THE PROBABLE BREEDING OF CASSIN’S SPARROW (Peucaea cassinii) IN PINAL COUNTY
Doug Jenness, 4375 E. Rollins Rd., Tucson, AZ 85739
Most breeding bird surveys in Arizona are conducted in the late spring and early summer when most birds that breed in the state are expected to be nesting. However, this opens the possibility of missing species that typically breed in response to the onset of monsoon rains in July. One of these overlooked species is the Cassin’s Sparrow (Peucaea cassinii; Fig. 1). This may have been the case in Pinal County, where there was no recent evidence of even possible nesting for Cassin’s Sparrow before 2000 (Corman 2005). Following an especially wet monsoon season in 2006, Cassin’s Sparrows were discovered singing and skylarking in an extensive semidesert grassland area from Oro Valley in northern Pima County to east of Oracle in Pinal County (Fig. 2). The skylarking behavior of singing males in July and August suggested the presence of females and probable nesting (Dunning et al. 1999)1. Surveys by the author that summer documented an extensive area where breeding behavior was detected (Jenness 2008).
Phillips et al. (1964) include a map that includes sites of wintering Cassin’s Sparrow in the Willow Springs Road-Oracle area, but there are no documented reports during breeding season. The surveys during the Arizona Breeding Bird Atlas between 1993 and 2000 in that area didn’t detect any Cassin’s Sparrows, but these surveys were conducted in April and
May before typical singing and other breeding behavior for this sparrow begins (Troy Corman, correspondence to the author, 12 July 2012). There have never been established North American Breeding Bird Survey routes in that area but even if there had been, these surveys would have been conducted before the summer monsoon period. As Corman (2005) indicates “Many potential breeding records for this wandering, rain-dependent sparrow were likely missed due to lack of sufficient surveys in shrubby grasslands and Chihuahuan desertscrub associations in late July and August.”
The presence of Cassin’s Sparrow in this area posed several questions: Was the 2006 discovery a one-year phenomenon due to unusually high rainfall that summer, or more likely, is there a breeding population that may have been previously undetected? If there is an annual breeding population is it usually confined to a smaller area that expanded in 2006 due to unusually high rainfall?
The greatest dispersion in the five-year period was in the summer of 2011. This coincided with an unusual invasion of singing Cassin’s Sparrows into other parts of the state, most notably into northern counties, including first records for Mohave and Navajo counties. Four additional areas along Hwy. 77 between Oracle Junction and Oracle were surveyed in 2011. In this banner year for Cassin’s Sparrow these sites proved very productive. For example, along a 2.3-km section of Rockcliff Rd. going north from Highway 77 in Oracle, 10 singing sparrows were detected on one survey (Table 1). Only singing and skylarking males were detected during the five-year period and no nests or tangible signs of nesting were observed. Even though no nests have yet been discovered, extensive breeding behavior in this appropriate habitat suggests that nesting is likely taking place annually and this may well have been the case for many years prior to 2006.
The habitat in the survey area includes many different species of grass (Jenness 2008), but except for one small tract is extensively grazed by livestock. The abundance of grass varies considerably depending on rainfall. Only rarely, as in 2006, could grass vegetation be described as lush; usually it is sparse. The exception is a 162-hectare tract of combined state trust land and private land, 3.2 km south of the center of Oracle, that hasn’t been grazed for at least 10 years. It has a large variety and abundance of grasses, especially Arizona Cottontop (Digitaria californica). This area was visited in the summers of 2010 and 2011, and at least one singing Cassin’s Sparrow was detected in the latter year. Interestingly, Botteri’s Sparrows (Peucaea botterii) were reported from this area in August 2010 by Bruce Taubert and Bud Bristow and confirmed (via photo) by the author the following month. They were also reported in 2011 and 2012. The reports from this area are the only documented sightings in Pinal Co. since the 1940s (Phillips et al. 1964).
The two-month rainfall for July and August in three of the study years (2007, 2010, and 2011) ranged from 10.6 to 14.1 cm, which was considerably lower than the 2006 level of 29.1 cm. The figures for 2008 and 2009 were not available (NOAA, 2006-11). It is difficult to determine if any of the Pinal County Cassin’s Sparrows are resident year-round as they are usually silent and elusive when not breeding. However in the spring of 2009, following winter rainfall a bit above normal for recent drought years, a male Cassin’s Sparrow was heard singing along Willow Springs Rd. as early as 1 March and again on 15 March and 9 May. This suggests that some birds may occasionally overwinter.
There are not enough data to determine whether the population in the study area is declining or expanding. The tendency for Cassin’s Sparrow in Arizona to surge in especially wet summer seasons adds to the difficulty of detecting changes in long-term population fluctuations. The study area appears to be an outlier that is not contiguous with the principal breeding region in the southeastern part of the state, where Cassin’s Sparrows have been noted as fairly common and widespread (Corman 2005). Although they had earlier been reported north to the San Carlos tribal lands and beyond Globe (Monson and Phillips 1981) the breeding bird surveys for the Atlas period didn’t detect any there. They have, however, been reported irregularly and locally from several locations in Yavapai County since the 1970s.
Special thanks to Troy Corman, Mark Stevenson, and Carl Tomoff for making many helpful suggestions on the content and organization of the article.
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Accepted 15 January 2013