Charles Darwin was puzzled about the naivety of a marine iguana (Amblyrhynchus
cristatus), which he repeatedly tossed into the sea and which
did return to shore again and again, next to where Darwin was standing
and watching the animal. He knew that marine iguanas can swim perfectly
[watch Video], and
thus he expected the animal to escape ["...and as often as I
threw it in, it returned in the manner above described...Perhaps this
singular piece of apparent stupidity may be accounted for by the
circumstance, that this reptile has no enemy whatever on shore...",
Charles Darwin in Journal of Researches
]. The
observation that animals on islands do not run away from people became
legendary as "tame behavior" and has been attributed to the lack of
terrestrial predators. Unfortunately, times changed. Domestic cats and
dogs had been introduced on some of the islands in the archipelago,
which grew wild and built feral populations of novel predators, killing
numerous native animals. As potential additional disturbance, over
100.000 tourists annually flock the colonies of marine iguanas. When a
predator or human being approaches an animal, it usually flees as soon
as the threat gets too close. This flight distance is very short in
island animals.
The perception of an imminent threat causes an immediate physiological
stress response in animals at the continent, i.e. those, which always
experienced predators during their phylogenetic development. The heart
beat accelerates, the blood pressure increases. If
the threat is not over quickly, or if the predator continues its
pursuit,
additional stress hormones (corticoids) are secreted. which persist in
the body for a longer time. Stress hormones regulate the mobilization
of energy and prepare the body for increasing physical demands.
Animals native to Galápagos, which do not flee or do flee too
late from approaching humans or dogs, don't seem to correspond with
this
general pattern of anti-predator behavior, as outlined above.
Therefore, we ask whether
these island animals demonstrate reduced physiological stress responses
and to
what degree they can regain the ability to respond adequately to the
novel threat of introduced cats and dogs.
As part of our project we quantify flight initiation distances, i.e.
the distance at which animals start to run away from an approaching
human being. We also measure the physiological
parameters of a stress response and compare sites at which animals are
prone to predation by cats and dots with sites at which none of these
predators are present. In February 2005, one stretch of coast
at the island of San Cristobal has become tragically known for dog
aggression which virtually wiped out a population of marine iguanas (see photos). We took blood
samples for hormone analysis from a certain area, where dead
bodies and live marine iguanas lie alternatingly on the coastal rocks,
and predation threat could not have been more imminent.
Stress hormones, when elevated for a continued time period, can
suppress the immune system. This relationship is another topic in of
our studies, where we try to find answers to questions from basic
research as well as applied conservation biology.