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Dotted line squares highlight 20 s of song produced during the ascending and the level phases as used for acoustic analysis and playback; fine structure of the syllables produced in each phase is shown below (A and B) at higher scale for the song in the continuous line squares. The arrows indicate the transition between the song produced during the ascending, the level and the descending phase.
Source publication
Skylarks inhabit open fields and perform an aerial song display which serves as a territorial signal. The particularly long and elaborate structure of this song flight raises questions about the impact of physical and energetic constraints acting on a communication signal. Song produced during the three distinct phases of the flight - ascending, le...
Citations
... The geographical positions of birds were measured on the ground using Garmin Oregon 450 GPS receivers. Each point referenced the location above which the bird was singing in a level phase of a given flight (Linossier et al. 2013). In our study, Skylarks were not individually marked. ...
... The resulting spectrogram had a 244-Hz bandwidth at a sampling frequency of 47 Hz and a time resolution of 2.7 ms (Specht 2016). A syllable was defined as a continuous trace on the sound spectrogram or a group of continuous traces spaced out by less than 25 ms (Linossier et al. 2013). Fundamental measurement errors of frequency (particularly minimum frequency) manually extracted via cursor from spectrograms can easily result from song elements overlapping with background sounds, especially due to the low amplitude of certain song elements (Zollinger et al. 2012). ...
The rapid development of wind energy may have negative effects on bird populations, including collisions with turbines, displacement due to disturbance or habitat loss, indirect effects of reduced breeding success and barrier effects. This challenging conservation issue has gained a great deal of interest, but the noise generated by turbines has been largely overlooked. Here, we studied acoustic behaviour of Skylarks Alauda arvensis in relation to wind farm start-up to assess whether a change in song parameters can indicate a deterioration in the acoustic environment. We recorded territorial males displaying close to operating and non-operating turbines and at a control site without turbines. In the following breeding season, we undertook replications at the same sites, except that the non-operating turbines were now in operation. We found that Skylarks displaying at the wind farm were affected by wind turbine noise. Males singing close to operating wind turbines sang higher-frequency songs than males from a control site and those that displayed near non-operating turbines. In addition, an upward frequency shift in songs was observed when non-operating turbines started to operate in the consecutive season. We therefore conclude that the frequency shift observed did not result from turbine presence, but from the noise they started to generate. This shows that a change in song parameters may reliably and within a relatively short time indicate a significant deterioration of the acoustic environment as a consequence of wind farm start-up. This may help conservation biologists to identify species and populations that are particularly susceptible to wind farm noise.
... In the current paper we reanalyzed a dataset published earlier [8] using Avisoft SASLAB Pro. For this dataset we had previously selected one song recording with the highest signal-to-noise ratio for each context and each subject, and we had analyzed the first 40 s of the song corresponding approximately to the ascending phase of the flight [38]. Songs had been high-pass filtered (cut-off frequency: 1.4 kHz). ...
Background
Vocal performance refers to the ability to produce vocal signals close to physical limits. Such motor skills can be used by conspecifics to assess a signaler’s competitive potential. For example it is difficult for birds to produce repeated syllables both rapidly and with a broad frequency bandwidth. Deviation from an upper-bound regression of frequency bandwidth on trill rate has been widely used to assess vocal performance. This approach is, however, only applicable to simple trilled songs, and even then may be affected by differences in syllable complexity.
Results
Using skylarks (Alauda arvensis) as a birdsong model with a very complex song structure, we detected another performance trade-off: minimum gap duration between syllables was longer when the frequency ratio between the end of one syllable and the start of the next syllable (inter-syllable frequency shift) was large. This allowed us to apply a novel measure of vocal performance - vocal gap deviation: the deviation from a lower-bound regression of gap duration on inter-syllable frequency shift. We show that skylarks increase vocal performance in an aggressive context suggesting that this trait might serve as a signal for competitive potential.
Conclusions
We suggest using vocal gap deviation in future studies to assess vocal performance in songbird species with complex structure.
Electronic supplementary material
The online version of this article (doi:10.1186/s12915-014-0058-4) contains supplementary material, which is available to authorized users.
... In the current paper we reanalyzed a dataset published earlier [8] using Avisoft SASLAB Pro. For this dataset we had previously selected one song recording with the highest signal-to-noise ratio for each context and each subject, and we had analyzed the first 40 s of the song corresponding approximately to the ascending phase of the flight [38]. Songs had been high-pass filtered (cut-off frequency: 1.4 kHz). ...
Background
Vocal performance refers to the ability to produce vocal signals close to physical limits. Such motor skills can be used by conspecifics to assess a signaller¿s competitive potential. For example it is difficult for birds to produce repeated syllables both rapidly and with a broad frequency bandwidth. Deviation from an upper-bound regression of frequency bandwidth on trill rate has been widely used to assess vocal performance. This approach is, however, only applicable to simple trilled songs, and even then may be affected by differences in syllable complexity.ResultsUsing skylarks (Alauda arvensis) as a birdsong model with a very complex song structure, we detected another performance trade-off: minimum gap duration between syllables was longer when the frequency ratio between the end of one syllable and the start of the next syllable (inter-syllable frequency shift) was large. This allowed us to apply a novel measure of vocal performance ¿ vocal gap deviation: the deviation from a lower-bound regression of gap duration on inter-syllable frequency shift. We show that skylarks increase vocal performance in an aggressive context suggesting that this trait might serve as a signal for competitive potential.Conclusions
We suggest using vocal gap deviation in future studies to assess vocal performance in songbird species with complex structure.
... Their flight song and, thus, the song lasts, on average, for 261 s (Hedenström 1995) but can take up to 1 h (NG, personal observation). A song flight consists of three characteristic phases: the ascending flight; the level flight, which makes up the majority of the time spent in the air; and the descending flight (Hedenström 1995;Linossier et al. 2013). Skylarks have, on average, 341±21 different syllable types (Briefer et al. 2008). ...
In songbirds of the temperate zone, often only males sing and their songs serve to attract females and to deter territorial rivals. In many species, males vary certain aspects of their singing behavior when engaged in territorial interactions. Such variation may be an honest signal of the traits of the signaler, such as fighting strength, condition, or aggressive motivation, and may be used by receivers in decisions on whether to retreat or to escalate a fight. This has been studied intensively in species that sing discontinuously, in which songs are alternating with silent pauses. We studied contextual variation in the song of skylarks (Alauda arvensis), a songbird with a large vocal repertoire and a continuous and versatile singing style. We exposed subjects to simulated territorial intrusions by broadcasting conspecific song and recorded their vocal responses. We found that males sing differently if they are singing spontaneously with no other conspecific around than if they are territorially challenged. In this last case, males produced lower-frequency syllables. Furthermore, they increased the sound density of their song: they increased the proportion of sound within song. They seem to do so by singing different elements of their repertoire when singing reactively. Furthermore, they increased the consistency of mean peak frequency: they repeated syllable types with less variability when singing reactively. Such contextual variation suggests that skylarks might use low frequencies, sound density, and song consistency to indicate their competitive potential, and thus, those song features might be important for mutual assessment of competitive abilities.
Background: Vocal performance refers to the ability to produce vocal signals close to physical limits. Such motor skills can be used by conspecifics to assess a signaler's competitive potential. For example it is difficult for birds to produce repeated syllables both rapidly and with a broad frequency bandwidth. Deviation from an upper-bound regression of frequency bandwidth on trill rate has been widely used to assess vocal performance. This approach is, however, only applicable to simple trilled songs, and even then may be affected by differences in syllable complexity.
Ants are key model organisms in the study of navigation and memory formation. Many ants learn food locations very quickly and with high accuracy. But can individual ants learn multiple separate food locations, associate them with a cue, and then correctly recall the food location and navigate towards it when later presented with that cue? In this experiment, we sequentially trained Lasius niger foragers to two scented feeders at either end of a T-maze. The next day, an odour cue corresponding to one of the food sources was presented to the ants in the air, on the substrate and via trophallaxis with nest mates. Trained foragers accurately navigated to the correct side of the T-maze (89 % correct decisions), but only after the first 10 min of testing. This demonstrates the ability of ants to perform associative recall, forming clear associates between odour cues and food locations and using these associations to navigate to food sources. We also found that trained ants in the first 10 min of testing showed no preference for the correct side (57 % correct decisions), which may be related to the motivational state of the ants tested. Ants with different motivational states (whether they are ‘scouting’ or ‘recruited’) made use of route memories in a completely different manner. This highlights the importance of taking account of motivational states when performing behavioural experiments.
Reproductive delays between mating and birth may provide a previously unconsidered avenue for post-copulatory sexual selection in mammals. In particular, delayed fertilization could provide an enhanced opportunity for sperm competition by extending the time for ejaculates to interact in the female reproductive tract. We tested the prediction that species with delayed fertilization exhibit greater degrees of sperm competition than those without delays by examining testis volume (a proxy for sperm competition) in 38 species of bats. Examination of fluid-preserved museum specimens of bat species with and without delays revealed that species with delays (in particular those with delayed fertilization) had significantly larger testes than species without them. Although it predicts the presence of delayed fertilization, hibernation did not predict relative testis size. We conclude that, once they evolve, reproductive delays may facilitate sperm competition.
