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March 6, 2011: Eggs

March 6, 2011: Eggs

Credit: Bob Sallinger

by Bob Sallinger

kgw.com

Posted on March 6, 2011 at 10:36 AM

Updated Wednesday, Oct 30 at 9:31 AM

As of March 6th the hawks still have not laid their first egg. Again, no cause for concern. The onset of egg laying in red-tails can vary extensively from year to year. The weather has been awful and that may affect the timing.

Since the Raptor Cam Red-tails took up residence in 2007, the dates they have laid their first eggs have ranged from March 3rd to March 16th. Some  raptor species are already well into their nesting cycle--Audubon's Wildlife Care Center took in its first nestling barn owl this week!

Other species like osprey have not even returned yet on their spring migration. In the Metro region we get red tails laying eggs as early as March and as late as April.

The Raptor Cam Red-tails continue to add to the nest ---note all the new green material in the nest today---so odds are that they will be using this site in the near future.The greenery serves several functions--it provides insulation for the eggs, provides a buffer between the eggs and all the debris from last years nesting cycle, and has insecticidal properties.

Watch Live: Raptor Cam

Greenery in the Nest March 6, 2011

A few words about the egg: The egg is basically a vehicle to nourish and protect the embryo until it is developed enough to survive in the environment.  Some birds like red-tailed hawks are atricial meaning that even after they hatch, they are relatively helpless and are completely dependent on their parents for survival. Other bird species such as killdeer and Canada geese are precocial meaning that they emerge from the egg in a fairly advanced state of development and are able to walk and self feed almost as soon as they emerge. Precocial birds usually leave the nest and follow their parents around on the day that they emerge while atricial birds spend additional time --for red-tails usually about six weeks--in the nest continuing to develop.

The main structures of the egg are the yolk, albumen (egg white) and shell. The yolk is a food source for the growing embryo. It is loaded with fat globules and protein. The albumen (or egg white) is a viscous fluid that surrounds the embryo and the yolk and serves as a shock absorber for the embryo which sits on top of the yolk. The shell is comprised of three layers and serves to protect for the egg. It is porous and allows for gas exchange with the outside environment. Several local species including peregrines, osprey and bald eagles were almost lost because the pesticide DDT which was used during the 1940, 50s and 60's blocked an enzyme in birds necessary to create calcium and these species laid eggs with thin eggshells which cracked during incubation. The embryo which will eventually become a bird, begins as only a millimeters in length but grows rapidly. By ten days it is already beginning to look like a bird in shape.

The size, shape, number and color of eggs varies greatly among different species. A hummingbird egg weighs 0.3 grams while and ostrich egg can weigh as much as 1600 grams. Coloration patterns often serve as camouflage to hide the egg from predators.

 

 

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