368,381 research outputs found
Song post exposure, song features, and predation risk
No full textMale birds use song to attract mates and deter other males, but in doing so, they also attract the attention of predators and parasites. Such viability costs are inherent in reliable signals, potentially causing females to prefer mates that display from the most exposed sites. However, viability costs of sexual signals may be ameliorated by affecting the choice of microhabitat, which in turn may affect the design of song features that are most efficiently transmitted in this microhabitat. We estimated the exposure of song posts (microsites used by males when singing) used by passerine birds in relation to prey selection by the sparrowhawk Accipiter nisus, by calculating the proportion of males that sang from song posts that were at the maximum level of the vegetation, in an attempt to quantify the costs of sexual selection. We quantified prey susceptibility to predation as the difference between the log-transformed observed number of prey minus the log-transformed expected number of prey in the environment. This prey susceptibility index increased with increasing song post exposure similarly in sexually dichromatic and monochromatic species, although the prey susceptibility index was related to sexual dichromatism. Song post exposure was dependent on habitat, but comparative models controlling for the potentially confounding effects of habitat, sexual dichromatism, hole nesting, coloniality, body mass, cognitive capacities, and flying abilities indicated that the relationship between the prey susceptibility index and song post exposure is strong. Path analyses of the relationship between song post exposure, sexual dichromatism, and prey susceptibility index revealed that selection acting on sexual dichromatism and song post exposure has secondary impact on prey susceptibility index. The opposite causal mechanisms by which predation affects sexual traits are less likely. These models suggest that female preference for high song posts or dichromatic plumage increases predation risk on an evolutionary time scale. Copyright 2006.birds; costs of sexual selection; prey selection; sound transmission
The evolution of song in female birds in Europe
No full textBird song is usually regarded as an attribute of males. However, in some species, females may also produce songs even with comparable complexity to that of males. It has been suggested that female song may evolve due to similar selection pressures acting on males, but no study has yet investigated the evolution of female vocalization in a phylogenetic context, a gap that we intended to fill with this study. Based on standard descriptions in The Birds of Western Palearctic, we classified 233 European passerine species with respect to whether females are known to produce songs or not. We were more likely to find information on female song for species whose song is more studied than for less intensively studied species. When we traced information on female song on a phylogeny, we found that at least in 2 avian families, female song appeared to be the ancestral state, but such an ancestral state may be expected to be even deeper in the phylogenetic tree with increasing information on female song. In fact, we cannot exclude the possibility that the ancestor of European passerines had females capable of singing. In a preliminary comparative study based on the available data, we found some evidence that female song may have evolved under the influence of sexual selection as carotenoid-based dichromatism was positively related to female song among species. Our findings imply that due to publication bias, the evolutionary importance of female song is generally underestimated. Copyright 2007.bird song; calls; comparative study; female vocalization; repertoire size; sexual selection
Sexually size dimorphic brains and song complexity in passerine birds
No full textNeural correlates of bird song involve the volume of particular song nuclei in the brain that govern song development, production, and perception. Intra- and interspecific variation in the volume of these song nuclei are associated with overall brain size, suggesting that the integration of complex songs into the brain requires general neural augmentation. In a comparative study of passerine birds based on generalized least square models, we tested this hypothesis by exploring the interspecific relationship between overall brain size and repertoire size. We found no significant association between song complexity of males and brain size adjusted for body size. However, species in which males produced complex songs tended to have sex differences in overall brain size. This pattern became stronger when we controlled statistically for female song complexity by using sex differences in song complexity. In species with large differences in song complexity, females evolved smaller brains than did males. Our results suggest no role for the evolution of extended neural space, as reflected by total brain size, owing to song complexity. However, factors associated with sexual selection mirrored by sex differences in song complexity were related to sexual dimorphism in overall brain size
Age-dependent health status and song characteristics in the barn swallow
No full textBird song has been hypothesized to evolve, partly, to signal health status of males, and song features should therefore correlate with parasite load. Immune function, parasitism, and secondary sexual characters can, however, differ between age classes, and any apparent relationship between song and parasite loads can be the result of systematic age effects. We tested for an age-dependent relationship between sexually selected characters and measures of parasitism in a Spanish population of the barn swallow Hirundo rustica. A comparison across age classes revealed that chewing lice load, song duration, mean peak amplitude frequency of songs, and tail length differed significantly between yearlings and adults. In a longitudinal analysis, we found significant evidence for mean peak amplitude frequency of songs, tail length and chewing louse parasitism, and a nonsignificant tendency for song duration to change with age of an individual. We found a significant association between song duration and chewing louse load and between hematocrit and peak amplitude frequency of the rattle, the typical harsh terminal syllable. In tests for associations between song traits and health status, while controlling for age, age and chewing louse load were independently related to song duration. We found a significant relationship between pairing success and song duration, implying that females may use this song trait in their choice of parasite-free males. Although the song of the barn swallow may provide information about both male age and parasite resistance, signaling of health status appears to be independent of age effects, in accordance with the theory of parasite-mediated sexual selection, suggesting that male signals can be used as reliable indicators of parasitism. Copyright 2005.age; barn swallow; bird song; chewing louse; hematocrit; sedimentation rate
Song sharing and repertoire change as indicators of social structure in the Noisy Scrub-bird
No full textThe Endangered Noisy Scrub-bird is a small passerine that is seldom seen but often heard in its range on the south coast of Western Australia. The difficulties in observing this cryptic bird mean that little is known about its social system. The loud, conspicuous territorial song of the male provides a convenient, non-intrusive means by which to study this species.
The aim of this project was to investigate the patterns of song sharing and repertoire change in the Noisy Scrub-bird to provide indications of the social structure. It was found that groups of up to ten territorial males shared the same set of about five song types. Song groups were discrete, with members of a song group sharing most, if not all, of their song types. Males from different song groups had no song types in common.
Repertoire change was rapid and, with the exception of one individual, was found in every territorial male studied in the Mt Gardner population. It occurred simultaneously in all members of a song group, with males making the same changes to their shared songs. The source of repertoire change was mainly modification of existing song types with occasional divergence of a single song type into two distinct song types, as well as some innovation providing new song types. The average life of a song type was approximately 6 months. Although some song types persisted for the entire 16 month sampling period, they were continually modified and a year later could no longer be recognised as the same type.
Translocation of eight male scrub-birds to the Porongurup National Park provided an opportunity to combine individuals that initially did not share any songs. This allowed the process of song group formation to be studied. Within a one to two month period these males altered their songs so that they shared with their new neighbours. There was some evidence that the songs of dominant males were copied. Observation of the population established on Bald Island by translocation confirmed that there were no appreciable long-term effects on the songs of translocated Noisy Scrub-birds. Song group size, repertoire size and levels of song sharing were very similar to those found in the Mt Gardner population.
The striking feature of Noisy Scrub-bird song groupings was their discreteness and cohesiveness even in the presence of continual repertoire change. It is suggested that each song group consists of a dominant male whose songs are more attractive to females and/or effective in territory defence. This dominant male is surrounded by subordinate males that copy his effective songs. Repertoire change can be explained by the dominant male continually making changes to his songs, with the other males copying these changes to retain their mimicked effectiveness. Each song group may in fact represent a dispersed lek. The scenario suggested to explain Noisy Scrub-bird song groupings bears striking similarities to the hotshot hypothesis to explain lek formation whereby males cluster around a successful male.
This study demonstrates the potential of using song to investigate aspects of the social system of a species which is otherwise very difficult to observe. Management of an Endangered species such as the Noisy Scrub-bird will always benefit from increased knowledge about their social system. For example, this study showed that taking males from different song groups for translocation probably has little impact on their success at the new site because of their ability to rapidly alter their songs to form new song groups. An additional benefit of regularly monitoring the songs of translocated males was that it allowed ongoing identification of individuals, even though their songs were continually changing
Understanding sedimentation in the Song Hong–Yinggehai Basin, South China Sea
No full textThe Cenozoic Song Hong–Yinggehai Basin in the South China Sea contains a large volume of sediment that has been used in previous studies, together with regional geomorphology, to argue for the existence of a large palaeodrainage system that connected eastern Tibet with the South China Sea. To test this and to understand the significance of sediment volumes deposited in the Song Hong–Yinggehai Basin, this study compared erosion histories of source regions with sediment volumes deposited during the two main stages in basin evolution spanning active rifting and subsidence (30–15.5 Ma) and postrift sedimentation (15.5 Ma to present). The study of basin provenance by detrital zircon U-Pb dating revealed Hainan was an important and continuous source of sediment, and a bedrock thermochronological study quantified its overall contribution to basin sedimentation. Comparison between the accumulated mass of basin sediment and volumes of eroded bedrock, calculated from apatite thermochronometry across the modern Red River drainage in northern Vietnam as well as Hainan Island, accounted for the bulk of sediment deposited since 30 Ma. Consequently, if an expanded paleodrainage ever existed it must have predated the Oligocene
Extrapair paternity and the evolution of bird song
No full textBird song is usually considered to have evolved in the context of sexual selection. Because extrapair paternity is a major component of sexual selection, mating advantages at the social level for males that produce songs of high quality may be transformed into higher success in extrapair paternity. Therefore, males with longer and more complex songs should suffer less from extrapair paternity intraspecifically, whereas species with high rates of extrapair paternity, reflecting intense sperm competition, should produce more elaborate songs. Although some intraspecific studies demonstrated a negative link between features of songs and extrapair paternity in own nest, others failed to detect such a relationship. Contrary to expectation, a meta-analysis of all studies revealed no significant intraspecific evidence for songs being associated with extrapair paternity. In addition, in comparative analyses based on generalized least squares (GLS) models, we found that no measures of song complexity and temporal output were significantly related to extrapair paternity interspecifically, even when potentially confounding factors such as social mating system, life history, migration, habitat, or sexual dichromatism were held constant. Only plumage dichromatism was significantly related to extrapair paternity. The absence of both intra- and interspecific relationships between measures of song variability and extrapair paternity suggests that factors other than postmating sexual selection have been the important evolutionary forces shaping differences in song. Copyright 2004.bird song; evolution; extrapair paternity; generalized least squares; meta-analysis; repertoire size; sexual selection
Seasonal changes in patterns of gene expression in avian song control brain regions
No full textPhotoperiod and hormonal cues drive dramatic seasonal changes in structure and function of the avian song control system. Little is known, however, about the patterns of gene expression associated with seasonal changes. Here we address this issue by altering the hormonal and photoperiodic conditions in seasonally-breeding Gambel's white-crowned sparrows and extracting RNA from the telencephalic song control nuclei HVC and RA across multiple time points that capture different stages of growth and regression. We chose HVC and RA because while both nuclei change in volume across seasons, the cellular mechanisms underlying these changes differ. We thus hypothesized that different genes would be expressed between HVC and RA. We tested this by using the extracted RNA to perform a cDNA microarray hybridization developed by the SoNG initiative. We then validated these results using qRT-PCR. We found that 363 genes varied by more than 1.5 fold (>log(2) 0.585) in expression in HVC and/or RA. Supporting our hypothesis, only 59 of these 363 genes were found to vary in both nuclei, while 132 gene expression changes were HVC specific and 172 were RA specific. We then assigned many of these genes to functional categories relevant to the different mechanisms underlying seasonal change in HVC and RA, including neurogenesis, apoptosis, cell growth, dendrite arborization and axonal growth, angiogenesis, endocrinology, growth factors, and electrophysiology. This revealed categorical differences in the kinds of genes regulated in HVC and RA. These results show that different molecular programs underlie seasonal changes in HVC and RA, and that gene expression is time specific across different reproductive conditions. Our results provide insights into the complex molecular pathways that underlie adult neural plasticity
Comparison of Eurovision Song Contest Simulation with Actual Results Reveals Shifting Patterns of Collusive Voting Alliances.
No full textThe voting patterns in the Eurovision Song Contest have attracted attention from various researchers, spawning a small cross-disciplinary field of what might be called 'eurovisiopsephology' incorporating insights from politics, sociology and computer science. Although the outcome of the contest is decided using a simple electoral system, its single parameter - the number of countries casting a vote - varies from year to year. Analytical identification of statistically significant trends in voting patterns over a period of several years is therefore mathematically complex. Simulation provides a method for reconstructing the contest's history using Monte Carlo methods. Comparison of simulated histories with the actual history of the contest allows the identification of statistically significant changes in patterns of voting behaviour, without requiring a full mathematical solution. In particular, the period since the mid-90s has seen the emergence of large geographical voting blocs from previously small voting partnerships, which initially appeared in the early 90s. On at least two occasions, the outcome of the contest has been crucially affected by voting blocs. The structure of these blocs implies that a handful of centrally placed countries have a higher probability of being future winners.Simulation, Perl, Eurovision Song Contest, Voting Blocs, Collusive Voting
Sexual selection on song and cuticular hydrocarbons in two distinct populations of Drosophila montana
No full textSexual selection has the potential to contribute to population divergence and speciation. Most studies of sexual selection in Drosophila have concentrated on a single signaling modality, usually either courtship song or cuticular hydrocarbons (CHCs), which can act as contact pheromones. We have examined the relationship between both signal types and reproductive success using F1–3 offspring of wild- collected flies, raised in the lab. We used two populations of the Holarctic species Drosophila montana that represent different phylogeographic clades that have been separate for ca. 0.5 million years (MY), and differ to some extent in both traits. Here, we characterize the nature and identify the targets of sexual selection on song, CHCs, and both traits combined within the populations. Three measures of courtship outcome were used as fitness proxies. They were the probability of mating, mating latency, and the production of rejection song by females, and showed patterns of association with different traits that included both linear and quadratic selection. Courtship song predicted courtship outcome better than CHCs and the signal modalities acted in an additive rather than synergistic manner. Selection was generally consistent in direction and strength between the two populations and favored males that sang more vigorously. Sexual selection differed in the extent, strength, and nature on some of the traits between populations. However, the differences in the directionality of selection detected were not a good predictor of population differences. In addition, a character previously shown to be important for species recognition, interpulse interval, was found to be under sexual selection. Our results highlight the complexity of understanding the relationship between within-population sexual selection and population differences. Sexual selection alone cannot predict differences between populations.Peer reviewe
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