Much of what is reported about the biology of the Cassin's Sparrow is poorly established and additional research on virtually any topic would be valuable. Perhaps the greatest need is to identify movement patterns and residency/reproductive tactics in areas where populations seem to fluctuate. Few individuals have been banded, and few studies of marked individuals have lasted more than two years. Radiotelemetry linked to satellite receivers may be needed to follow birds over long enough periods to fully understand seasonal movements, but technology for such studies is undeveloped. Existing satellite transmitters are too heavy for sparrow-sized birds, but this technology is evolving rapidly. Geolocators are not likely to be useful due to lack of site fidelity in many parts of range (birds outfitted with geolocators must be recaptured to download data from the device).
Reproductive status and success should be measured in a variety of places, then correlated with "reproductive index" information (140). The increase in studies of the effects of land management (grazing, controlled burning, and control of exotic plants) is encouraging and should be expanded, especially in northern parts of the range. Cassin's Sparrow use of land set aside in the Conservation Reserve Program (e.g., 109) is worth exploring more. Winter status and distribution could be better established with standardized surveys using broadcast of recorded song within winter range. Little is known about the status and biology of the Cassin's Sparrow in Mexico, and studies such as the recent report of wintering habitat use in Chihuahua (66) should be encouraged.