Our story thus far: The female Bald Eagle has laid two eggs this season, on 2/16-17 and 2/20.
A box without hinges, key, or lid, Yet golden treasure inside is hid." -- J.R.R. Tolkien, The Hobbit
With the arrival of eggs in the Duke Farms Bald Eagle nest, the nervous season has begun. Two eggs -- no snow but cold temperatures. Eagle Cam viewers can get nervous when the adults leave the eggs. Watching the two adult eagles incubate the eggs -- a process that typically takes five weeks -- can often seem a bit ho-hum. But when the eggs are left unattended in colder weather -- even for a short spell -- it can be nail-biting time. So lets address that big question right away: Should folks be worried when both eagles leave the nest? Weve had several inquiries about this, and we had similar concerns when we first started watching the camera after it was installed, says Thom Almendinger, Duke Farms Director of Natural Resources. This is a replica Bald Eagle egg photographed next to a U.S. quarter (eagle side up) for size comparison. But this is an experienced pair that has successfully hatched 19 or 20 of the 21 eggs it has produced. The adults instinctively know to sit on the eggs when they need heat and get off them when they need to be cooled. Kathy Clark, a wildlife biologist for the N.J. Endangered and Nongame Species Program adds: Eggs are okay getting chilled for the first few days, before there is much development. They can't freeze, though, without some permanent damage to the embryo. In short, this is wild nature and nothing is certain, but there may be bigger things to worry about. Now, a few egg fundamentals. Eagle eggs may look small in the nest, but they are larger than many folks might think. The eggs, a dull white or off-white, are the size of lop-sided tennis balls and weigh a quarter of a pound.
The egg counts for the Duke Farms nest for the past 10 years have ranged from one to three. Last year the adults incubated three eggs. The female keeps the eggs warm most of the time, especially until all the eggs have arrived, but the male does help out. Male turns the eggs. We can tell he is the male because he is leg-banded and this female is not. Both adults also turn the eggs from time to time -- to regulate them at the correct temperature and prevent the embryos from sticking to the inside of the eggshell, says Thom. To help keep the eggs warm easier, the male and female can develop a brood patch. Conserve Wildlife Foundation of New Jersey describes the patch as a small featherless area on their chest .... well-supplied with blood vessels. making it possible to transfer heat to their eggs during incubation. What should Eagle Cam viewers watch for during this part of the nesting season? The way the adults curl their talons under while walking around the egg, says Thom, and the way they wiggle as they position the egg underneath them. And for this particular pair, youre watching a very attentive male who actually is very particular about nest-tending.
Tomorrow (Bonus Post): A Brief and Relatively History of Bald Eagle Eggs in New Jersey.
Next week: All about the Duke Farms Bald Eagle nest.
Last week: Bald Eagle basics.
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Jim Wright writes The Bird Watcher columnist for The Record and the Herald-News. He is the author of four coffee-table books about wild places, and the deputy marsh warden of the Celery Farm Natural Area in Allendale, N.J.