Status of Cassin's Sparrow in Arizona

Abstract

As long ago as May, 1940, the writer became aware that current ideas concerning the status of the Cassin's Sparrow (Aimophila cassini) in the western part of its range were in need of revision. For three years, however, publication of these findings was withheld while further data were in prospect. Since it now appears unlikely that additional light will be thrown on the problem in the near future, I wish to call attention at this time to a situation which appears to be unique among North American birds. This sparrow first attracted the author's attention on July 19, 1939. On that date, with his friends Gale Monson and F. W. Loetscher, Jr., he visited a locality near Tucson, Arizona, where he had previously discovered surviving colonies of Rufous-winged Sparrows (Aimophila carpalis). He hoped to find a nest of the latter species while introducing it to his friends, who had never seen a Rufous-winged Sparrow before July, 1939. While driving along the road and visiting the Rufous-winged Sparrow colonies, the party saw about twenty-five Cassin's Sparrows, most of them males singing the hauntingly sweet song of this otherwise obscure sparrow. Under other circumstances, no particular attention might have been paid to them; ever since the days of Henshaw, in the early 1870's, it has been well known that the Cassin's Sparrow is often abundant in the grasslands of southeastern Arizona in late summer. Indeed, Loetscher and I had seen and taken these sparrows the day before at Sahuarita (south of Tucson) and on the Santa Rita Range Reserve without suspecting that anything was amiss. But on July 19 it was clear to me that there was something peculiar about these birds. Here they were in numbers, singing freely, and the males evidently in breeding condition, with their testes greatly enlarged; yet hardly a month before, and with no period intervening when our sparrows were supposed to be migrating, on June 16, 1939, I had visited these self-same spots without hearing or seeing a single Cassin's Sparrow! My next opportunity to visit these localities came in late August, a month later. The Cassin's Sparrows were still common on August 21 and 22; there were still quite a number of them, giving their flight song, on August 24 and 28; there were a few on September 1 and 6, but in September I heard little singing. By mid-September, what little singing there was was reduced to mere fragments of the full song. My last visit at this period was on September 12, when Lee W. Arnold and I saw only two Cassin's Sparrows.