Hazards of soil Pb to wild birds may be more accurately quantified if the bioavailability of that Pb is known. To better understand the bioavailability of Pb to birds, we measured blood Pb concentrations in Japanese quail (Coturnix japonica) fed diets containing Pb-contaminated soils. The in vitro bioaccessibility of Pb (IVBA Pb) in the test soils was then measured in seven in vitro tests and regressed on relative Pb bioavailability (RBA Pb) to produce predictive in vivo in vitro correlation (IVIVC) equations. The bioaccessibility methods were: U.S. EPA Method 1340 at pH 1.5, the same test conducted at pH 2.5, the “Ohio State University In vitro Gastrointestinal” method (OSU IVG), the “Urban Soil Bioaccessible Lead Test”(USBLT), the modified “Physiologically Based Extraction Test” (PBET) method, the “Waterfowl Physiologically Based Extraction Test” (W-PBET) and the Avian Ohio State University (AOSU) method. Further studies with diet included in the in vitro methods were performed for the U.S. EPA 1340 pH 1.5 method, the modified U.S. EPA 1340 pH 2.5, and the AOSU. Based on criteria of slope and coefficient of determination, the modified U.S. EPA Method 1340 pH 2.5 and OSU IVG tests performed very well for fasted (i.e., no diet addition) conditions. The AOSU was able to accurately predict RBA Pb (RBA Pb = 1.94 IVBA Pb -12.0, r² = 0.92). Results suggest that an IVIVC derived from either a diet+soil or soil-alone method would yield a predictive equation to estimate RBA Pb.