in press

Several recent studies indicate that the consistency of song or syllable repetitions signals male quality. However, the comparability and efficacy of different measurement methods is not known. Here, I compared two approaches to measuring the consistency of syllable repetitions within the trills of House Wren (Troglodytes aedon) songs. In the first approach, I calculated the coefficient of variation (CV) in standard time–frequency measurements within each trill. In the second approach, I used spectrogram cross-correlation (SPCC), which measures the maximum pixel-by-pixel similarity of two spectrograms. The two approaches gave correlated estimates of trill consistency, but SPCC was more strongly related to two putatively biologically relevant traits: specifically, SPCC differed more strongly between age classes, and more variation in SPCC could be attributed to individual differences. CV-based measures complemented SPCC measures by clarifying some of the specific acoustic features whose consistency changed with age. Although additional comparisons between measurement approaches would be useful to assess generality, it appears that researchers interested in song or trill consistency should consider using an SPCC, or a combined SPCC- and CV-based, approach.

The vocal repertoire of the Asiatic Black Bear (Ursus thibetanus) has been poorly studied and until recently only two call types (chuffing and humming) have been described. Here I investigate the vocalizations of three wild orphaned cubs (two males and one female) reared by two observers in natural conditions in the Russian Far East. I grouped the calls into structural types, and then compared them with existing literature data on vocalizations of the same, as well as other species of the Ursidae family. In total, 1302 calls were classified visually from spectrograms into seven call types: whine, moan, yelp, grunt, snort, chuffing and humming. Classification results were verified with discriminant function analysis and randomization. I also fixed the presence of nonlinear phenomena (NLP) and articulation effects in calls. Whine was the most frequently recorded, as well as the most structurally variable call type due to a high rate of NLP. These results indicate that the vocal repertoire of the Asiatic Black Bear cubs is graded, but includes at least two discrete sound types. This work needs to be continued with further studies of vocalizations of cubs and adults of this species to verify the results of this preliminary study.

In several avian and mammal social species, contact calls are hypothesized to function in maintaining group cohesion, coordinating activities between group members and negotiating fissions and fusions of multiple groups during foraging and roosting. They are therefore expected to exhibit acoustic features that make them suitable for communication of identity information. We investigated this in the monomorphic Peach-fronted Conure, a tropical parakeet living in open forest and scrubland habitats. The species is highly social outside the breeding season where it is assumed to live in a fission–fusion social system. In this study, contact calls from 10 visually isolated male and female Peach-fronted Conures were recorded outside the breeding season. Results from the multivariate analysis of variance and spectrographic cross-correlation with principal coordinates analysis procedure showed that contact calls varied highly between individuals and indicated that caller identity could be encoded in the duration, peak frequency, max frequency and 25%, 50% and 75% frequency energy quartiles of contact calls. The 50% frequency and 75% energy quartile was also significantly higher for females than for males. Furthermore, the results showed an inverse relationship between two morphometric measures and two spectral parameters, suggesting that variation in call parameters could also allow receivers to obtain information about the body size of the caller. Discriminant function analysis showed that contact calls could be correctly classified to individuals in 100% and to sexes in 91% of the cases, suggesting that there is sufficient variation in contact call parameters to enable vocal recognition of individuals and sex.

Understanding the sources and magnitudes of variation in signal traits is an important first step towards understanding the forces that may act on signal evolution. In anuran amphibians, acoustic communication plays a major role in the processes of mate attraction and aggression. The significance of variation in characteristics of the mate-attracting advertisement calls is relatively well understood, whereas another call type, the aggressive call, has received much less attention. I recorded both advertisement and aggressive calls given by male grey treefrogs, Hyla versicolor, in staged competitive interactions. From these recordings, I assessed the effects of physical and abiotic influences on signal production by measuring the correlations between the call characteristics of both call types and variables associated with size, body condition and body temperature. I also estimated within- and between-male variation in call characteristics. Temperature affected diverse characteristics of both call types, whereas the effects of morphology were limited primarily to call-frequency variables. Spectral characteristics of both call types were largely static within males, whereas gross-temporal characteristics were much more variable. Within each call type, many of the call characteristics were correlated with one another, whereas between call types, there were relatively few strong correlations between call characteristics. I discuss these results in terms of their implications for signal evolution, mate choice and assessment in contests.

The Red-billed Leiothrix (Leiothrix lutea) is an invasive species which has recently been found to be locally abundant in eastern Liguria (Italy). The song production of this bird was recorded over the course of an entire year (2011) and evaluated using both aural information and applying innovative automatic processing metrics. Our findings revealed that the Red-billed Leiothrix has loud vocalizations that are heard for most of the year, including in July and August when other birds are silent. Its song production has been estimated to amount to 37% of the sounds uttered by the entire bird community. The next most vocal species are the European Robin (36%), the Common Blackbird (18%), the Subalpine Warbler (5%) and the Sardinian Warbler (1%). The Red-billed Leiothrix can be seen as a new acoustically dominant species and, consequently, a potential modifier of the soundscape patterns of the indigenous bird community. The modification of acoustic traits in the repertoire of both indigenous species and the Red-billed Leiothrix is to be expected according to a co-evolution hypothesis.