John,
I perfectly agree that mortality is often a matter of chance. Sadly, the
demise of breeding populations such as these may depend on factors that
originate from our own misconduct through, for example, overfishing or
introduction of predators such as foxes.
We might assume that wild populations are resilient to natural disasters to
some extent but the implications of an event such as the hail storm for
population survival and conservation are much wider than just the event
itself. Another topical example would be the bush fires which if Australia
was still blanketed in forest may not be expected to be such a severe threat
to most native wildlife.
I therefore agree that respite from disturbance and good habitat are both
important factors in breeding success. But if this colony was to have been
left alone unstudied and unmanaged, then arguably the colony would have been
in a much worse state than it is as a result of predation. Encroachment of
sand onto a colony may also be considered a problem: another natural threat
that may have to do with human land-use elsewhere. Even if it does not, then
a single colony may represent the only available habitat as a result of
other coastal habitat having been degraded.
However you look at it, this event was unfortunate. If the productivity of
the site was stable or increasing annually before the event (maybe someone
can confirm this) there is no real reason to suspect that bird-banding for
research purposes was having a significant negative impact on the colony. As
an example, there is a site in NSW at Towra island which undergoes intensive
management and bird-banding where the population has been steadily
increasing (http://ssec.org.au/towra/html/little_tern.html). There is also
plenty of evidence for example in the UK where the RSPB successfully manages
and studies Little Terns in East Anglia - although they suffer the same
problems with predation from foxes which can wipe out a colony in a single
night.
The reason why a large proportion of terns with bands were killed during the
hailstorm is simply to do with the fact that a large proportion of birds are
banded each year at the site and therefore they make up a significant
proportion of the colony. If no banding had taken place, the event would
still have resulted in the same mortality levels. I may be wrong but I would
guess that a large proportion of banded birds return each year to breed and
that some banded birds may have returned for many years.
I think it is clear that bird-banding did not in this case directly or
indirectly kill any Little Terns. There are reasons why bird-banding in some
cases may not be a good approach and for some species / situations it may be
best avoided. However, this does not seem to be a good example on which to
debate the issue when the knowledge-benefits that enable us to control
predation and protect the colony through proper management far outweigh the
potential threats from managed disturbance events for bird-banding and other
research purposes.
If we think it is important that Little Terns do not die out, then we need
to try to find out the best ways of making sure that they survive to breed.
The logical conclusion of minimising disturbance by pulling out is to allow
nature to take its course in which case I would think that Little Terns have
had their day.
Simon.
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