Bald Eagle Eyesight
The eyesight of a Bald Eagle is impressive. Part of the reason for their excellent vision is that these birds of prey have two centers of focus (foveae), which allow them to see both forward and to the side at the same time. Cone cells, one of three types of photoreceptor cells in the retina, perceive color, fine detail and rapid movement. In a human, the fovea has 200,000 cones per millimeter; in the central fovea of a Bald Eagle’s eye, there are about a million cones per millimeter. An eagle’s eye is almost as large as a human’s, but its sharpness is at least four times that of a person with perfect vision.
Bald eagles are capable of seeing fish in the water from several hundred feet above, while soaring, gliding or in flapping flight. (They locate and catch dead fish much more rapidly and efficiently than live fish, because dead fish float with their light underside up, making them easier to see.) It is very likely that a Bald Eagle can identify a rabbit moving almost a mile away. This would mean that an eagle flying at an altitude of 1000 feet over open country could spot prey over an area of almost 3 square miles from a fixed position. (photo: recently fledged, juvenile Bald Eagle)
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Shrew Eyes
Shrews have a very high metabolism and spend most of the day and night hunting for food. Subterranean worms and insects are their main prey, which means that a lot of their time is spent in tunnels, where there is little, if any, light. Consequently, shrews have little need for large eyes or excellent vision, neither of which they have.
While the sight of most shrews is probably limited to the detection of light, some species compensate by using other senses, including hearing and touch, to direct them. The Short-tailed Shrew has a well-developed repertoire of squeaks and clicks, including ultrasonic sounds, for navigation and predation. (photo: hair has been brushed aside in order to see eye slit)
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ANIMAL MOUTHS: Second Book in Children’s Series Released
Some of you may have seen Animal Eyes, which was the first of a series of children’s books I am writing about animal anatomy. Just as Animal Eyes took a look at the adaptive differences among different animals’ eyes, Animal Mouths describes the wide range of animal mouths. From birds to butterflies, different mouths and mouth parts are illustrated with photographs and their adaptations for different diets are discussed. Carnivores, herbivores and omnivores are included, as well as an educational section at the end of the book which provides children with photographic/textual “mix and match” activities that reinforce information presented in the main text. Available from the publisher (click on cover image to the right), independent bookstores (most will order if it’s not in stock), online and from me (from those of you nearby). This fall the third book of this series, Animal Feet, will be released.
Owls & Humans Share Trait
Birds have three eyelids – an upper eyelid, lower eyelid and a third semitransparent membrane called a nictitating membrane that sweeps across the eye much like a windshield wiper. This membrane keeps their eyes moist, and protects their corneas from being scratched.
In most birds, including owls, the upper and lower eyelids are used to close the eyes when sleeping, and the nictitating membrane is used for blinking. Humans close their eyes mainly by lowering the upper eyelid, where most birds do so by raising the lower lid. Owls (and a few other birds such as parrots, toucans, wrens and ostriches) are more human-like in that their upper lids are usually lowered to close their eyes. Owls also usually close their eyes, partly or entirely, when capturing and transferring prey, scratching their face, preening another owl and copulating. (Note the rows of feathers on this barred owl’s upper eyelids.)
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Newest Children’s Book Release
Animal Eyes is the first of a series of early childhood books on animal parts which I am currently writing (mouths, tails, feet, etc. to follow). This book takes a look at the eyes of a variety of animals and explores what their size, number, color and position tells us about the life style of animals as far-ranging as owls, flying squirrels, spiders and dragonflies. Appropriate for ages 3-8. Accompanying the text for each animal is a two-page, close-up photograph. “Animal Vision Fun Facts,” a “Match the Eye to the Animal” activity and an illustrated Glossary provide additional educational information at the end of the book.
Turkey, anyone? How Red Fox Kits Entertain Themselves
This two-month-old Red Fox kit (blue eyes turn brown after the age of two months) amused itself for several minutes with this Wild Turkey tail feather – tossing it up in the air, pouncing on it, chewing it and just carrying it around to impress/taunt its litter mates. Kits are old enough to spend much of their day above ground now and their antics are entertaining, to say the least. While parents are off during the day hunting and/or getting a rest from rambunctious offspring, said offspring amuse themselves by digging, scratching themselves, chasing each other, grooming themselves and chewing on any and everything, from sticks and leaves to the remains of past meals, such as feathers and bones.
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The Eyes of Common Goldeneyes
Common Goldeneyes, birds of the boreal forest, overwinter as far north as open water permits, which includes parts of northern New England most years. These birds get their common name from the color of their eyes, but their eyes don’t attain this golden color until their first winter. When they hatch, Common Goldeneye ducklings have gray-brown eyes. Their eyes turn purple-blue, then blue, then green-blue as the ducks age. By the time they are five months old, their eyes are pale green-yellow. They turn bright yellow in males and pale yellow to white in females by mid-winter.
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A New Book for Budding Naturalists
Is there a youngster in your life who might love his or her own book about beavers? My third children’s nature book, The Beavers’ Busy Year, has just been released. Having been an ardent admirer of this rodent for many, many years, it is gratifying to have had a chance to instill a love for beavers in youngsters age 3-8 with this non-fiction book. The adaptations of beavers’ noses, eyes, ears, fur, feet and tails are highlighted in the text and photographs take the reader through the seasons of the year from a beaver’s perspective. Activities at the end of the book engage children in matching photographs of various beaver signs such as tracks, scent mounds and incisor marks with written descriptions. There are also activity/informational sections on beaver tails, beavers as engineers and creators of habitat for other wildlife, and dam building. It should be available at your local bookstore, but if not, I’d greatly appreciate your letting them know about it. Thank you!
Nictitating Membranes
If you look closely, you’ll see that part of this American Crow’s eye appears white. This white (actually transparent) part of the eye is referred to as a “third eyelid,” or nictitating membrane. Many animals, including some fish, mammals, reptiles, amphibians and birds, have nictitating membranes. Instead of moving up or down like the upper and lower eyelids, they move horizontally across the eye, much like windshield wipers. These membranes lie under a bird’s eyelids. When not in use, they are curled up in the inner corners of a bird’s eyes, but can be quickly drawn across the eyes to protect, clean and moisten them without shutting out the light.
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What a Snake’s Eyes Can Tell You
You can tell a lot about a snake just by looking at its eyes. Snakes that burrow underground usually have relatively small eyes compared to those that live above ground. The size of the eye and the shape of the pupil can often tell you if the snake is diurnal or nocturnal – typically diurnal snakes have comparatively small eyes with round pupils and nocturnal snakes have larger eyes with elliptical pupils. Both of these characteristics have to do with maximizing or minimizing the amount of light that enters the eyes. The larger the eye, the more light it can gather. The reason for the difference in pupil shape is that round pupils can close very tightly, to a pinpoint opening, shutting out bright sunlight very effectively. Elliptical pupils can open wider than round pupils, and consequently collect more light. (Photo is of a Common Gartersnake.)
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Moth Eyes and Biomimicry
Because moths need to use every little bit of light available in order to see in the dark, their eyes are highly non-reflective. (This is also helpful in decreasing the chances of predators spotting them.) Scientists, through biomimicry, have come up with a number of technological advances, including the development of a film that can be applied to solar cells which helps keep sunlight from being reflected off of them before the light can be utilized. Man-made materials based on the structure of moth eyes could someday reduce the radiation dosages received by patients getting x-rayed, while improving the resolution of the resulting images. Research on recreating the pattern found on moths’ eyes onto plastic could lead to reflection and glare-free display screens for televisions, cell phones, computer monitors, eyeglasses, speedometers and more.
Turtle Eyes
When a turtle moves its head, its eye moves to compensate, so that its eye remains in the same position – parallel to the horizon or pond surface — no matter what position the turtle’s head is in. This type of eye stabilization is called vestibulo-ocular reflex (VOR). Humans have a very similar reflex, but it’s easier to detect on a Painted Turtle (pictured) because of its dark eye line. A turtle’s eye structure is stabilized to the horizon, which makes sense, as turtles spend their life close to the ground and/or the pond surface, and this reflex enables it to align its vision horizontally in order to find food, a mate and predators.
New Children’s Book by Mary Holland
Do you know a 3 – 8 year old who loves animals and would enjoy getting close-up views of the antics of a red fox kit during the first summer of his life? My second children’s book, Ferdinand Fox’s First Summer, has just been published by Sylvan Dell in both hardback and paperback. I have been lucky enough to have had the opportunity to observe and photograph young red foxes as they interact with each other and with their parents. This book consists of a selection of these photographs, accompanied by text and an educational component at the end of the book. Look for Ferdinand Fox’s First Summer in your local bookstore. If they don’t carry it, you would be doing me a huge favor by asking them to. Thank you so much. My next children’s book is on Beavers and will be coming out in the spring of 2014. (I am still looking for a publisher for Naturally Curious Kids!)
A Great Christmas Present!
If you’re looking for a present for someone that will be used year round, year after year, Naturally Curious may just fit the bill. A relative, a friend, your child’s school teacher – it’s the gift that keeps on giving to both young and old!
One reader wrote, “This is a unique book as far as I know. I have several naturalists’ books covering Vermont and the Northeast, and have seen nothing of this breadth, covered to this depth. So much interesting information about birds, amphibians, mammals, insects, plants. This would be useful to those in the mid-Atlantic, New York, and even wider geographic regions. The author gives a month-by-month look at what’s going on in the natural world, and so much of the information would simply be moved forward or back a month in other regions, but would still be relevant because of the wide overlap of species. Very readable. Couldn’t put it down. I consider myself pretty knowledgeable about the natural world, but there was much that was new to me in this book. I would have loved to have this to use as a text when I was teaching. Suitable for a wide range of ages.”
In a recent email to me a parent wrote, “Naturally Curious is our five year old’s unqualified f-a-v-o-r-I-t-e book. He spends hours regularly returning to it to study it’s vivid pictures and have us read to him about all the different creatures. It is a ‘must have’ for any family with children living in New England…or for anyone that simply shares a love of the outdoors.”
I am a firm believer in fostering a love of nature in young children – the younger the better — but I admit that when I wrote Naturally Curious, I was writing it with adults in mind. It delights me no end to know that children don’t even need a grown-up middleman to enjoy it!
Jumping Spiders
Jumping spiders are aptly named as they can spring more than 50 times their own body length to land on unsuspecting prey. They hunt actively rather than catching prey in a web and they have excellent vision, with four big eyes in front and four smaller eyes on the top of their head. Jumping spiders have three-dimensional vision which allows them to estimate the range, direction and nature of potential prey, essential skills for a predator that catches prey by pouncing on it.
Snake Eyes
You can often tell whether a snake is active in the day (diurnal) or during the night (nocturnal) by looking at its eyes. Diurnal snakes, such as the pictured Common Gartersnake, typically have round pupils and moderate-sized eyes. Many nocturnal snakes have large eyes and many also have vertical, elliptical pupils. A round pupil is able to close tightly to a pinpoint opening, allowing a minimum amount of light to enter the eye on very bright days. In contrast, a vertical pupil can open wider than a round pupil to allow more light to enter the eye, a useful adaptation for night vision.
Naturally Curious with Mary Holland 
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