SUMMARYSound plays an important role in the life of many animals, including many bird species. Typically, male birds sing to defend a territory and to attract mates. Ambient noise may negatively affect the signal efficiency of their songs, which may be critical to reproductive success. Consequently, anthropogenic noise may be detrimental to individual birds and to populations in cities and along highways. Several bird species that are still common in urban areas have been shown to sing at higher frequency at locations where there is more low-frequency traffic noise. Here we show that chiffchaffs along noisy highways also sing with a higher minimum frequency than chiffchaffs nearby at a quiet riverside. Furthermore, through experimental exposure to highway noise we show that these birds are capable of making such adjustments over a very short time scale. The first 10 songs sung during the noise exposure revealed an immediate shift to higher frequencies, with a return to pre-exposure levels in recordings without noise the following day. In a transmission re-recording experiment we tested the impact of a potential measurement artifact by recording playback of the same songs repeatedly under different controlled noise conditions. We found an upward shift in the minimum frequency measurement associated with more noisy recordings of the same song, but this artifact was not of a scale that it could explain the noise-dependent spectral shifts in chiffchaffs.

Auditory sensitivity in fish serves various important functions, but also makes fish susceptible to noise pollution. Human-generated sounds may affect behavioral patterns of fish, both in natural conditions and in captivity. Fish are often kept for consumption in aquaculture, on display in zoos and hobby aquaria, and for medical sciences in research facilities, but little is known about the impact of ambient sounds in fish tanks. In this study, we conducted two indoor exposure experiments with zebrafish (Danio rerio). The first experiment demonstrated that exposure to moderate sound levels (112 dB re 1 μPa) can affect the swimming behavior of fish by changing group cohesion, swimming speed and swimming height. Effects were brief for both continuous and intermittent noise treatments. In the second experiment, fish could influence exposure to higher sound levels by swimming freely between an artificially noisy fish tank (120–140 dB re 1 μPa) and another with ambient noise levels (89 dB re 1 μPa). Despite initial startle responses, and a brief period in which many individuals in the noisy tank dived down to the bottom, there was no spatial avoidance or noise-dependent tank preference at all. The frequent exchange rate of about 60 fish passages per hour between tanks was not affected by continuous or intermittent exposures. In conclusion, small groups of captive zebrafish were able to detect sounds already at relatively low sound levels and adjust their behavior to it. Relatively high sound levels were at least at the on-set disturbing, but did not lead to spatial avoidance. Further research is needed to show whether zebrafish are not able to avoid noisy areas or just not bothered. Quantitatively, these data are not directly applicable to other fish species or other fish tanks, but they do indicate that sound exposure may affect fish behavior in any captive condition.

BackgroundBirdsong and human vocal communication are both complex behaviours which show striking similarities mainly thought to be present in the area of development and learning. Recent studies, however, suggest that there are also parallels in vocal production mechanisms. While it has been long thought that vocal tract filtering, as it occurs in human speech, only plays a minor role in birdsong there is an increasing number of studies indicating the presence of sound filtering mechanisms in bird vocalizations as well.Methodology/Principal FindingsCorrelating high-speed X-ray cinematographic imaging of singing zebra finches (Taeniopygia guttata) to song structures we identified beak gape and the expansion of the oropharyngeal-esophageal cavity (OEC) as potential articulators. We subsequently manipulated both structures in an experiment in which we played sound through the vocal tract of dead birds. Comparing acoustic input with acoustic output showed that OEC expansion causes an energy shift towards lower frequencies and an amplitude increase whereas a wide beak gape emphasizes frequencies around 5 kilohertz and above.ConclusionThese findings confirm that birds can modulate their song by using vocal tract filtering and demonstrate how OEC and beak gape contribute to this modulation.

Within the Anseriformes, the Anatinae (ducks) shows a wide variation in diet and feeding mechanisms, in contrast to the Anserinae (geese and swans). While grazing is common in the Anserinae, only few species within the Anatinae use terrestrial grazing as their main feeding mechanism (e.g., wigeons). This may be explained by conflicting functional demands of grazing and filter-feeding on the trophic system. In this study, the feeding performance, feeding mechanisms and oropharyngeal anatomy is compared between geese, wigeon and a general filter-feeder/pecker, the mallard (Anas platyrhynchos). The results show that the functional demands of filter-feeding and grazing are conflicting: filter-feeding requires a bald palatal surface and under-tongue transport for optimal functioning of the lingual cushion as a piston, whereas the transport mechanism of grazing requires large maxillary spines and over-tongue transport to retain grass during tongue protraction. The oropharyngeal anatomy of the wigeon shows a compromise in the small size of the maxillary spines that enable a sliding mechanism for the transport of a limited amount of grass. Filter-feeding is sometimes considered as a key adaptation that led to radiation in the anseriforms (Olson and Feduccia, 1980; Lack, 1974). We suggest, as an alternative hypothesis, that feeding on water plants may have led to the evolution of ridge-like structures in the bills, a sliding mandibular joint and the use of a water flow through the oropharynx (tongue pro- and retractions) for food transport in early anseriforms (cf. geese). A selection pressure on filter-feeding resulted in a large increase in efficiency of this system by the introduction of under-tongue transport of food and water (repatterning of bill and tongue movements) that enables the simultaneous intake and transport of a suspension of food particles (cf. Anatinae, a.o. Aythya and Anas). Terrestrial grazing later evolved by the development of maxillary spines, and in the case of the wigeon, a secondary change from the under tongue transport mechanism to over tongue transport for the grazing and pecking mechanisms only.

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