Bird Eggs
SizesBird eggs vary hugely in size, like the birds themselves.The largest egg produced in the bird kingdom is that of the ostrich egg – weighing up to...
Sizes
- Bird eggs vary hugely in size, like the birds themselves.
- The largest egg produced in the bird kingdom is that of the ostrich egg – weighing up to 1.2kg.
- The smallest egg produced in the bird kingdom is that of the hummingbird – weighing half a gram.
- So ostrich eggs are 2000 times the size of hummingbird eggs!
- The elephant birds of Madagascar, now extinct, laid eggs about 14 inches long with a capacity of about 2 gallons – much bigger than ostrich eggs.
- The first and last set of eggs produced by chickens tend to be smaller than the others.
Quantity
- The name for one or more eggs produced by a bird in a nest at one time is the clutch.
- Some of the penguins, albatrosses and other sea birds that nest in inaccessible places lay only one egg in a clutch.
- Wild ducks and game birds such as quail and pheasants, which have numerous enemies, lay 15 or more in a clutch.
- Most songbirds lay from 3 to 5, although hole-nesters like chickadees may lay 8 or more; tropical species seem to lay fewer eggs than their northern relatives.
- Hawks and owls lay more eggs when their prey is plentiful.
- Clutch size may also differ within the same species due to many factors including habitat, health, nutrition, predation pressures, and time of year[.
- Long lived species tend to have smaller clutch sizes than short lived species.
- The evolution of optimal clutch size is also driven by other factors such as parent-offspring conflict – when the parents and children have to compete for resources.
Shape
- The fancy math words to describe an egg shape are oblate spheroid.
- The word spheroid means that the egg is like a sphere, but isn‘t exactly a sphere. That‘s because an egg isn‘t perfectly round.
- This shape results from the egg being forced through the oviduct. Muscles contract the oviduct behind the egg, pushing it forward.
- Cliff-nesting birds often have highly conical eggs. They are less likely to roll off, tending instead to roll around in a tight circle; this trait is likely to have arisen due to evolution via natural selection.
- Many hole-nesting birds have nearly spherical eggs.
Anatomy
- Inside an egg you have three main areas: the air cell, egg white and the yolk.
- The air cell tends to be at the larger end of the egg.
- The air cell is caused by the contraction of the egg contents as it cools after laying.
- The air cell tends to get bigger and bigger as the egg ages and the embryo develops.
- The egg white is called the albumin.
- The albumin has two main layers – the inner (thin albumen) and the outer (thick albumen).
- The albumin‘s primary natural purpose is to protect the yolk and provide additional nutrition for the growth of the embryo.
- The albumin is 90% water.
- The albumin is rich in proteins and also of high nutritional value but doesn‘t contain much fat.
- The egg yolk contains the growing embryo and its main food source – the yolk.
- The yolk is an energy-rich supply of food for the embryo.
- The yolk is suspended in the middle of the egg by strands known as chalazae.
- Egg yolk is yellow because it contains a lot of carotenoids.
- Carotenoids are organic pigments that protect vulnerable tissues against damage caused by free radicals.
- Free radicals atoms, molecules, or ions with unpaired electrons on an otherwise open shell configuration – these unpaired electrons are more unstable and highly reactive to other elements, causing chemical reactions.
- Inside the egg yolk the embryo is surrounded by three membranes: the amnion, the chorion and the allantois.
- The amnion surrounds the embryo and provides fluid in which is floats and grows.
- The allantois is next to the amnion and helps the embryo breathe and excrete wastes.
- The chorion serves as a membrane around the egg yolk.
Shells
- The outside of an egg is known as the shell.
- Egg shells are porous – having thousands of pores hat allow gas to come in and out of the egg itself.
- Egg shells get their colors from pigments added when the egg passes through the oviduct.
- The original color of bird eggs is white but egg colors have evolved through natural selection to suit their surroundings – mainly to camouflage them when it is necessary.
- Egg shells are generally white in cavity-nesters as they don‘t need to be camouflaged.
- Egg shells are colored and patterned in open nesters as they need to be camouflaged.
- Sun radiation is also a factor in the determination of bird egg colors.
- Birds that nest in huge colonies tend to have very varied eggs – extremely variable in color and size. This would tend to suggest that this helps the parents find their eggs.
- Some of the pigments used in speckled eggs have now been proven to strengthen the egg shell.
- Passerine birds (perching or song birds) tend to have more variety in their egg shell speckling than other kinds of birds.
- Research shows that birds nesting in areas of the woods where the soil is known to be low in calcium produce eggs that are more heavily speckled.
- South American game birds, have solid metallic colors and a finish like that of a new automobile.