Black-throated Sparrow is an attractive and boldly-marked sparrow of dry western deserts from Texas to California and from Mexico to southern Oregon and Idaho. Its seasonal movements are not strongly pronounced, but it does withdraw from its more northerly breeding areas in winter.
The short-distance movements of some of the dry-country species in the American West are not particularly well-known. Their habitats tend to be poorly covered and studies on the species focus on breeding and winter periods. eBird data–and particularly models like this that compensate for effort and other variables–hold promise in learning more about where, when, and how species like Black-throated Sparrow migrate. Being adapted to desert climates, their requirements for molt and migration are certainly quite different from riparian and montane species in the West, several of which have molt and migration strategies that cause them to move widely within the West in search of areas that regularly get late summer rains.
In the Black-throated Sparrow animation above the northward push appears to happen quite early, but we would be interested to hear from local birders if Black-throated Sparrows really reach their more northerly breeding areas in March. In Colorado, the species does not occur regularly in winter and its return is in April, so it does seem like this model may b struggling with the precise arrival dates and the extent of winter occurrence.
The southward movements seem to happen mostly in October, but like many sparrows, there may be some “facultative migration” in response to winter weather conditions. This is generally believed to be a factor in White-throated Sparrows and other species in the East which may try to overwinter in the north, but can move farther south if especially cold weather strikes.