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Click here to listen to an example of
rural song.
Click here to listen to an example of
urban song.
Many birds respond strongly to song of their own
species when it is played back to them over a loudspeaker in their
territory. They fly towards the source of the sound, hop around
nearby, sing at the loudspeaker and may even peck at it. The picture on the right shows a great tit peering down
a tree trunk at a tape recorder beneath which is playing the song of another great tit.
Only the male great tits
sing. But females judge males on the quality of their singing.
One aspect of their song is its pitch: females prefer lower pitched
song. So, what happens when the males raise their pitch in noisy
areas?
Our research
is investigating the differences in
pitch in relation to background noise on both a small and large scale.
In a study of 20 cities across the UK, we have recently found that great
tits sing at a significantly higher pitch in noisy urban areas than they
do in quieter rural ones (Mockford & Marshall
2009).
We
are also interested in the response of birds to songs sung at a pitch
different to their own. Computer editing songs and playing
them back to other birds allows us to observe any variations in response.
We have found that birds from noisy areas respond less strongly
to the song of birds from quieter areas. And vice versa, even when
the songs we play them
come from an area in the same city just a mile or two away (Mockford &
Marshall 2009). Since great tits can disperse up to 3km (1.8
miles) in their first year, this means that young urban males may have
difficulty establishing a territory or attracting a mate if they move to
an area with more or less noise than they are used to.
We are currently continuing our investigations of these
variations in response to noise-adapted song and the implications these
changes have on great tits' ability to communicate and breed
successfully.
Why is this important? Noise
has the potential to affect not only communication among members of a
single species but between species. If great tits cannot
communicate efficiently, it may disrupt their breeding: it may reduce a
male's ability to attract a female, or his ability to defend his
territory against other males.
 Such a behavioural barrier to breeding has
implications for how urban and rural birds interact - will they
eventually stop recognising each other? Will geneflow be reduced
between the urban and rural populations? What will happen in small
cities with small populations - will they suffer from genetic
bottlenecks?
These are speculative questions for the moment -
further research is required to understand the consequences - for
example, it is generally thought that great tits learn their song in
their first year and can only make small changes after this. The
extent of their ability to make changes could be crucial in terms of
their ability to adapt to noise levels in the areas to which they
disperse to breed.
Communication is also important between
different species of bird: not hearing an approaching predator, such as
a sparrowhawk, could have disastrous consequences for the individual
concerned. Similarly, noise may disrupt a predator's ability to
locate prey. No prey means no food which may mean a reduced ability to
survive in urban or noisy environments.
While some species (the urban survivors) may
be able to adapt to anthropogenic (man-made) noise, the decline of those
species that can’t adapt may decrease biodiversity around human
settlement. As mentioned above, one study in Germany found that
only high-pitched species lived next to main roads - low-pitched species
were simply not there.
And noise does not just affect birds.
Noise is important in the lives of mammals and amphibians too: from
croaking frogs to bats' ultrasonic navigation, to underwater
communication by marine mammals such as whales & dolphins.
In terms of Conservation, it is important to
conserve appropriate habitats, bearing in mind that air, light and noise
pollution are all important ecological factors.
These are just a few examples - man-made
noise has a wide impact on the natural world. Ongoing research
here and elsewhere seeks to improve our understanding of its
consequences. |
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