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Bird Ringing for Science and Conservation
Bird ringing in evolutionary and behavioural
studies
When competition between species of Darwin‘s
finches in the Galápagos archipelago is magnified during
periods of drought, Medium Ground Finches with smaller beaks have
less overlap in their food spectrum with the much bigger Large Ground
Finch than their bigger conspecifics. Thus, those Medium Ground
Finches carrying genes that cause them to have smaller bills survive
better and will have more descendants in the next generation. Consequently,
the frequency of the genes causing smaller beaks will increase in
this population. Evolution has
occurred.
Since it is individuals, and not populations, that
carry the genes, an in-depth understanding of evolution is rarely
possible without studying individuals. This, however, requires that
individuals can be recognized and followed over a period of time,
ideally over their entire lifespan. Individual identification is
particularly straightforward in birds through the use of a combination
of metal and coloured rings. To no small extent, the widespread
ringing of birds is the main reason why birds are the best studied
vertebrates in evolutionary biology.
Mating patterns are one important trait that affects
evolution. If certain birds have an opportunity to mate, while others
do not, a change of gene frequencies will also occur. Thus, the
study of animal behaviour underlying mate choice decisions and other
crucial behavioural traits is central to a better understanding
of evolution in natural populations. Again, only data from individually
recognizable animals can help us answer some of these questions.
Inbreeding, the mating of relatives, for example, has long been
an issue of great interest among animal and plant breeders. How
often does inbreeding occur in the wild and what are its consequences?
When birds of one population are individually colour-ringed for
many years, we can construct pedigrees that allow us to infer the
degree of inbreeding and thus its causes and consequences. On a
small island in Canada, for example, Song Sparrows have been shown
to mate with a relative as often as expected by chance. Thus, Song
Sparrows do not seem to avoid mating with relatives, despite the
fact that inbreeding considerably reduces reproductive success and
survival.
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The Alpine Chough is a social bird living
in high mountain areas. Though highly gregarious, ringing
and colour-ringing of this confiding species not only provided
insights into home range and population structure, but also
allowed to study individual foraging strategies. |
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In a population of European Dippers in Switzerland,
one female paired up with her son which himself had originated from
a pairing between her and her brother. On the other hand, one male
of these Cinclus c. aquaticus was resighted in Poland, mated to
a dipper that had been ringed in Sweden as a C. c.cinclus. It is
difficult to conceive of more opposite mating patterns among individual
birds from the same population.
The Dipper. Colour ringing has shown that
this attractive species
can sometimes be infanticidal and incestuous.
Some of the most interesting behaviours are those
that appear at first to contradict simple evolutionary explanations.
One such behaviour is infanticide which has been described in a
small number of bird species including the European Dipper. Why
would male Dippers kill young in nests of other pairs in the population
when they do not seem to have anything to do with that nest? At
first sight, one is tempted to explain such occurrences as aberrant
behaviours. However, an alternative, evolutionary explanation is
that the infanticidal males are killing the young so that the females
will lay a new clutch which could be fathered by the infanticidal
male. Observations of individually colour-ringed birds combined
with genetic analyses have the potential to resolve this and many
other fascinating questions in modern biology.
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