Passerina ciris occurs in two geographically disjunct populations: a western population breeding from northern Mexico to northern Texas, USA, and wintering in south-west Mexico; and an eastern population breeding along the Atlantic coast from North Carolina to Florida (USA) and wintering in southern Florida and the Caribbean (Lowther et al. 1999). The global population is estimated to be 3.6 million birds (Rich et al. 2003). Populations have declined since the mid-1960s and the species has been extirpated from parts of its range in south-west and east USA and north-east Mexico (Lowther et al. 1999, Sauer et al. 2003, NAS 2004, USFWS 2004). Breeding Bird Survey data from the continental USA (and for five years from north-east Mexico) indicates that the population has declined by 55% over the last 30 years (IÃ±igo-Elias et al. 2002, Rich et al. 2003), with the steepest declines in the eastern population.