Elsevier

Animal Behaviour

Volume 98, December 2014, Pages 27-33
Animal Behaviour

Silvereyes decrease acoustic frequency but increase efficacy of alarm calls in urban noise

https://doi.org/10.1016/j.anbehav.2014.09.026Get rights and content

Highlights

  • We sampled silvereye alarm calls from urban and rural habitats across Australia.

  • Urban alarm calls had lower-frequency profiles than rural calls.

  • These findings contrast with current literature on urban bird vocalizations.

  • We developed spectrographic noise profiles for urban and rural habitats.

  • The observed frequency shifts increased the active space of the calls by 20%.

Many passerines adjust song attributes to avoid potential masking by anthropogenic noise. The costs of masking should be particularly high for vocalizations important for survival (e.g. alarm calls), but few studies have investigated how such calls are affected. We compared urban and rural silvereye, Zosterops lateralis, alarm calls across southeastern Australia, and found that urban calls had lower average, peak and maximum frequencies than rural calls. The average, peak and maximum frequency of alarm calls also decreased linearly with increasing background noise. The direction of this frequency shift runs contrary to expectations and previous findings of higher-pitched avian vocal signals in urban habitats, including higher-pitched song and contact calls in urban silvereyes. However, assuming no change in call amplitude, acoustic modelling indicates that the observed frequency shift would lead to a 20% increase in the predicted active space of alarm calls (i.e. the distance over which the calls can be detected by a conspecific bird) in urban noise, and therefore may be potentially adaptive. Our findings highlight the importance of considering behavioural and ecological contexts in urban acoustic-adaptation studies.

Section snippets

Study Species

Silvereyes are common native Australian passerines that inhabit a variety of environments, including urban areas. Silvereye songs and contact calls in city environments are higher in pitch than those in rural habitats (Potvin et al., 2011). Silvereyes also utter alarm calls, which are broadband in nature and consist of a fundamental frequency and a number of emphasized harmonics (Fig. 1).

Study Sites

Each pair of study sites was located at the following specific geographical areas in southeastern Australia,

Noise Profiles, Masking and Active Space in Rural and Urban Habitats

Mean noise levels at urban sites were 9.0 dB (A) higher than those at rural sites (95% CI: 2.09, 15.94 dB (A)). The energy of this noise was also distributed differently across the frequency spectrum in the two habitats (Fig. 2a). Thus, the background noise in each habitat differed not only in intensity (i.e. calls needed to be louder in urban areas to overcome masking by the background noise) but also according to frequency (Fig. 2b). For instance, a call made at 2500 Hz in the urban habitat

Discussion

Across disparate geographical locations, alarm calls of silvereyes in urban areas had lower average, peak and maximum frequencies than those of rural birds. This pattern contrasts with our earlier finding of higher frequencies in the songs and contact calls of urban silvereyes (Potvin et al., 2011). It also contradicts the prevailing expectation from recent empirical studies that the vocalizations of urban birds should generally display upward frequency shifts to reduce masking from urban

Acknowledgments

We thank J. Kruckel for field assistance, G. Fry, A. Leishman, G. Clancy, A. Tarrant, D. Paton, D. Williams, E. Woehler, R. Fuller and A. Fletcher for assistance in locating/banding birds, and Australian National Botanic Gardens (ACT), Namadgi National Park (ACT), Glenorchy City Council (Tas), Brisbane City Council (Qld), Susan Island Trust (NSW), Munghorn Gap Nature Reserve (NSW), Camden Airport (NSW), Kogarah City Council (NSW), Darebin City Council (Vic) and Darebin Parklands Association

References (64)

  • E. McIntyre et al.

    Ambient noise and parental communication of predation risk in tree swallows, Tachycineta bicolor

    Animal Behaviour

    (2014)
  • H. McMullen et al.

    Anthropogenic noise affects vocal interactions

    Behavioural Processes

    (2014)
  • C.L. Pytte et al.

    Regulation of vocal amplitude by the blue-throated hummingbird, Lampornis clemenciae

    Animal Behaviour

    (2003)
  • H. Slabbekoorn et al.

    Cities change the songs of birds

    Current Biology

    (2006)
  • P.S. Warren et al.

    Urban bioacoustics: it's not just noise

    Animal Behaviour

    (2006)
  • A.V. Badyaev et al.

    Evolution on a local scale: developmental, functional, and genetic bases of divergence in bill form and associated changes in song structure between adjacent habitats

    Evolution

    (2008)
  • E. Bermudez-Cuamatzin et al.

    Experimental evidence for real-time song frequency shift in response to urban noise in a passerine bird

    Biology Letters

    (2011)
  • S. Blumenrath et al.

    Degradation of great tit (Parus major) song before and after foliation: implications for vocal communication in a deciduous forest

    Behaviour

    (2004)
  • G. Boncoraglio et al.

    Habitat structure and the evolution of bird song: a meta-analysis of the evidence for the acoustic adaptation hypothesis

    Functional Ecology

    (2007)
  • F. Bonier et al.

    Sex-specific consequences of life in the city

    Behavioral Ecology

    (2007)
  • H. Brumm

    Causes and consequences of song amplitude adjustment in a territorial bird: a case study in nightingales

    Annals of the Brazilian Academy of Sciences

    (2004)
  • G.C. Cardoso et al.

    Directional cultural change by modification and replacement of memes

    Evolution

    (2011)
  • C.K. Catchpole et al.

    Bird song

    (2008)
  • J.S. Clark

    Why environmental scientists are becoming Bayesians

    Ecology Letters

    (2005)
  • K.L. Evans et al.

    The effect of urbanisation on avian morphology and latitudinal gradients in body size

    Oikos

    (2009)
  • K.L. Evans et al.

    Colonisation of urban environments is associated with reduced migratory behaviour, facilitating divergence from ancestral populations

    Oikos

    (2012)
  • T.G. Forrest

    From sender to receiver: propagation and environmental effects on acoustic signals

    American Zoologist

    (1994)
  • C.D. Francis et al.

    Vocal frequency change reflects different responses to anthropogenic noise in two suboscine tyrant flycatchers

    Proceedings of the Royal Society B: Biological Sciences

    (2011)
  • A.P. Gavett et al.

    Blood constituents and their relation to diet in urban and rural house sparrows

    Condor

    (1986)
  • K. Gross et al.

    Behavioral plasticity allows short-term adjustment to a novel environment

    American Naturalist

    (2010)
  • M.L. Hall et al.

    Male songbird indicates body size with low-pitched advertising songs

    PLoS One

    (2013)
  • S. Hamao et al.

    Urban noise and male density affect songs in the great tit Parus major

    Ethology, Ecology & Evolution

    (2011)
  • Cited by (38)

    • Does anthropogenic noise affect the acoustic courtship interactions of Gryllus bimaculatus?

      2021, Animal Behaviour
      Citation Excerpt :

      Our results also highlighted significant differences in the acoustics produced by males under different acoustic conditions. Documented changes to acoustic signals under anthropogenic noise include changes in dominant frequency (Cunnington & Fahrig, 2010; Potvin et al., 2014; Shieh et al., 2012) and amplitude (Brumm & Todt, 2002; Spiga, 2016), as well as differences in the temporal (Costello & Symes, 2014; Díaz, Parra, & Gallardo, 2011) and spatial aspects (Caorsi, Both, Cechin, Antunes, & Borges-Martins, 2017; Chen & Koprowski, 2015) of signalling behaviour. In the present study, we observed differences in the tick rate (ticks/min), song escalation and the dominant frequency of courtship ticks, albeit mostly under white noise, not traffic noise.

    • The low-frequency acoustic structure of mobbing calls differs across habitat types in three passerine families

      2018, Animal Behaviour
      Citation Excerpt :

      Finally, there may be nonadaptive reasons for this pattern. One possible explanation is that song is generally learned whereas mobbing calls are considered innate (Benedict & Krakauer, 2013; Marler, 2004; Potvin et al., 2014). Thus, calls will take longer to evolve than song in response to changes in habitat, such as urbanization.

    • Anthropogenic noise alters dwarf mongoose responses to heterospecific alarm calls

      2017, Environmental Pollution
      Citation Excerpt :

      Alarm calling, the production of particular vocalisations to warn others of danger, is a key anti-predator strategy in many species (Klump and Shalter, 1984; Hollén and Radford, 2009). The few studies exploring the impact of anthropogenic noise on alarm-call behaviour have mostly considered conspecific communication, particularly how the acoustic parameters of the alarm calls themselves differ depending on noise conditions (Lowry et al., 2012; Potvin et al., 2014; Templeton et al., 2016), but also how responses may be disrupted (Rabin et al., 2006; McIntyre et al., 2014; Templeton et al., 2016). However, many animals are known to eavesdrop on heterospecific alarm calls, responding appropriately to warnings of danger and even the additional information often contained within such vocalisations (Magrath et al., 2015).

    View all citing articles on Scopus
    View full text