023_demultiplexed_reads_2016.zip Demultiplexed reads from generated from Illumina’s MiSeq PE300 (v3) platform from samples collected in 2016. Sample ID at the beginning of each file name. 4_Bourbour_2023_referencelibrary.csv Custom reference library of bird species (n = 205) that range in the Pacific Flyway according to species account range maps (Billerman et al. 2022). The R package PrimerMiner (Elbrecht & Leese 2017) to download all publicly available COI barcode sequences from NCBI and BOLD databases for each species and manually reformatted the data files to be compatible with the reference database format used by the R package DADA2 (Callahan et al. 2016). 5_Bourbour_2023_Prey_detections_2015.csv Prey detections obtained using the COI-fsdF and COI-fsdR (González‐Varo et al. 2014) from samples collected in 2015. Header info: Species = Prey items detected from eDNA samples excluding lure species, Total = total count per prey item across all beak eDNA Samples, Sample ID = Columns C-JR, Negative Controls = Columns JS-JT. 6_Bourbour_2023_Prey_detections_2016.csv Prey detections obtained using the COI-fsdF and COI-fsdR (González‐Varo et al. 2014) from samples collected in 2016. Header info: Species = Prey items detected from eDNA samples ex ## Sharing/Access information Repository for eBIRD data and analysis: Tim Mehan. 2023. [https://github.com/tmeeha/ggro\\_sharpie\\_prey.git](https://github.com/tmeeha/ggro\\_sharpie\\_prey.git)