title: How noisy does a noisy miner have to be? Amplitude adjustments of alarm calls in an avian urban 'adapter'.
abstract: BACKGROUND
  Urban environments generate constant loud noise, which creates a formidable challenge for many animals relying on acoustic communication. Some birds make vocal adjustments that reduce auditory masking by altering, for example, the frequency (kHz) or timing of vocalizations. Another adjustment, well documented for birds under laboratory and natural field conditions, is a noise level-dependent change in sound signal amplitude (the 'Lombard effect'). To date, however, field research on amplitude adjustments in urban environments has focused exclusively on bird song.
  
  
  METHODS
  We investigated amplitude regulation of alarm calls using, as our model, a successful urban 'adapter' species, the Noisy miner, Manorina melanocephala. We compared several different alarm calls under contrasting noise conditions.
  
  
  RESULTS
  Individuals at noisier locations (arterial roads) alarm called significantly more loudly than those at quieter locations (residential streets). Other mechanisms known to improve sound signal transmission in 'noise', namely use of higher perches and in-flight calling, did not differ between site types. Intriguingly, the observed preferential use of different alarm calls by Noisy miners inhabiting arterial roads and residential streets was unlikely to have constituted a vocal modification made in response to sound-masking in the urban environment because the calls involved fell within the main frequency range of background anthropogenic noise.
  
  
  CONCLUSIONS
  The results of our study suggest that a species, which has the ability to adjust the amplitude of its signals, might have a 'natural' advantage in noisy urban environments.
authors.affiliation: School of Biological Sciences, Monash University, Clayton, Victoria, Australia. Helene.Lowry@monash.edu
authors.forename: Hélène
authors.initials: H
authors.lastname: Lowry
authors.forename: Alan
authors.initials: A
authors.lastname: Lill
authors.forename: Bob B M
authors.initials: BB
authors.lastname: Wong
mesh_terms: D000220:Adaptation, Biological / Q000502:physiology*; D000818:Animals; D004455:Echolocation / Q000502:physiology; D017753:Ecosystem; D004924:Escape Reaction / Q000502:physiology; D005239:Fear / Q000502:physiology; D006802:Human Activities; D006801:Humans; D009622:Noise / Q000009:adverse effects; D046109:Passeriformes / Q000254:growth & development / Q000502:physiology*; D013016:Sound / Q000009:adverse effects; D014506:Urban Renewal; D014828:Vocalization, Animal / Q000502:physiology*