Hatching is still a few weeks away but this picture by Jim Cruce gives a preview of what is to come!
The South Waterfront Osprey are now on their 19th day of incubation. It takes 36-42 days to hatch so we are at approximated the halfway point. For those that were used to watching the Raptor Cam Red-tails in prior seasons, it probably seems like a really long haul. The Osprey start their nesting later and have a longer incubation period. In fact, the red-tails young would already be almost half grown by this point in the season. The osprey's nesting chronology will take us well into the summer whereas the red-tails was pretty much over by early June.
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 osprey 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 hatch while atricial birds spend additional time --for osprey usually about seven-eight 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.