An unfertilized chicken egg.
The eagle egg in the Eagle Cam nest.
Why are eagle eggs sometimes left "unincubated"?
How do you know if an egg will survive?
What is the science behind the incubation process?
Most Eagle Cam fans have wondered these questions. In response, we want to highlight Raptor Resource Project, a nonprofit specializing in Raptor education and preservation, as they kindly illuminate the mysteries behind eggs and incubation.
Unlike most birds, chickens will lay eggs even when a male isn't present. We'll start with a quick look at an unfertilized egg, pictured above. From the Chicken Chick: An infertile egg contains only the hen's genetic material, which means a chick can never hatch from that egg. The hen's genetic material, termed the blastodisc, can be identified on infertile eggs as a light-colored dot with irregular borders. Every egg contains a blastodisc. The chicken eggs we have for breakfast (up top) are infertile. The blastodisc can be seen in the center of the egg. If the egg is fertilized, the blastodisc turns into a blastoderm; the first stage of embryonic development. End stage? Hatchling bird!
Let's assume we have a fertilized egg. As the embryo develops, it will consume both the fatty egg yolk and high-protein egg white. By the end of day two, our little chicken will have a heartbeat. Its beak and egg tooth will begin to form on day six, and its feathers on day eight. By day nine, it will begin to look somewhat like a bird, and its mouth opening will form.
So what does the developing embryo need to survive? Yes, temperature is vital, but incubating birds (or incubationist humans) also need to control humidity, move or turn the eggs, and make sure the eggs are well-ventilated.
Keeping Eggs Alive
Why are eggs sometimes seemingly left unattended? The eagles may have been giving the eggs a chance to dry out and breathe. A bird's eggshell has thousands of tiny pores, which allow water and gas to pass through. Mammals like us get oxygen through an umbilicus, but developing birds receive oxygen and remove carbon dioxide through the eggshell. Gases, including oxygen, enter and leave the egg by diffusing through the pores in its shell, across the outer and inner shell membranes, and into the blood in the capillaries of a special tissue called the CAM, or chorioallantoic membrane. As the weather warms, the snow begins to melt and humidity levels soar. Condensation can form on eggshells exposed to excessive humidity, which clogs shell pores and provides a vehicle for bacteria. The result? Fatal suffocation and/or contamination. Only the eagles know for sure, they may respond to the threat of rising humidity levels by leaving their eggs uncovered. Standing or leaving entirely allows fresh air to circulate over the eggs, dropping the humidity level and giving the developing embryos fresh air. Turning or rolling assists air exchange, helps maintain an even egg temperature (especially in big egg piles, where outer eggs may be cooler than inner ones), and keeps the developing embryo from sticking to the eggshell.
In short, most bird eggs require specific temperatures, proper humidity, regular movement, and air exchange. Birds provide these by applying body heat, standing and/or leaving for periods of time, and rolling or turning their eggs. In birds, incubation is both an instinctive and learned behavior - while birds will automatically incubate eggs or egg-shaped things, they get better at incubation with experience. There are no guarantees, but Mom and Dad are skilled incubators. Watching them meet the challenges of their environment gives watchers hope for their eggs. Go eagles!
Founded in 1989, The Raptor Resource Project is a nonprofit that specializes in the preservation of falcons, eagles, ospreys, hawks, and owls. They create, improve, and directly maintain 50+ nests and nest sites, providing training in nest site creation and management while developing innovations in viewing and management; bringing people closer to the natural world. Their mission is to preserve and strengthen raptor populations, expand participation in raptor preservation, and help foster the next generation of preservationists.
The text in this blog has been adapted and posted with permission from The Raptor Resource Project Blog.
View original blog post here.