This dataset includes captures of mainly Grasshopper Sparrows (GRSP), but includes other songbirds. Each row pertains to an individual captured on a certain day. Individuals can repeat. Most captures include data on age, sex, head-bill, tarsus, wind chord, molt score, fat score, and mass. In many cases, a single feather was collected from each Grasshopper Sparrow for isotopic analyses, and when available, results of those data are included. Some individuals were measured for body composition (fat mass, lean mass, and body water) using a mobile Quantitative Magnetic Resonance (QMR) machine.