If you’re a casual observer of the Arboretum’s live osprey cam, it isn’t easy to spot eggs with the parents sitting on (incubating) the eggs most of the time. (Yes, both parents do this job.)
But one of our nest fans recently shared her photo with us of three eggs, along with a question:
Q: It looks like there are three egg-shaped objects in the nest but they are very dark. Are they muddy from the nest? Or is that what they might look like if they are rotting? I’ve never seen eggs in a nest that appear dirty. — Mary Beth
A: “Great question!” said Lori Arent, the Assistant Director of The Raptor Center at the College of Veterinary Medicine at the University of Minnesota.
“When most people think of bird eggs, they envision the solid white shells of commercially produced chicken eggs.
“Different breeds of chickens can have different colored eggs, as it is all in their genetics. The eggs of wild birds can be different solids colors or have a variety of pigment that is added as the egg passes through the oviduct (the tube an eggs moves into when released from the ovary). Osprey have soft white/off-white egg shells, but they are marked with spots and streaks of color as they pass through the oviduct, making them each different from each other.
“In other words, some have more pigment than others. Glands in line lining of the oviduct produce the pigment, and if the egg is stationary as it touches the gland, pigmented spots will appear on the shell; if the egg is moving when it touches, it will have streaks. “
“For birds that nest in the open like osprey, having irregular pigments on their eggshells helps the eggs to blend in with the nesting material to help protect them from potential predators. So, the eggs of this osprey pair are normal!”
Thank you for the question (and the family photo), Mary Beth, and please keep them coming. Fingers crossed for successful hatching. Here's a shot from today showing the eggs in a different light.
