Bird capture, husbandry and tissue collection:
We captured adult house sparrows using mist nets from sunrise until measured wing chord (to the nearest 1 mm), tarsus length (to the nearest 1 mm), and body mass (to the nearest 0.1 g). We also collected approximately 50 µl of blood from the brachial vein of each bird, which was stored in 300 µl of DNA/RNA Shield (Zymo R1100-50). Immediately after, each bird was injected subcutaneously with 100 µl of 1 mg ml⁻¹ LPS (from E. coli 055; Fisher L4005) in sterile saline over the breast muscle. Birds were housed individually in wire songbird cages (approx. 35.6 x 40.6 x 44.5 cm) with food and water provided ad libitum , while maintaining visual and vocal contact. Forty-eight hours post-injection, between 0700 and 1000, birds were euthanized via isoflurane overdose followed by rapid decapitation. We then collected liver, spleen, and gut samples in 500 µl of DNA/RNA Shield, and all samples were stored at -80°C until further analysis. We chose these tissues because the goal of the larger project for which we collected sparrows involves epigenetic regulation of immune gene expression; these tissues are among the most active lymphoid tissues in the body. All animal procedures complied with local ethical guidelines, approved by the USF IACUC (IS00011653) and relevant authorities in the countries of capture. Export and import of animal tissues followed all relevant U.S. regulations, including USDA-APHIS permits.