The Probable Breeding of Cassin's Sparrow in Pinal County
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). 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. 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). 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?