Camouflage is often a matter of life or death in the wild.
This footage shows some clutches of eggs in Zambia and South Africa that have been spotted
by predators, such as this cat-like genet… or these banded mongooses, which were caught
on our motion-triggered cameras.
I’m Dr Jolyon Troscianko and I’m based at the University of Exeter in the Sensory
Ecology and Evolution group.
My research revolves around the fundamental bioscience of animal vision and signalling
– a field called sensory ecology.
Together with Jared Wilson-Aggarwal, I’m working on a project co-led by Dr Martin Stevens
at Exeter and Dr Claire Spottiswoode at the University of Cambridge, investigating how
camouflage works in the real world.
Studying camouflage has lots of practical applications – the military is the most
obvious, where being well hidden can also be a matter of life and death, but there are
many others.
Such as concealing ugly buildings, telegraph poles or mobile phone masts.
Then there is a long history of collaboration among biologists and artists in camouflage
work.
And of course a better understanding of camouflage can be turned on its head and used to help
make objects stand out from their background, as we might want to do in advertising or road
safety.
We use ground-nesting birds as our study system.
These birds rely their on camouflage to survive because they nest out on open ground where
a host of natural predators – like this cheeky vervet monkey – try to find and eat
their eggs.
We set up these cameras and captured this amazing footage to find out what the birds’
natural predators were.
We can then use special photographic techniques and computer models to simulate how different
predator species with different eyes and visual systems actually see these birds, to better
understand what aspects of the egg's or bird’s camouflage and background affect their survival.
But amazingly we still know very little about what types of camouflage are most important
in the wild and how they affect survival.
In the natural world, it’s very difficult to find a study system where you can link
predation with the effectiveness of an animal’s camouflage – partly because camouflaged
animals are so hard to find and keep moving all the time!
We chose to study ground-nesting birds because not only does their nest survival depend critically
on its camouflage, but also because their nests are vulnerable and open to passing predators
as they sit in the same spot for the few weeks it takes the eggs and chicks to develop.
We mainly use two groups of bird species with contrasting life strategies.
The first group, the nightjars, are ghostly birds that forage for insects on the wing
during the night.
During the day, they sit tight on the ground and are incredibly well camouflaged as you
can see, or perhaps not, as the camera zooms in… can you see the bird yet?
No?
There it is!
This is a fiery-necked nightjar.
As you can see they use their incredibly well camouflaged bodies to protect their eggs that
they lay directly on the ground, making no nest at all.
You can sometimes walk right up to them and they don’t flinch until you almost step
on them, within a metre or so.
In contrast, our second focal group – the plovers and coursers – run off as soon as
they spot a predator.
You can see that here, when the swimmers get too close to comfort for this three-banded
plover.
With no adult to protect, it the egg’s camouflage comes into its own – it’s the only thing
between life and death for the chicks developing inside.
When we find a nest we take photos using cameras in normal, visible light at 10 metres, 5 metres,
and at 2 metres.
Then depending on the species the bird flushes.
Here, you can see me lining up a control picture with a grey standard in the foreground, that’s
the little grey disc.
Even though we only took photos when it was sunny there are still big differences in lighting
depending on time of day and atmospheric dust and moisture.
This grey standard allows us to control for these lighting differences.
Then we take pictures of the eggs at one metre, as well as an aerial shot and a lower shot
to take in the views of different predators – circling birds versus stalking mongooses
for example – and to include different spatial scales.
In addition to normal light, we also take images in ultraviolet light, or UV.
In this UV photo picture of a Mozambique nightjar, the violet colour corresponds to parts of
the body that reflect UV light.
UV is light with very short wavelengths that the human eye can't see, but many other animals
such as many birds, mammals, reptiles and insects can.
Most humans are trichromatic, meaning we see the world in three colours – red, green
and blue, which is much the same as the Zambian vervet monkeys and baboons.
That's why the red, green and blue diodes on a TV computer screen are enough to reproduce
all the colours we can see.
But birds are probably tetrachromatic, seeing deep violet or ultraviolet in addition to
red, green and blue.
When we take a picture in UV we can convert this image into a view that other animals
would see, so we can analyse how eggs look from the perspective of a bird of prey, or
to a monkey or a mongoose.
The modelling is computer based, and to do it we need to know the sensitivity of the
camera and the animals’ eyes to different wavelengths of light.
Then we can convert the images across from camera vision to animal vision, to simulate
how the light receptors, or cones, in animals’ eye would detect the colour – even though
in the case of UV we can't imagine what that colour would look in an animal's brain.
This research requires knowledge of how visual systems work in different animals.
This is also why we needed the hidden cameras, so we’d know which predator’s vision to
simulate.
It’s therefore really important to know your camera inside out.
We take a lot of time calibrating our equipment and writing new software to undertake our
modelling of vision.
When analysing the images we use our custom software to quantify the egg's colours and
patterns, then and compare them to the background at lots of different scales.
This way we can see how the subject, an egg in this case, changes appearance with the
background within a few centimetres, then metres.
Then we test how it looks across different habitat types so we can see how well-tuned
the egg camouflage is in various environments.
We're able to model all sorts of different visual properties in the images – things
like colour, brightness and contrast differences, and the amount of edge disruption.
This example shows how we measure pattern differences – here's a crowned plover egg
where we filter out all but the very fine details, then we progressively look at the
larger and larger details.
The black and blue regions show where the egg has strong patterns at each scale.
We can then see whether the background has patterns at a similar scale.
At this point we attempt to answer the key questions about what makes good camouflage;
whether the crucial feature of the egg's camouflage is its colour, its pattern, it brightness,
or to what extent its outline is disrupted by strong markings like these.
We can also test whether the birds specifically choose nesting sites with a background that
makes their eggs look as camouflaged as possible.
We can also learn a lot by comparing the strategies of different species.
The fiery-necked nightjar you can see here lays its eggs under canopy of trees under
dappled light.
In contrast the Mozambique nightjar lays its eggs in open areas of burnt grassland.
Comparisons between species like these allow us to ask how specialised camouflage is to
different habitat types.
Plovers and coursers are easier to spot as they run away from their nests – here’s
a couple of crowned plovers foraging on a hot day, and this one enjoying a more mellow
dip.
This wattled plover is dive-bombing a water monitor lizard that got too close to its eggs.
Then there’s the Temminck’s courser, which runs so fast that it’s hard to keep up with
the camera.
And the bronze-wing courser whose chicks look very like burnt clumps of grass.
It's a nightmare when the GPS says you're within a couple of metres of the chicks, but
you just can't see them amongst all the other clumps of burnt grass.
Overall we sampled more than 250 nests in total across Zambia and South Africa, with
about 12 different target species and we took about 16,000 pictures in total.
The nests in Zambia were all found by a team of Zambian nest-finding assistants who are
brilliant field ornithologists, and have worked with my colleague Claire Spottiswoode for
many years helping with a variety of research projects.
They're amazingly good spotters and eventually manage to outwit the nightjars' camouflage.
We pay them for each nest they find, which supplements their livelihoods as farm labourers.
A world away from the baking heat of the Zambian dry season, here on the west coast of South
Africa, is the charismatic Kittlitz’ plover.
You can see here that it does a little dance on the nest to cover up its eggs with material
collected around the nest.
It’s the only one of our study species to this and very interesting because there’s
a trade-off between just leaving the eggs uncovered, or performing this dance, which
is fairly conspicuous once you get your eye in.
In South Africa there is also the chestnut-banded plover, which are quite rare and camouflaged
in grey on a windy beach here, and the blacksmith plover.
Our cameras showed blacksmith plovers destroying the nests of any kittlitz's plovers too close
to their own.
So the kittliz's camouflage needs to work not only against predators, but also bullying
competitors which we saw on quite a few nests.
In South Africa many of our plover eggs were taken by the pied crows as you can see here.
Their numbers are increasing rapidly as they expand further south, perhaps because of increased
urbanisation, and their growing numbers had a drastic effect on our focal species.
Of 36 kittlitz's plover nests we found, only two survived to hatching and we suspected
that the pied crows were a major source of predation… along with water mongoose and
the five-toed otter.
In South Africa there is also the white-fronted plover that lays its eggs on the beach, which
is terrifying because the beach is made of mussel shells, so it sounds like you’re
crushing eggs wherever you go.
However, you can see there are other dangers to laying your eggs on the beach.
Overall, we found from our hidden cameras that predation events are very, very rare.
This, along with the complex modelling, was one of the reasons why this was such a difficult
project that has never been done before.
And of course, the cameras ended up being attacked and disturbed on numerous occasions
– that’s just part of filming in the field where you can’t control all of the variables
like you can back in the lab.
Like all fieldwork, ours could be frustrating at times.
There were times when we couldn't find any new nests.
Or when it clouded over for days so we couldn't take photos.
Then there were potential dangers too – walking across baking hot ground in the sun and returning
to a piping hot car, often above 45 degrees centigrade, then there were the dangerous
and alarming roads, bush fires, insects – like this south African swarm…
And of course there were the snakes.
I nearly picked up this beautiful but venomous boomslang as I cleared a fallen branch from
the road.
There are also plenty aggressive and deadly black mambas in the area, but thankfully we
didn't encounter any of those.
But overall the field work went surprisingly smoothly.
We saw some brilliant sunrises getting up early to do the field work, and we documented
some amazing examples of camouflage while we were in Africa.
Like these insects, or this praying mantis devouring a meal.
Thankfully many of our nests did survive to hatching, and we sometimes even caught them
in the act – like these three-banded plover chicks that can stand and run just a few hours
after hatching, a little unsteadily at first though.
We also photographed chicks when we could, to see how the optimal camouflage strategy
might change through different life stages; we use the weight at time of photography to
judge the chick's developmental stage.
Back in the lab in Cornwall we're still processing the images – each photo takes a few hours
to prepare and process.
Some preliminary data show that plovers and coursers might be able to select patches of
ground to nest on that match the patterning of their eggs, and that there appears to be
a trade-off in egg colour between concealing your eggs to avian predators like the bush-shrike
you can see here, and concealing them from mammalian hunters.
We’re analysing the data now to find out the mechanisms behind this, but for now it
seems you can't fool everyone all of the time.