design: we prepared DNA libraries using the integenX PrepX ILM 32i DNA Library Kit (Thermo Fisher Scientific, Waltham, MA, USA) run on the Apollo 324 System (Takara, Mountain View, CA, USA) with an insert size of 320 bp. We quantified library concentrations with Qubit v.3 to calculate the amount of DNA needed for PCR amplification of libraries. We then used the Apollo 324 System to clean PCR products with magnetic beads. We measured library quality and average read length with an Agilent 2200 TapeStation (Agilent, Santa Clara, CA, USA). We then performed qPCR on each sample using the KAPA Library Quantification Kit (Roche Sequencing and Life Science, Wilmington, MA, USA) and CFX96 Touch real-time PCR machine (Bio-Rad, Hercules, CA, USA). We diluted all samples to equimolar concentrations and multiplexed three pools of 20 samples each (including bird samples from a different, unrelated project).