@article {53364, title = {Quiet violence: Savannah Sparrows respond to playback-simulated rivals using low-amplitude songs as aggressive signals}, journal = {Ethology}, volume = {124}, year = {2018}, month = {Jan-10-2018}, pages = {724 - 732}, abstract = {

When animals compete over resources such as breeding territories, they often use signals to communicate their aggressive intentions. By studying which signals are associated with aggressive interactions, we gain a deeper appreciation of animal behaviour. We studied aggressive signalling in male Savannah Sparrows, Passerculus sandwichensis, focusing on signals that precede physical attack against territorial intruders. We simulated intruders using song playback and taxidermic models, and we determined which behaviours were associated with physical attack. Previous studies that have used this approach suggest that many species produce songs of dramatically lower amplitude, or \“soft songs,\” as signals of aggressive intention. Savannah Sparrows, however, are not known to produce soft songs, and therefore, they provided an interesting system for testing signals that predict attack. Of 93 playback subjects, 23 males attacked the simulated intruder and 70 did not. To our surprise, Savannah Sparrows produced soft songs, and the number of soft songs was a significant predictor of attack on the simulated intruder. Birds also showed a nonsignificant tendency to produce more \“chip\” calls prior to attack on the simulated intruder, whereas three other measured behaviours (aggressive calls, wing waving and passes over the model) did not predict attack. Our study contributes to the growing body of research on aggressive territorial signals and reveals that soft song is an even more widespread signal of aggression in songbirds than previously recognized.

}, keywords = {aggressive signalling, animal communication, low-amplitude vocalizations, Savannah Sparrows, soft songs}, doi = {10.1111/eth.2018.124.issue-1010.1111/eth.12805}, url = {http://doi.wiley.com/10.1111/eth.2018.124.issue-10}, author = {Moran, Ines G. and Doucet, St{\'e}phanie M. and Newman, Amy E. M. and Ryan Norris, D. and Mennill, Daniel J.}, editor = {Koenig, W.} } @article {52569, title = {Male territorial aggression does not drive conformity to local vocal culture in a passerine bird}, journal = {Ethology}, volume = {123}, year = {2017}, month = {Jan-11-2017}, pages = {800 - 810}, abstract = {

In many songbird species, young individuals learn songs from neighbors and then settle nearby, thus creating neighborhoods of conformity to local vocal culture. In some species, individuals appear to postpone song learning until after dispersal, possibly to facilitate conformity to local dialects. Despite decades of study, we still lack a consensus regarding the selective pressures driving this delayed song learning. Two common hypothetical benefits to conformity, and thus delayed song learning, are rooted in territorial interactions; individuals preferentially produce local song either to avoid detection as new arrivals (deceptive mimicry) or to be more effectively recognized as conspecific territory holders. The dickcissel (Spiza americana) is an ideal species in which to study these hypotheses. Males of this species appear to delay song learning until they arrive at their first adult territory, each individual sings a single song type, and conformity to the local song culture is high. Using playback, we contradicted both of the territorial hypotheses described above; male dickcissels did not respond differentially to local vs foreign song playback treatment. We are confident in this lack of difference because dickcissels clearly responded less strongly to a third treatment, neighbor song, than to the other two treatments, demonstrating sufficient power in our experimental design (and providing the first evidence of the dear-enemy effect in dickcissels). Our results raise the question of why dickcissels respond equally aggressively to both local and foreign songs when other bird species often show reduced aggression toward foreign song. If reduced aggression to foreign song is not ubiquitous in species that achieve conformity through delayed learning, then selection from aggressive territorial interaction seems unlikely to be a general explanation for such delayed learning. Reduced aggression in response to foreign songs in other species may be due to reduced exposure to the stimulus of foreign song or to different cost-benefit trade-offs when responding to songs that deviate from the local average.

}, doi = {10.1111/eth.2017.123.issue-1110.1111/eth.12648}, url = {http://doi.wiley.com/10.1111/eth.2017.123.issue-11}, author = {Parra, Marcelina and Dalisio, Anthony C. and Jensen, William E. and Parker, Timothy H.}, editor = {Koenig, W.} } @article {52568, title = {Variation in chick-a-dee calls of bridled titmice ( Baeolophus wollweberi): Frequent use of non-combinatorial calls in a combinatorial calling system}, journal = {Ethology}, volume = {123}, year = {2017}, month = {Jan-11-2017}, pages = {835 - 842}, doi = {10.1111/eth.2017.123.issue-1110.1111/eth.12657}, url = {http://doi.wiley.com/10.1111/eth.2017.123.issue-11}, author = {Jung, Hwayoung and Freeberg, Todd M.}, editor = {Koenig, W.} } @article {52563, title = {Do birds differentiate between white noise and deterministic chaos?}, journal = {Ethology}, volume = {123}, year = {2017}, month = {Jan-12-2017}, pages = {966 - 973}, abstract = {

Noisy, unpredictable sounds are often present in the vocalizations of fearful and stressed animals across many taxa. A variety of structural characteristics, called nonlinear acoustic phenomena, that include subharmonics, rapid frequency modulations, and deterministic chaos are responsible for the harsh sound quality of these vocalizations. Exposure to nonlinear sound can elicit increased arousal in birds and mammals. Past experiments have used white noise to test for effects of deterministic chaos on perceivers. However, deterministic chaos differs structurally from white noise (i.e., random signal with equal energy at all frequencies), and unlike white noise, may differ dramatically depending on how it is produced. In addition, the subtle structural variation of chaos may not be distinguishable in the environment due to the attenuation and degradation of sound over distance and different habitat types. We designed two experiments to clarify whether American robins (Turdus migratorius) and warbling vireos (Vireo gilvus) discriminate between white noise and deterministic chaos. We broadcast and re-recorded white noise and two exemplars of deterministic chaos\—one generated with a Chua oscillator and the other generated using a logistic equation\—at 1, 10, 20, 30, 40, and 80 m across open and forested habitat and used spectrogram correlations to compare stimuli along this degradational gradient. We found that sounds degraded similarly in both habitats when compared to a reference distance of 1 m. Comparing pairs of stimuli across distances suggested that Chua chaos was more easily distinguishable from noise and logistic chaos. In addition, all stimuli became more distinctive over increased distance. The second experiment tested behavioral responses of robins and warbling vireos to control sounds of tropical kingbird (Quiscalus mexicanus), white noise, and two exemplars of deterministic chaos (Chua and logistic). Neither American robins nor warbling vireos responded differently to at least two types of deterministic chaos and white noise, validating previous playback studies that used white noise as a surrogate for deterministic chaos. Uniform responses to a variety of nonlinear features in these birds possibly reflect error management in alarm signal detection.

}, doi = {10.1111/eth.2017.123.issue-1210.1111/eth.12702}, url = {http://doi.wiley.com/10.1111/eth.2017.123.issue-12}, author = {Blumstein, Daniel T. and Whitaker, Jessica and Kennen, Judith and Bryant, Gregory A.}, editor = {Koenig, W.} } @article {50506, title = {Responses of male cricket frogs ( Acris crepitans) to attenuated and degraded advertisement calls}, journal = {Ethology}, volume = {123}, year = {2017}, month = {Jan-05-2017}, pages = {357 - 364}, abstract = {

We examined the vocal and non-vocal responses of male cricket frogs (Acris crepitans) to conspecific advertisement calls that had been attenuated or degraded by reducing the depth of amplitude modulation (AM). Both are characteristic of changes to the call as it is transmitted through natural habitats. As stimulus calls became more intense or less degraded, male cricket frogs gradually decreased their call rate and increased the number of call groups and pulse groups in their calls, changes indicative of increased aggressive interactions. At the higher intensities and lower degradation levels, the probability that males would shift to one of two non-vocal behavioral responses, attacking the perceived intruder or ceasing calling and abandoning the call site, gradually increased. The results show that differences in signal attenuation and AM degradation levels are perceived by males and trigger both vocal and non-vocal behavioral responses consistent with their use in evaluating the distance to a challenging male. Furthermore, the results indicate that the male responses are graded, increasing as intensity rises and degradation falls, and hierarchical, with vocal responses preceding behavioral responses over the range of intensities and degradation levels presented.

}, keywords = {acoustic communication, aggression, amphibians, cricket frogs}, doi = {10.1111/eth.2017.123.issue-510.1111/eth.12602}, url = {http://doi.wiley.com/10.1111/eth.2017.123.issue-5}, author = {Venator, Kurt R. and Michael J. Ryan and Wilczynski, Walter}, editor = {Koenig, W.} } @article {50491, title = {Sexual differentiation and seasonal variation in response to conspecific and heterospecific acoustic signals}, journal = {Ethology}, volume = {123}, year = {2017}, month = {Jan-06-2017}, pages = {460 - 466}, abstract = {

Interspecific territoriality is frequently reported between closely related species; however, few studies have demonstrated interspecific territoriality between distantly related species living in sympatry. We conducted playback experiments to investigate territorial behaviour in male and female White-bellied Wrens (Uropsila leucogastra) in response to simulated conspecific and heterospecific intruders during the breeding and non-breeding seasons. We explored whether heterospecific songs of the Happy Wren (Pheugopedius felix), a distantly related species and ecological competitor, elicited antagonistic responses from focal White-bellied Wrens, and whether such responses differed between the sexes. We also examined whether male and female responses to conspecific and heterospecific rivals varied with season. We found that male White-bellied Wrens always responded to conspecific song, and responded significantly more to heterospecific song compared to a control stimulus (Tropical Parula, Setophaga pitiayumi). In contrast, although female White-bellied Wrens responded strongly to conspecific song, their response to heterospecific song did not differ significantly from the control stimulus. The proportion of males that responded to heterospecific songs and the proportion of females that responded to conspecific songs varied seasonally, showing significantly lower responses during the breeding season. The intense responses of male White-bellied Wrens to playback of heterospecific songs suggest that they recognise ecological competitors based on their vocal signals. Furthermore, the decrease in agonistic interactions during the breeding season is in line with the hypothesis that aggressive behaviour may be detrimental to reproductive and parental activity, and the hypothesis that heterospecific animals pose less of a threat during the breeding season.

}, doi = {10.1111/eth.12616}, url = {http://doi.wiley.com/10.1111/eth.12616}, author = {Sosa-L{\'o}pez, J. Roberto and Mennill, Daniel J. and Renton, Katherine}, editor = {Koenig, W.} }