Soft Song in Song Sparrows: Acoustic Structure and Implications for Signal Function

In many species of songbirds, males sometimes produce songs at distinctly lower amplitude than in normal singing. Depending on the species, these 'soft songs' may be sung in the context of female courtship, male–male aggression, or both. In song sparrows, males produce soft songs during aggressive interactions with other males, and the amount of soft song produced is the only singing behavior that can be used to reliably predict a subsequent attack by the singer. Although soft song is clearly an important signal in this species, little is known about the acoustic structure of soft song or about how that structure compares to the structure of normal 'broadcast song'. We recorded a large sample of soft songs and broadcast songs from 10 male song sparrows, and measured song amplitudes in the field while controlling the subject's distance to a calibrated microphone. We show that song sparrow males produce songs over a wide range of amplitudes, with soft songs in the range of 55–77 dB sound pressure level and broadcast songs in the range of 78–85 dB. We present evidence for two types of soft song: 'crystallized' soft songs that are broadcast repertoire song types sung at low amplitude, and 'warbled' soft songs that are not found in the broadcast repertoire. Although highly variable, warbled soft songs produced by individual birds could be grouped into song types based on spectrographic similarity. To our knowledge, a distinct repertoire of soft song types has not been previously reported for any songbird.     

Anthropogenic Metal Content and Natural Background of Overbank Sediments from the Mining District of Guanajuato,Mexico

In many mining districts, metal pollutants from mine tailings have historically been dumped into local streams. The purpose of this study was to determine the concentrations of Pb, Cu, Zn, Mo, Sb, Cs, Cr, Sc, Co, Ni, and Li in eight overbank-sediment profiles from the Guanajuato River, in the Guanajuato mining district and to establish geochemical background values using direct and indirect methods. The background levels calculated using the direct method in pristine overbank deposits were similar to or slightly higher than the upper crustal values for Sc, Cr, Co, Ni, Zn, and Mo (17.3, 108.7, 18.7, 44.4, 97.2, and 1.1 mg/kg, respectively). In contrast, levels of Cu, Cs, and Pb were up to two times higher than crustal values (93.1, 11.2, and 37.5 mg/kg, respectively), and the median concentration of Sb was 8.2 mg/kg, up to 20 times the crustal level. These natural anomalies can be explained by the presence of mineral deposits in the Guanajuato mining district. Ni and Cr were provided by the ultramafic rocks of the Sierra de Guanajuato. The geochemical backgrounds established with the indirect method of Sc, Cr, Co, Ni, and Mo were lower than those found in the natural background. Moreover, the geochemical backgrounds established with the indirect method of Cu, Zn, Sb, Cs, and Pb were higher than those found in the geochemical background established with the direct method. Contamination levels calculated by the geoaccumulation index (Igeo) indicated moderate to strong contamination for Cu, Zn, Sb, and Pb in more than half of the samples. This contamination may be attributable to historical discharges of mine tailings in the Guanajuato River and the use of Cu during the metallurgical process of amalgamation. Our results provide evidence that anthropogenic metals stored in the fluvial plain of the Guanajuato River represent a major potential source of pollutants to surface and groundwaters downstream from the study area in the Lerma-Santiago basin.