||A partially automated radio-tracking system with semi-continuous azimuth data collection and XYLOG5 and MAP computer programs for azimuth data analysis was used for studies of California quail (Callipepla californica) at the E.E. Wilson Wildlife Area, Oregon, in 1988 and 1989. Movements of 58 hens were monitored daily to determine nest locations and dates of incubation activities throughout 2 breeding seasons (May to mid-August). Locations for specified periods during the breeding season for nesting quail were used in 2 studies: 1) effect of methyl parathion application to home ranges; and 2) home ranges and habitats used. Foraging home ranges during the first one-half of incubation for 15 hens were treated with water (n = 8) or methyl parathion 4E (n = 7) at a rate of 0.56 kg a.i./ha. No significant measurable effects were found for rates of nesting success and recruitment to 15 days post-hatching between water and methyl parathion groups. A significantly lower hatching rate was found for the methyl parathion group wherein 71 of 103 (69%) eggs for control hens and 36 of 71 (51%) methyl parathion group hens hatched. No significant measurable effects were found for nest attentiveness from pre- to post-treatment period within groups and use of treated areas between groups. Home range sizes, nesting cover, and cover-type composition of home ranges were described for radio-tracked hens. During 4 periods of the breeding season, mean home range size ranged from 4 to 22 ha and was significantly smaller during incubation. Hens used roadsides, characterized by early seral stage vegetation, for nesting more frequently than expected in relation to availability, used cultivated fields less than expected, and did not use road surfaces, buildings, and foundations. Nest sites had significantly more bareground and less grass, shrub, and vertical cover than random sites and also were located in early successional vegetation. Ability to collect azimuth data and precisely analyze locations and home ranges for hens within a 6-hour period daily throughout the 2 field seasons were advantages of the radio-tracking system. Small sample size largely because of transmitter failures, potential for system overload, expenses incurred to employ personnel, and subjectiveness of collected azimuth data were disadvantages of the system. Efforts to advance radio-tracking technology should focus upon development of remote antennas, which are computer-controlled to collect and relay azimuth data to a central station.