In reply to earlier postings, Dean Portelli wrote at length on bird dialects
- an interesting topic. As Dean points out, there is much we don't know
about dialects - e.g. do birds 'change their tune' at will, are they
influenced by their new neighbours, etc.
Some years ago I studied the territorial song dialects of Superb Lyrebirds
in my local area. Lyrebirds are weak fliers and do not travel long
distances, so were an ideal species for a study on vocalizations. In
certain rugged terrain the lyrebirds do tend to aggregate into distinct
populations and the males will all share the same dialect of territorial
song. Each population also seems to share the same suite of mimicked
sounds.
I was able to show that geographically and acoustically isolated populations
of Superb Lyrebirds had very distinctive dialects, and that those dialects
did not change over a period of many years, and that all the males in any
one group used the same dialect.
What I was unable to establish was whether or not any lyrebirds moved away
from their original birth-territory, to new areas. And if they did move on,
did they then adopt the territorial songs of the population they had moved
into?
My guess is that, perhaps driven by fire, land-clearing, or the biological
imperitive to widen the gene pool, some birds would indeed move away from
their original home territory and take up the songs of another area. The
only way to prove that would be to somehow tag individual birds, which is
probably not a good idea for the elusive lyrebirds given that there are so
many other pressures on them, drought, feral cats, foxes etc. (Local
lyrebird populations at nearby Mt. Airly seem to have plumetted over the
past ten years or so.)
Song variation in birds can indeed be shown on sonagrams - if you can hear a
difference then you will easily see it on a sonagram, and even if you can't
hear much difference, that difference will still show up on a sonagram.
Recording birdsong is a great way to learn about bird behaviour!
Vicki Powys
Capertee Valley NSW
on 8/5/03 3:23 PM, Dean Portelli at wrote:
> Hi All (esp Penn Gwynne),
>
> Keith Brandwood made earlier comment regarding bird dialects in commenting
> on Val Curtis' comments on geographical variation in Pied Currawong song.
> Firstly, the definition of dialects can be somewhat confusing as the term
> has been used to describe different forms of variation in vocalisations. One
> definition is that dialects are "population specific features in acquired
> vocal patterns" (Mundinger 1982, pp. 147-208 in Acoustic Communication in
> Birds Vol 2). The use of the term "population" in this definition further
> complicates the issue as population can be a difficult term to define in
> this context. It may not be surprising that there is much confusion and
> controversy over the definition of dialects. Variation in vocalisations when
> viewed across all different species probably represents a gradient (not
> necessarily a smooth one!), and the question becomes where do you place a
> line along this gradient that delineates what is and what is not regarded as
> a dialect. At one end of this gradient variation in vocalisations can be
> across large geographical areas where individuals within a geographical area
> sound remarkably similar but dramatically different from individuals of
> another geographical area (i.e. variation within < variation between). At
> the other end of the gradient local variation may be greater than any
> variation over a large geographical area; for example within a population
> there is a large amount of variation in the structure of a particular
> vocalisation (e.g. advertisement song) and when you take an individual from
> that population and analyse its songs you may not be able to identify which
> geographic locality it came from as the variation within a locality 'swamps'
> the variation that exists between localities (i.e. variation within = or >
> variation between). I think that the use of the term dialect is least
> confusing at the first end of the gradient that is described above (i.e.
> where variation within < variation between).
> Now, moving on (phew!). Keith asked if dialects would show up on a
> spectrogram (aka sonagram) - the answer is generally yes. If there is
> sufficient variation in the structure of the vocalisation between sites it
> will show up on a sonagram as a different looking picture of lines,
> squiggles, blurs etc that represent the particular sounds that comprise the
> vocalisation in a frequency vs time display (with relative amplitude
> indicated within the display). In fact, this is usually how the possible
> existence of dialects is investigated.
> Keith also suggested the possibility of using dialects to track migration
> and suggested that this may be much easier than banding. I agree that
> recording songs would be much much easier than the many hours that go into
> erecting nets in the hope of catching an already banded bird (hopefully from
> somewhere else other than the banding site!!!). However, what should be
> realised from the discussion above is that variation in vocalisations can be
> very complex, and may not be as simple as different geographic areas having
> a distinct vocalisation 'signature'. To attempt this with a migratory
> species much information on the vocal behaviour of the species must first be
> known, I will take the Yellow-Faced Honeyeater Keith mentioned as an
> example. Obviously the first question is to examine the pattern of variation
> in song across the range of the YFHE when it is not migrating so we can
> identify the 'source' of migrating birds (one possible problem we will
> encounter here is understanding what happens to the non-breeding YFHE, do
> they always return to the breeding grounds or do they move elsewhere? - this
> may be a complication), is there a distinct pattern of variation in
> vocalisations that is associated with geographical variation? is this
> variation great enough that we can confidently identify which locality any
> individual chosen at random came from if we can record its vocalisations?
> Another important aspect is an understanding of the ontogeny of the
> variation in vocalisations within the species, i.e. when do YFHE's acquire
> their song? is it within the first few months of life at the nesting site?,
> or is it during subsequent migration?, or at the non-breeding grounds?, or
> is the YFHE an open-ended learning species that retains the capacity to
> modify the structure of it's song throughout life? (as opposed to species
> with a restricted time window in which the structure of vocalisations is
> learnt and then crystallised for the rest of the individuals life, accepting
> possibly some slight modification). For example, it is known that for some
> species when birds move populations they adopt the distinct songs of the new
> population and drop their old songs, so if you were using vocalisations to
> monitor movements in these species you wouldn't detect the movement!! While
> this particular scenario may not apply to YFHE a similarly confounding
> scenario may. This last question basically addresses where the song came
> from and how constant are songs across an individual's life. If the YFHE can
> modify its song through life it may complicate our interpretation of results
> of possible geographical variation in song when trying to establish
> population movement (i.e. migration patterns). In addition, we need to
> examine the singing behaviour of the species at different times of the year.
> Do YFHE's sing the same song they do at their breeding grounds when they are
> on migration or at their non-breeding grounds? Or do they have different
> songs (if they sing throughout the year!) used at different times of the
> year? Undoubtedly there are many other questions of importance, but I think
> it is clear that there must be a strong knowledge base of the vocal
> behaviour of the species in question before there is any real possibility of
> using vocalisations to track movements. Perhaps, not much easier than
> setting up nets to catch birds!?!? It certainly would make an interesting
> long-term study! One that may even involve banding birds for individual
> identification.
>
> One last point: Penn Gwynne wrote "Keith, I'm worried about you my good
> friend? ask a bander to think? ". Well, Penn I myself am a bander. And I ask
> you this question: do you think the above discussion required any thought on
> my part?
>
> Cheers, Dean
>
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