at irst. However, they eventually become used to the sound
and may no longer consciously detect it.
Habitation may be one explanation for the tameness of our
city swans, but we were interested in exploring a different idea:
that wariness of humans differs among individual swans, and
those that can’t tolerate humans don’t settle in our cities.
Past research on other animals has indeed revealed that indi-
vidual animals differ consistently in certain behaviours, such as
fear, aggressiveness or novelty-seeking. Therefore, similar to
individual personalities in humans, some swans may be more
tolerant of potentially-threatening stimuli such as people while
others are much more wary, avoiding such stimuli wherever
possible. If this turned out to be the case, we guessed that these
individual differences may partly be under genetic control and
that swans hatched with a “wary” personality are more likely to
settle in areas where fewer people occur.
Our irst task in inding out whether fearful swans lee our
cities was to test the idea that city swans are indeed tamer than
their country-dwelling counterparts. We therefore measured
wariness towards humans among swans at a city lake in
Melbourne, and another at a sewage treatment plant where
there are few people.
We measured wariness using a metric known as the light initi-
ation distance: the distance at which an animal escapes an
approaching threat. We found that city swans are indeed less wary
of humans, typically waddling away from our approaches when
we came to within 13 metres. In contrast, the country swans could
only tolerate us when we stayed an average of 96 metres away.
This difference could either arise due to habituation of the
swans at the city lake or a preference of wary swans for quieter
wetlands. If the latter is true, we’d expect swan wariness to be
at least partly under genetic control, as occurs in both humans
and other animals.
We therefore asked whether variation in the wariness of
swans was related to individual differences in their genes. A
likely candidate gene was DRD4, which synthesises a neural
receptor for dopamine, a neurotransmitter involved in a wide
array of behaviours including fear, novelty-seeking and addic-
tion. Previous research has shown that a certain variant of the
DRD4gene is related to the tendency of some people to be
extroverted and the need to constantly seek new experiences.
Research has shown that this gene is involved in inluencing
diverse processes in animals as well, such as fear in dogs and
exploration of new environments in birds.
The DRD4gene was therefore an obvious irst place for us
to look. During our research we had regularly captured the
swans at both sites, which meant that we were able to take small
samples of blood containing the DNA of the swans. We could
therefore run some genetic analyses to isolate the DRD4gene
in each swan and read its DNA sequence.
We found that the vast majority of swans possessed one
particular variant of theDRD4gene. Swans with this variant
had much shorter light initiation distances (8 metres) than
those with rarer variants (14 metres).Thus swans with the
commonDRD4variant were more tolerant of humans than
other swans.This suggested that the warinessof swans towards
humans is indeed at least partly under genetic control.
Although these results were exciting, the icing on the cake
was our discovery that swans carrying the wary variant were
much more common at the sewage treatment plant.This
supports our contention that wary swans are preferentially
settling in quieter areas.
So a possible scenario may run like this.Two swanshatch at
a city lake, one with the boldDRD4variant and the other with
the wary variant. It would pay the bold swan to stay where it is:
city birds are often fed by humans, so food may be abundant here.
The survival and breeding successof birds is also often greater
in cities due to the lower number of predators found there.
However, the wary swan may rapidly become stressed if it
remains within the city. It therefore lies off to ind a quieter area
to live in.Theobserved difference in wariness between city and
country swans may therefore arise.
But things are never simple.Our comparison oflight initia-
tion distances between the city and country sites showed a differ-
ence of 83 metres, yet swans with the waryDRD4variant escaped
our approaches only 6 metres sooner than more tolerant swans.
A lot of variation in wariness therefore remains unaccounted for.
One likelyexplanation is that genes rarely function alone, and
multiple genes are likely to inluence a swan’s wariness towards
humans. In addition, habituation is probably also playing a
large role in reducing the wariness of city swans to people.
Can this information aid in the conservation of the black swan
and other species? It probably can.Our researchsuggests that
some individual birds are better able to cope with high levels of
human disturbance, and that this is partly under genetic control.
Thisinformation could be very useful for captive breeding
programs. Captive-bred individuals earmarked for release in
areas close to higher densities of humans could be selected based
on their genetic makeup and ability to survive in such envi-
ronments.This is beneicialfrom both a conservation and
animal welfare perspective.
So next time you feed the birds at your local park, take some
time to consider their individual personalities and the journey
they may have been through to arrive at your park.
Wouter van Dongenis a research scientist at Victoria University in Melbourne.JUNE 2016|| 35... swans hatched with a “wary”
personality are more likely to settle
in areas where fewer people occur.