https://www.bou.org.uk/blog-gotanda-antipredator-behaviour-darwins-finches/
Can Darwin’s finches adapt to invasive predators and
urbanization?
Dr. Kiyoko Gotanda
University of Cambridge
Gotanda, K.M. Human influences on antipredator behaviour in
Darwin’s finches. J. Anim. Ecol.
 |
| A small ground finch in the Galapagos |
"All
of [the terrestrial birds] are often approached sufficiently near to be killed
with a switch, and sometimes, as I myself tried, with a cap or a hat."
-Charles Darwin in "The Voyage of the Beagle"
The Galapagos Islands are renowned for their biodiversity
and large numbers of endemic species, including the Darwin’s finches. When
Charles Darwin visited the Galapagos Islands back in 1835, he noted that land
birds could be approached near enough to toss a hat over the birds (Darwin 1860)!
These and other Galápagos
organisms evolved for millions of years in the absence of humans and mammalian
predators, and thus developed a remarkable naïveté to humans and their
associated animals.
Humans now have a permanent presence on the Galapagos and
with that comes a variety of influences. A major, contemporary threat is the introduction of non-native predators
(Fritts and
Rodda 1998; Low 2002) which is often correlated with
extinctions on islands (Clavero and
García-Berthou 2005; Sax and Gaines 2008; Clavero et al. 2009). House cats (Felis silvestris catus) are particularly problematic because
they can decimate bird populations (Lever 1994;
Nogales et al. 2004; Wiedenfeld and Jiménez-Uzcátegui 2008; Loss et al. 2013). Recently, humans have introduced
to the Galapagos Islands invasive house cats ( Phillips,
Wiedenfeld, & Snell, 2012) that opportunistically prey on land
bird species, including Darwin’s finches, which poses a major threat to the
biodiversity on the islands(Stone et al.
1994; Wiedenfeld and Jiménez-Uzcátegui 2008). The Galapagos National Park has
taken extreme conservation measures and successfully eradicated cats and rats
on some of the islands (Phillips et al.
2005, 2012; Carrión et al. 2008; Harper and Carrión 2011).
The second human influence is we have established permanent
human populations creating urban areas. The increase in urbanization can
have a strong effect on ecological and evolutionary processes (Alberti 2015;
Alberti et al. 2017; Hendry et al. 2017; Johnson and Munshi-South 2017). Urbanization
on the Galápagos Islands has rapidly increased from ~1000 permanent residents
to ~25,000 in just 40 years, presently distributed across four towns each on
four different islands (UNESCO 2010; Guerrero et al. 2017). We are already seeing the
impact of human habitats on behaviour in Darwin’s finches. Urban finches in the
largest town on the Galapagos, Puerto Ayora (permanent human population =
~12,000) have shifted their behaviour and now exploit human foods which has
changed the finches’ ecological niche (De León et al. 2018).
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| Figure 1. Map of the Galapagos Islands showing islands that vary in the presence, absence, or eradication of invasive predators. Islands in orange have invasive predators, islands in green are pristine, and islands in purple have had invasive predators eradicated. Islands that have the presence of invasive predators are also the islands with permanent human populations. |
So, how have Darwin’s finches adapted to these different
human influences? I wanted to know how the finches might be adapting to the
presence, absence, or eradication of invasive mammalian predators, and to
urbanization. Specifically, I was interested in their antipredator behaviour. To study this, I focused on flight
initiation distance (FID), the distance at which an individual flees an
approaching predator, and is a metric of fear.
 |
| An invasive house cat in the Galapagos |
On islands
that have invasive predators, the finches have adapted by increasing their
antipredator behaviour. What’s most interesting, though, is that on islands
where invasive predators had been successfully eradicated either 8 or 13 years
prior to my data collection, the increased behaviour has been maintained. This
suggests that the increased antipredator behaviour could be an evolved
adaptation. However, it could also be due to other things such as learned
behaviour or cultural transmission of the behaviour through the generations.
Either way, invasive predators can have a lasting effect on antipredator
behaviour in Darwin’s finches.
I also compared antipredator behaviour in urban and
non-urban populations of Darwin’s finches on all four islands that have
permanent human populations. I found that on the three islands with the three
largest human populations, antipredator behaviour was significantly less in
urban finches when compared to non-urban finches, likely due to habituation.
Furthermore, antipredator behaviour was lower than what I found on islands that
were pristine and had no history of any human influences.
 |
Figure 2. Flight initiation distance in finches in relation to the presence, absence, or eradication of invasive predators and between urban and non-urban populations of Darwin’s finches.
Thus, my study shows that Darwin’s finches are adapting their antipredator behaviour to different human influences. These findings can help us better understand how the presence and subsequent removal of predators can have lasting effects on antipredator behaviour, and that that urbanization, and the likely habituation of Darwin’s finches to the presence of humans and other large stimuli, can strongly counteract any effects of the presence of invasive predators.
Additional Readings:
References
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