How bird banding is used for research - re Little Tern disaster

To: "Marilyn Davis" <>, <>
Subject: How bird banding is used for research - re Little Tern disaster
From: "Simon Mustoe" <>
Date: Mon, 7 Jan 2002 15:28:43 +1100
Marilyn et al,

I understand your concerns to some extent about bird banding. I would rather
not discuss the ethical issues on this forum as I do not believe that it is
the place. However, I would like to point out that individual marking
studies do in fact have extremely important uses for research. For various
reasons individual tagging of birds is essential for detailed ecological
studies and to build up a picture of avian life histories. There is an
enormous amount of literature that highlights the importance of ecological
studies using individually marked birds. I would go as far as to say that
there is hardly a single academic researcher on the planet that does not use
some form of tagging or marking for ecological research.

Anyway, a little on the theory.

Shorebirds and seabirds like Little Terns for example have long life spans
and produce few offspring. They are also colony formers which makes them
both vulnerable to short term impacts but also easier to research.  The
perpetuation of a population will depend in part on the overall 'fitness' of
the breeding stock - a large proportion of seabird populations (as well as
many terrestrial populations) often exist as non-breeders waiting for the
opportunity to move in and take over when the fittest and strongest breeders
are displaced.

It is logical therefore to assume that these non-breeders are less fit and
healthy / strong than the breeders. It is equally true that there are
colonies which harbour individuals that are on average much healthier than
birds in other colonies - basically the strongest birds get the best

Establishing the relationship between birds and their habitat is the essence
of ecology but cannot always be achieved unless we can work out how bird
fitness effects the results. For example, area A of an intertidal estuary
may have twice as many birds as area B. However, unbeknown to researchers,
area B is host to very strong breeders whereas area A (which has many more
birds) has large flocks of young birds and birds that are diseased. Area B
therefore may be much more important for conservation even though the
results of a survey show otherwise. The only way to really tell how
important an area is, is to know how fit the birds are in each area. One way
that this may be done is by identifying the age of birds on plumage (if we
assume that young birds are less fit) - but this is not always possible if
plumages are alike. Another way is to colour ring individual birds and to
assess how successful they are in feeding or how many young they produce
each year. Over a few years perhaps we might find that a greater percentage
of birds in area B survive particularly harsh winters but we can only know
this if we can identify individuals.

Mortality events such as that which occurred on Tern Island will pose many
questions for conservationists that only bird banding / capture studies can
answer such as, how old and healthy were the birds that died and how
important were they in maintaining a high level of offspring each year.
Subsequently it may be possible to determine whether younger birds come in
to the colony to take over (these younger birds may be aged accurately if
they were banded as fledglings). An overall drop in the survival rate of
offspring may be determined from banding studies alone. Otherwise we can
tell if birds fledge successfully but not if they die days, weeks or months
later. For example, the Little Tern colony may have hypothetically produced
100 young in the year 2000 and from previous banding experiments we expect
30 young to return to breed two years later. This may indicate that about
70% die while reaching sexual maturity. If after this hail storm we discover
that the overall weight and age of birds attending the colony has diminished
we might expect the young that are produced to be less healthy and strong
than in previous years. Perhaps in 2004 only 10% of youngsters will return
to breed the following year. This information is only possible through
individually marking birds.

A non-avian example is northern Right Whales off the east coast of the
United States. These animals do not need to be marked as they have
individual head markings. However, studies of individually marked animals
and their offspring have led scientists to conclude that they are in a much
worse conservation predicament than could have been assumed otherwise. They
have been able to model projected survival rates and administer conservation
actions appropriately.

There is a great deal more that can be said on this topic and what I have
summarised is only a coarse series of examples. I hope they help.


Simon Mustoe.

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