LIFE SIGHT
This complex is, to the best of my knowledge, unique in the zoo world. Rather than focusing on a geographical area or taxonomic grouping, it explores the incredible diversity of eyesight in the animal world.
The display is a single-story building which is long but not particularly wide, as it occupies the boundary between two existing areas of the zoo. The outside of the building is decorated with cutouts depicting several different animal eyes (with different eye colours, pupil shapes etc.) and the ‘g’ in the exhibit’s title, positioned on the end wall of the building above the entrance, is made up to look like a chameleon. The entrance area also has a garden filled with colourful flowers, in order to provide a treat to the eyes of visitors.
A major aim for creating this building is to provide a large, comfortable viewing area for seeing the zoo’s current
cheetahs (
Acinonyx jubatus) – an outdoor viewing area, not visible from the Life Sight gallery, is within a more traditional African section of the zoo. The enclosure will keep its current design that incorporates a large paddock with a mixture of short grass with longer grass and native wildflowers, a fallen tree for the animals to climb and bask on, some native shrubs to provide hiding places and a small drinking pool. Next to the viewing window will be an artificial rocky overhang to create a shady place for the cheetahs to relax on hot days while for cooler days there will be a solar-powered heated rock. These features will improve the enclosure for the cheetahs, providing comfortable conditions year-round and enhancing the visitor experience.
Upon entering the building, the first thing visitors see is the viewing window into the outdoor enclosure on the right. As with all the exhibits in this building, the species identification signage is put on the side of the window that visitors are expected to encounter first. This signage includes the species name, geographical distribution, diet, Red List status and wild threats. Otherwise, the rest of the signage around each animal is about how it sees the world. The signage around the cheetah exhibit talks about how the eyes of this cat have cells packed into a horizontal line, which allow it to scan the horizon for prey. They also have a 210-degree field of view compared to a human’s 140 degrees. A piece of equipment allows visitors to look through a headset that shows how cheetahs see. There is also signage about the black markings around their eyes which reduce glare from the sun, which is compared to the eyeliner used by the ancient Egyptians for the exact same purpose. It is thought that cheetahs have better colour vision than lions or leopards, as they hunt during the day and have a greater number of cone photoreceptors called S-cones that help distinguish colours. Finally, an animation shows how the cheetah receives information from its inner ear while sprinting, so that it is able to keep its head stable and its eyes locked on its prey.
After seeing the cheetahs, visitors begin to explore the building proper. To make each artefact, the information and the enclosures stand out, the walls and plinths that smaller terrariums are set upon will all be white. There is science behind this decision, as white reflects all wavelengths of the visible spectrum and so the iris does not need to widen to absorb more light. The first display after the cheetahs is a simpler one, showing the properties of light. A simple experiment allows visitors to, via the press of a button, shoot a light beam through a prism to display the visible spectrum. Then come a set of four bronze animal heads, showing how the different placements of the eyes can show how an animal lives – the cheetah has eyes on the front of its head because it scans in front of it to locate prey, the gazelle has eyes on the side of its head to cover a wider view and spot approaching predators while the crocodile has eyes on top of its head so it can see prey without exposing too much of its body.
On the left-hand wall is a series of displays looking at the evolution of the eye. A large cutout image of a Planarian shows creatures probably quite similar to those who developed sight – their eyes are little more than simple receptors that can tell light from dark. Next along the wall is a series of casts showing an uncurling trilobite, probably the first animals to have complex eyes. These invertebrates have compound eyes with many lenses, made of hard calcite that helped with image clarity. The next fossil is a cast of a 300-million-year-old fish,
Acanthodes bridgei, which provides the first evidence of colour vision from any animal – the retinas of this fish have cone cells, which are colour sensitive. The end of this wall has a small marine aquarium for a live species, a small group of
maxima clams (
Tridacna maxima). The tank is fairly simple, with pale sand, a large piece of coral rock in the middle of the tank for the clams to attach to and bright overhead lighting to allow the photosynthetic organisms inside the clam to flourish.
Next to the clam tank is information about how they view the world. Giant clams have several hundred small pinhole eyes at the edge of the fleshy mantle. Pinhole eyes are the shape of a deep cup with a narrow opening, but lack any sort of lens. Although giant clams are sensitive to three different colours, their simple eyes are unable to combine the information. This means they see colourful but otherwise undefined images. However, they are able to detect nearby movement, which allows the clam to defend itself by either spraying out a jet of water to startle predators or by slamming its shell closed. A computer screen by the clam tank shows a scene as a human would see it and, by pressing a button underneath, the scene changes to how a giant clam would view it.
In the middle of the floor in this first section there is a free-standing paludarium. Inside the paludarium is a raised island made to look like muddy ground that is surrounded by fairly deep water, with a substrate of brown river sand and planted with native aquatic plants such as hornwort and water crowfoot. The island is planted with wetland emergent plants such as yellow flag and greater pond sedge. This will provide open flying space, perching areas and breeding habitat for the inhabitants, a group of
azure damselflies (
Coenagrion puella). This brilliantly-coloured native species has been bred in captivity before. The access door for keepers is close to the water’s surface, as it can be expected that most of the damselfly’s flights will be above this height. To feed them, a pot of fruit flies will be floated on the surface of the water and left until the pot is empty.
The signage around this display looks at the vision of dragon and damselflies. They have two enormous compound eyes with up to thirty thousand lenses, more than any other animal. The spherical nature of the eye and the many lenses allow these insects to look in all directions simultaneously and so look out for prey, predators and rivals. However, the number of lenses does mean that the image comes through as a mosaic, rather than the clear images we are used to – a headset allows visitors to see in this way. As well as the two larger eyes, these insects have three much smaller eyes to help with navigation. Additionally, they have amazing colour vision – while humans have trichromatic vision, meaning that our colour vision is based entirely off a combination of red, blue and green wavelengths of light, dragonflies see no fewer than eleven different wavelengths and some see as many as thirty. It may be that this incredible colour vision allows the ultraviolet spectrum to be fully visible, allowing the dragonfly to stabilise itself in flight. Obviously, this is impossible to represent in visual media, so instead an approximation with visible colours will be used.
Visitors round the wall on which the clam and dragonfly vision signage is located on and pass an image and information about the vision of mantis shrimps. These invertebrates have some of the most sophisticated vision in the animal kingdom, with independently moving compound eyes that have between twelve and sixteen visual pigments depending on the species – not as many as some dragonflies, but still impressive. They are also the only animals known to be able to see circular polarised light, which they may use to communicate warnings to others of their species.
Entering the next ‘sub-room’ within the building, visitors are first directed towards one of the three larger enclosures built on the opposite side of the building to the cheetah enclosure, for housing slightly larger species that require or appreciate access to outdoor areas seasonally. This enclosure is primarily a conservatory-type building that can, when the climate is suitable, be opened to a PVC-screened outdoor aviary with a pair of horizontal sliding doors. This is an ideal enclosure for
Parson’s chameleon (
Calumma parsonii), which are a fairly cold-tolerant species of chameleon that flourishes when given outdoor access in such temperate places as Germany and Minnesota. Both the enclosures are densely planted with chameleon-safe plants, with a mixture of dead branches and living smaller trees to provide amble vertical climbing, as well as artificial vines to provide horizontal climbing opportunities. When the conservatory is opened to the outdoor aviary, an artificial vine is manually put up to connect a tree in the indoor area to one outside. A second and smaller off-show screen enclosure will house the second of the pair of these lizards.
Chameleon eyes are one of their most recognisable features. The eyes are on turrets that can be moved independently of each other and give it almost 360-degree vision. This allows them to switch between monocular vision, when each eye is used to look at a different image, and binocular vision, when both eyes look at the same scene. They use monocular vision to scan for both predators and prey, switching to binocular vision when prey has been spotted and they are judging the angles needed to fire out their long tongue. An animation on a screen shows the switching between monocular and binocular vision, demonstrating how chameleon vision works. Also, the role of the chameleon’s eye in culture is explored on a nearby sign. Perhaps it was their alien-looking eyes that led to the Tunisian tradition practice of burying a slaughtered chameleon in the foundations of a house to protect against the evil eye?
The next display is another elevated plinth, this one fully aquatic with deeper water and a much smaller central land area that supports an artificial mangrove tree, with roots that extend out into the water. This is home to a sure-fire inclusion for any exhibit about animal eyesight, a shoal of
largescale four-eyed fish (
Anableps anableps), a large species of livebearer from the coast of northern South America that can be readily bred in aquarium conditions. This tank is much larger than the damselfly one, in order to house a sizeable shoal of these social fish. The substrate is a layer of fine sand, with a couple of flat rocks coming to just below the surface, as young fish like to bask on these. A bright overhead light encourages algal growth on the roots to provide grazing opportunities but otherwise there are no aquatic plants, which do not regularly grow in the mangrove swamps these fish normally inhabit.
The strange thing about this fish’s eyes is that the pupils are seemingly split in half horizontally, allowing them to look both above and below the water simultaneously. Each half-eye has its own pupil and retina which allow them to operate independently of each other. A headset allows visitors to see the split-screen view that four-eyed fish have. A unique problem this species faces for a fish is that it lives in a sunny tropical environment with its eyeballs exposed; the fish has evolved a defence, with the upper half of the eye being thicker and enriched with glycogen to protect it against drying and from UV exposure. The mystery behind the function of these eyes is also explored – it has long been considered that this strange setup is purely for detecting predators, but it may actually be for helping with feeding. The lower eyes look for algae and other submerged food, while the upper eyes can be used to detect prey such as small crabs on mangrove stilt roots as well as watching the state of the tides, so allowing the fish to exploit a very narrow ecological niche.
As visitors leave behind the chameleons and fish and round the corner towards the third ‘sub-room’, they pass a large paludarium set into the wall on the cheetah enclosure side of the building. There is a large pool of slightly brackish water in this display, with dark river sand as the substrate and no other aquatic vegetation. About a fifth of the exhibit is land, planted with several parlour palms and featuring a combination of a large artificial mangrove tree (with roots extending out into the water) and small live mangrove saplings. This is the only mixed-species exhibit in the entire complex, housing a small shoal of
banded archerfish (
Toxotes jaculatrix) in the water and a
Burmese vine snake (
Ahaetulla fronticincta) crawling through the vegetation. Both are native to the mangrove forests of Southeast Asia and both species have been successfully mixed at the California Academy of Sciences. The main breeding group of vine snakes live off-display. A small pool on the land section allows the snake to be fed easily – attempts will be made to try and wean it onto dead rather than live fish. The archerfish will be fed by scattering insects into the plants. Access is on the right-side of the paludarium where the land section is, while the filtration is stored to the left of the tank the tank.
The archerfish and vine snake both represent the same problem with vision, one of seeing prey through the refraction of the water’s surface – the fish needs good vision to snipe insects off overhanging vegetation while the snake needs to capture small fish from the water without missing. Archerfish have vision as acute as a human and this, coupled with their surprising intelligence for a fish, make them very successful hunters. Much less research has been done on how Burmese vine snakes hunt, but the hope is that our captive colony may be able to be used for studies into this. On the wall to the left of the paludarium is information about another predator that has to contend with surface glare, the common kingfisher. To stop glare from interfering with its hunting, kingfishers have droplets of special oil in their eyes which act like built-in sunglasses. This can be represented by a picture of a sunlit water surface that, when a button underneath is pressed, shows the kingfisher’s eye view of fish hiding under the surface once the glare is removed.
Visitors then continue on, to look out into the second larger outdoor enclosure. This one is an entirely netted aviary with a small nesting box disguised within a dead tree to provide the indoor area. This exhibit is themed on a savannah bushland, with a substrate of dirt and sand, small clumps of tall grass on the ground, some wildflowers such as lavender to attract insects and a couple of trees, both dead and living, with some horizontal branches nailed to them to provide additional perches. This is for a pair of
little owls (
Athene noctua), a species with eyesight typical for an owl. Although other species of owl are recommended for keeping instead of this one, the little owl has the advantage of being partially diurnal – the more nocturnal owls are likely to spend a lot of time with their eyes closed, so preventing visitors from seeing the feature for which owls are included in this display.
There is a lot to talk about regarding the vision of owls, as their eyes are among their most notable features. They have an abundance of rod cells in their eyes which gives them amazing vision under low light levels, but this comes at a cost of them not having good colour vision. Graphics showing the difference and importance of rod and cone cells is included here. More information is included specifically about owl eyes and how they have had to adapt their whole bodies around their vision. A pair of models compare a rounded human eyeball with the tubular eyeball of an owl. To hold these eyeballs in place, the owl has had to evolve bony sclerotic rings but this means that the owl cannot move its eyes inside its skull. Instead, it has to twist its neck in order to turn its head and look at something new – a 3D model allows visitors, via a button press, to see how the skeleton and muscles of an owl’s neck allow it to perform such a feat.
The next display is not about an animal housed in the collection, as doing so is not possible and housing its relatives is probably not practical. The eyes of squid are well-adapted to seeing in the dark midwater levels of the ocean. Most animals with a spherical lens have to trade-off between the speed of gathering light and image crispness, but squid are able get crisp images through such a lens by moving the proteins in the lens, so that the densest ones are in the centre and less dense proteins are at the edge. As well as this unique setup, squids possess the largest eyes in the animal kingdom – a model of a colossal squid is included, with emphasis drawn to its football-sized eyeball. Their huge eyes also have photophores at the rear of the eyeball, where a chemical reaction involving bacteria creates light sufficient for the squid to see its prey in the dark. Also on this display wall is a life-size cutout of a cock-eyed squid, which has eyes of dramatically different sizes – a small blue eye that scans the depths for predators and a large, bulging yellow eye to detect prey swimming above.
On the right-hand wall, after seeing the colossal squid, visitors encounter a wall-mounted horizontal terrarium with tinted glass that darkens the interior. The tank is lined with sand and has a rocky backing, as well as scattered limestone rubble and a small scorched branch to add to the feeling of being in a desert landscape. This enclosure is home to a breeding pair of
helmethead geckos (
Tarentola chazaliae), listed as Vulnerable on the IUCN Red List. Any eggs produced by the pair are moved off-show to be hatched and reared. Dimming the enclosure allows these nocturnal geckos to be viewed active during visitor hours.
Geckos have a diversity of different eyes but one feature shared by many of them is a lack of eyelids. This may help it hide from both predators and prey, where even the minor movements of a blinking eye could give them away. As part of their defence mechanism, many geckos also have eyes that match their surroundings and so act as camouflage. But being unable to blink does leave the eye vulnerable to dirt, so geckos lick their eyeballs to clean them. A feature known to the helmethead gecko specifically is that they are able to see colour very clearly in dim light – their eyes are up to 350 times more sensitive to colour at night than those of a human. A headset near the gecko tank compares the night vision of a helmethead gecko against that of a human.
Along the walkway between the geckos and the final ‘sub-room’, there is more information about animals that have remarkable vision in the dark. First is a massively magnified cutout of the ostracod
Gigantocypris, which has concave eye mirrors instead of lenses. They are thought to have the best night vision of any animal, and use their keen eyesight to spot the bioluminescence of the small invertebrates they prey upon. Perhaps even odder is the annual change that happens in a much more familiar animal, the reindeer. During summer, the tapetum within their eyeball is golden but come winter it changes colour and turns blue. It is thought that this helps the animal to make the most of the drastically changing light conditions that come in the arctic.
The third and final one of the outdoor enclosures viewed on the left-hand side of the building is the largest and also the only one with an off-show indoor area. The outdoor enclosure is themed on a rainforest, with deep leaf litter, fallen logs and ferns on the ground, live small trees and bushes, partial tree trunks and artificial vines connecting many of these. Close to the viewing window, a canopy above the aviary netting provides a shaded area and a mister is also included to be used intermittently both for watering the plants and cooling the animals on warmer days. The inhabitants of this enclosure are a breeding troop of
red-bellied tamarins (
Saguinus labiatus), a sociable small primate from the rainforests of the Amazon Basin. The off-show indoor area is much more basic and less naturalistic and primarily serves as a resting place, a secure retreat area and also contains a separation enclosure for veterinary or animal movement purposes.
Callitrichids, the family that includes tamarins and marmosets, have vision unique among mammals – a much higher than average proportion of individuals have some degree of colour blindness. In some species, all the males and some of the females are unable to distinguish red and green. In some cases, a troop of tamarins may have individuals that see colours in six different ways. This may offer some advantages – individuals within the group are not competing for food. The colour-blind monkeys, while maybe not as efficient at picking out ripe fruit, are not distracted by colour when hunting insects and instead see patterns. This helps them to more easily detect camouflaged prey and may also help spot predators. To show this, two boards by the visitor area show a colour and partially-coloured image to demonstrate how picking out a hiding insect is easier. There is also information about human colour blindness, which affects around 1 in 12 men and 1 in 200 women.
The tamarins are the beginning of the final ‘sub-room’. On the wall behind the low-light animal vision information (
Gigantocypris, reindeer) is information about the vision of tarsiers, which have the largest eyes compared to body size of any primate. A wall-mounted mirror with a pair of false eyes show visitors just how large human eyes would need to be to be as large as those of a tarsier – as big as a grapefruit. These huge eyes help it to hunt in the dark.
Positioned along the right-hand wall of this room are a series of three terraria, all housing different species of frog and toad. The first is a large, horizontally-orientated enclosure with a deep soil layer, a couple of dead logs and plantings of live moss. This is home to a group of
tomato frogs (
Dyscophus antongilii) which are native to Madagascar. The second is a vertically-orientated space with a live shrub with climbing passionvines twining among their branches. There are also bromeliads and air plants stuck to the branches and even on the side glass. This is home to a breeding group of
red-eyed tree frogs (
Agalychnis callidryas), a highly recognisable species from Central America. The third and final tank is another horizontal one, although this is more of a paludarium, with a shallow water area at the front filled with duckweed and with curly sedges at the water’s edge. Otherwise, the bank is again covered with logs, dead leaves and moss like the tomato frog tank and is home to
yellow-bellied toads (
Bombina variegata), natives of Central Europe.
The nearby signage primarily shows the incredible diversity of frog and toad eyes – although 78% of studied species have pupils with horizontal slits, there are many other shapes. The red-eyed tree frog has vertical slits, the tomato frog has rounded pupils and the yellow-bellied toad, quite uniquely, has heart-shaped pupils. Other shapes include diamonds, triangles and fans. At the moment, it is a mystery what this diversity serves – there seems to be no relation between pupil shape and the time of day a frog or toad is active at. In general, amphibians see well in colour but are particularly driven by movement. If an insect doesn’t move, the frog will not eat it but as soon as it starts moving it will be detected from a considerable distance.
The final enclosure in this building is a free-standing aquarium. The substrate is sand, with a pillar of replica sandstone in the middle rising above the water surface. In the water there are a few water plants as well as sandstone pebbles on the bottom to provide perching places for the inhabitants, a large group of
sunburst diving beetles (
Thermonectus marmoratus). These insects are colourful, active and can be easily kept in large groups, so provide an excellent exhibit. Off-show facilities have an additional backup colony where most of the breeding takes place; the on-show group is mainly for display.
These beetles have recently come to prominence in the scientific world for their amazing vision. The larvae have a total of twelve eyes but between them have twenty-eight retinas. This means that each eye is bifocal, like the different lenses of a camera. These bifocal lenses can even be asymmetrical, which enhances the resolution of the beetle’s vision. The eyes are not attached to any muscles which means the larva cannot move them and so instead has to scan by moving its head, much like the owls the visitors encountered earlier. The six pairs of eyes are on top of the head but to fill in the gap in vision on top of the head, the larvae also have an eye patch, which has retinal tissue but no lens – it cannot detect images but can tell the difference between light and dark, alerting the larva to a predator swimming overhead. When they pupate into adults, the larvae have more basic compound eyes. A set of asymmetrical bifocal spectacles on the nearby wall allow visitors to look at different things in different resolutions simultaneously, just as the beetle larva does.
Along the left-hand wall, between the tamarins and the exit to the building, is information about how the vision of animals can affect us. The main example looked at is the sloth bear, considered to be among the most aggressive of the bears and responsible for hundreds of deaths. This apparent aggression may be entirely due to the animal’s vision. The sloth bear’s problem can be illustrated with a simple game on a screen – the picture is blurred so the animals moving through the vegetation are mainly obscured. A red and green button allow the player to either attack the unseen animal or let them pass. The issue is that each movement in the vegetation could be a predatory tiger or leopard, but the bear is unable to sense this. So, the bear is forced to respond to these unknown threats with maximum violence, as if its life were in danger. This shows visitors how the vision of animals can dramatically alter their behaviour.
Having seen all these remarkable creatures and learned how they see the world visitors exit the building on the left-hand side and move back into the rest of the park.
Just along the path from the main Life Sight building is the Life Sight classroom, where school groups can be taken to learn more about animal vision. This will involve meeting animal ambassadors (all common species suited for public handling such as barn owl, cane toad, bearded dragon, domestic rabbit and pygmy goat) and also using a VR headset with a free tool called Tarsier Goggles
TM, which allows the wearer to experience a simulated environment in the way a tarsier does.
An off-show area is included within the design near the start of the building, on the left-hand side and before the chameleon enclosure. In here will live the main breeding group of vine snakes, the second adult chameleon, rearing facilities for young geckos, chameleons, four-eyed fish and amphibians, as well as backup colonies for the damselflies and diving beetles. The cheetahs will remain under the care of the Carnivore team, the owls and tamarins will end up under the care of the Bird and Primate care teams respectively and the other animals will all be cared for by the Lower Vertebrates and Invertebrates care team – the off-show room is designated to the latter team. Food for the animals in this exhibit will be bred and managed in the nearby zoo kitchen that is separate from any display animal buildings, to prevent potential disease overspill or infestation from livefood invertebrates.
A lot of the information about animal vision came from this link (which partially helped inspire the exhibit):
Amazing eyes: 17 vision champions
The images with a sliding scale showcasing differences in animal and human vision would be like the ones on this link:
How do other animals see the world?
A scientific paper about the creation and application of the Tarsier Goggles can be found here:
Tarsier Goggles: a virtual reality tool for experiencing the optics of a dark-adapted primate visual system | Evolution: Education and Outreach | Full Text
