Seasonality of the Arctic WarblerPhylloscopus borealisin Northern Korea, with Refutation of Previous Assumptions of Korean Breeding

Abstract

Standard reviews list Arctic Warbler Phylloscopus borealis as a probable breeder in northern Korea, as well as passage migrant; the most recent states that spring passage begins c. 10 April and finishes within May. Near-daily structured counts in north-central Korea (Pyongyang and Hyangsan) during 2000–2003 showed, by contrast, that regular spring passage runs from early-mid May into early June, and that autumn return begins in early August, dates reflecting modern data from elsewhere in East Asia. Specific searches in the Myohyang Mountains, site of most postulated ‘breeding’ records, found no evidence of summer residency, let alone breeding. Korean breeding was assumed from records outside the then-perceived passage seasons, but these perceptions were flawed and, combined with misidentification, led to the unsupportable conclusions of breeding. In fact, a summer gap in acceptable past records spans almost the same dates as today's summer absence from Pyongyang and Hyangsan, both undoubtedly only passage sites. The species may yet be found to breed in northern Korea, but there is no evidence, even circumstantial, that it does so. Past assessments that regular passage begins in mid April were evidently in error, reflecting past difficulties of species identification.