Not all eggs are the same. When we think of eggs what usually comes to mind is a perfectly oval shaped white egg safely packed in a carton. Most of us don't think of the myriad other types of eggs that exist in the animal world. In fact, most animals on our planet lay eggs instead of having live birth. These eggs can be very varied though. Some eggs are slimy, some are leathery. Some eggs are laid in nests, while others are neatly connected in strands, or glued together using foam. This lens will highlight some of the 'less thought of' varieties of eggs.
Bird Eggs
the classic egg
Most of us are familiar with the standard bird egg. Bird eggs come in a wide range of sizes and colors. What sets bird eggs apart from most other eggs is their hard outer shell. The award for the largest egg produced by a living species of bird belongs to the ostrich. Ostriches can produce an egg that is 6 inches long and weighs 3 pounds! The smallest bird egg is laid by the bee hummingbird.
Reptile eggs
Scaly egg-layers
Reptiles lay eggs just like birds. Their eggs look and
feel a little different though. Instead of having a hard
and 'crunchy' outer shell, reptile eggs feel leathery.
Lizard and snake eggs tend to be especially soft,
while the eggs of tortoises, turtles, and crocodilians
are harder. All of them, however, are softer than bird
eggs. Reptiles fertilize their eggs internally as do birds.
Reptiles include animals such as alligators, crocs, snakes, lizards and turtles. Some reptiles appear to give live birth, but it's not quite as it seems. What's actually happening is that the egg is hatching inside the female and the young emerge alive. There is, however, no placental relationship between the young and their mother. The egg develops on its own inside of her.
Amphibian eggs
Slimy!
Amphibians also lay eggs. Amphibians include such animals as frogs, toads, salamanders, caecilians and newts. Their eggs lack the harder outer shells that characterize bird and reptile eggs. Instead, they are slimy and gel-like in texture. Since they have no hard outer layer, they are prone to water loss. For this reason, many amphibians lay their eggs directly in water. Some species of frog will lay their eggs outside of water but use a moist foam to keep the eggs from drying out. In frogs and toads, egg fertilization occurs externally. The amplexus or 'clasping' posture ensures that the male fertilizes as many eggs as possible. In most other amphibians, fertilization occurs internally. In frogs and toads, eggs are laid in what are sometimes very elaborately constructed strands or clumps. The larvae, or tadpole, hatches to begin its metamorphosis. There are many variations on this procedure among amphibians. Some amphibians retain their immature larval form, and some complete the metamorphosis inside the egg and hatch as miniature adults. Amphibians have some of the most fascinating eggs/reproductive strategies in the animal world. Egg-laying mammals
Can you name them? there are 2
Egg-laying is rare among mammals, but there are some that manage to do so. They are the echidna and the platypus. Echidnas can be found in Australia and New Guinea. There are 4 species alive today, and all lay eggs. Echidnas are spiny animals with an appetite for small insects. The eggs they lay are soft and leathery much like a reptile. An echidna's egg is deposited directly into her pouch where it remains until hatching 10 days later.
Apart from the 4 species of echidna, the platypus is the only other egg-laying mammal on our planet. It can be found in eastern Australia, including Tasmania. The platypus female will usually lay a clutch of ~2 eggs in a nest. She incubates them by clutching them between her tail and lower abdomen for 10 days. Just like the echidna, her eggs are leathery and soft, like reptile eggs.
Apart from the 4 species of echidna, the platypus is the only other egg-laying mammal on our planet. It can be found in eastern Australia, including Tasmania. The platypus female will usually lay a clutch of ~2 eggs in a nest. She incubates them by clutching them between her tail and lower abdomen for 10 days. Just like the echidna, her eggs are leathery and soft, like reptile eggs.
Fish eggs
Fish are another group of egg-laying animals. Fish have a number of egg-laying strategies. Some release eggs into open water, leaving them to either float or sink. Some fish (mostly freshwater) build crude nests and stand guard over their eggs, fanning water over them with their fins. Still others are mouth brooders, keeping eggs in their mouth. In this case, water flowing through their gills and mouth keeps a current flowing around the eggs, turning them as it flows. Not all fish are egg layers though. Some are ovoviviparous, where the eggs hatch inside the female's body and young are born live. Great white sharks are ovoviviparous. Still others are similar to mammals in that they have a placental relationship with their young. Whale sharks and bull sharks are examples of this. These animals give birth to live young also.
Invertebrate eggs
Believe it or not, we've just scratched the surface of 'egg variety' on our planet. Most animals on our planet are invertebrates and a large number of these invertebrates are egg-layers. Yes I'm talking about insects, arachnids and the like. Check out the pictures below to see some of the variety among these egg-layers.
Biology Vocabulary
Egg related words
Here are some egg-related biology vocabulary words.
- viviparous - Definitions from Dictionary.com
- Do you know what this means? Humans are viviparous, as are dogs, elephants, and whale sharks. Guess, and check the definition to see if you're correct.
- ovoviviparous - Definitions from Dictionary.com
- Try this one. Here are some clues- boa constrictors are ovoviviparous, as are great white sharks and Jackson's chameleons.
- oviparous - Definitions from Dictionary.com
- Examples of oviparous animals iclude bald eagles, alligators, and ducks. Do you know what it means?
- monotreme - Definitions from Dictionary.com
- The echidna and the platypus are monotremes. Check the dictionary.com link for the exact definition.
Egg-hatching videos
Check out these neat videos of 'egg hatchings.'
Chick Hatching
Eagles Switch Places 9:17am Apr 28
Bearded Dragon Being Born
duckling
curated content from YouTube
Favorite Animal/Zoo Links
Here are some of my favorite animal and zoo-related links.
- Bergen County Zoo Docents
- Here at the Bergen County Zoo we have over 65 docents or volunteers. 'Docent' is a word meaning 'to teach' and that is exactly what our docents do.
- Horns or Antlers?
- Horns or antlers? What's the difference? Here's the scoop. There are indeed some differences.
- Bergen County Zoo docents blog
- Our blog. Docents- check here for daily updates/discussions about the zoo. Comment if you wish.
- American Zoo and Aquarium Association
- AZA has information on all accredited zoological parks. It also has great information on the positive things accredited zoos are doing to conserve wildlife.
- Animal Diversity Web
- A great resource for learning about animals from the University of Michigan.
- Association of Zoo and Aquarium Docents
- Learn all about docents. Virtually every zoo or aquarium has them. Find out more about the great work they do- maybe even look into becoming one!
- Bergen County Home Page
- Official site of Bergen County, New Jersey NJ. Information on our zoo is available on this site.
- Infrared Zoo Gallery
- See warm-blooded and cold-blooded animals in infrared light.
- American Birding Association
- If you enjoy birding as a hobby, check out this site.
- U.S. Fish and Wildlife Service Home
- Here's the US Fish and Wildlife page.
- NJDEP Division of Fish & Wildlife
- Homepage of the New Jersey Divison of Fish and Wildlife. Up-to-date information about hunting, fishing and NJ wildlife, management programs, stocking schedules, record fish, external links, news releases and news release archive, and more.
Animals in the news
Here's some animal related news from Discovery:
Fetching RSS feed... please stand byWildlife news
Here's some news on wildlife from google:
Fetching RSS feed... please stand byGreat Stuff on Amazon
Here are some books on egg-laying animals/animals in general.
The Sibley Guide to Birds
Amazon Price: $26.37 (as of 01/07/2010) 
The Sibley Field Guide to Birds of Eastern North America
Amazon Price: $13.57 (as of 01/07/2010)
A Field Guide to Reptiles & Amphibians of Eastern & Central North America (Peterson Field Guide Series)
Amazon Price: $14.28 (as of 01/07/2010)
National Audubon Society Field Guide to North American Insects and Spiders (National Audubon Society Field Guides)
Amazon Price: $13.57 (as of 01/07/2010)
Animal: The Definitive Visual Guide to the World's Wildlife
Amazon Price: (as of 01/07/2010)
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