Revealing undocumented or poorly known flight calls of warblers (Parulidae) using a novel methodof recording birds in captivity

Abstract

Flight calls are commonly produced by nocturnal migrant birds. Uncertain or unknown identities and lack of information about inter- and intraspecific variation in call notes limit the usefulness of flight calls in monitoring bird populations. We developed a novel method for recording flight calls of temporarily captive birds that allows us to study inter- and intraspecific variation in call notes of birds of known identity, age, and sex. We recorded calls and analyzed data from 13, 271 flight calls recorded from 469 individuals of 28 warbler species (Parulidae) over a two-year period. Principal coordinate ordination of spectral cross-correlation data on 7 of the 28 species indicated that flight calls recorded in captivity are similar to those recorded from wild birds. Visual and aural comparisons of species' flight calls from these two different types of recordings support these results. Additionally, we verified flight calls previously identified primarily on inferential evidence and report on previously undocumented flight calls. This method quickly provides many high-quality recordings of the flight calls of individuals of known age and sex, and the results of our analyses greatly facilitate the development of automated sound-analysis algorithms critical for implementing and strengthening future acoustic monitoring applications. © The American Ornithologists' Union, 2009.