Blog # 464 Hatching Starts Days Before the Egg Cracks (revision of #436)
Osprey embryo cracking (external pipping) the shell to crack it open, courtesy of Dfyi.
The hatching of an Osprey egg is miraculous process. In just five weeks, two cells divide and transform into a graceful hunter and ruler of the sky. The climax of this transformation, the hatching of the baby Osprey, usually occurs in the morning. Ursula’s eggs hatch in the order they were laid with the first two eggs hatching on May 11th and 13th and the last egg is ready to hatch tomorrow.
Towards the end of incubation the growing embryo nearly fills the entire egg and starts to retract the residual yolk into its body cavity. Until that point, the embryo has used the chorio-allantoic membrane (CAM) for respiration, diffusing CO2 and O2 through the eggshell and the CAM. (The CAM is represented by the chorion membrane in the illustration below.) The embryo’s oxygen demand increases along with its growth and activity while oxygen supplies from the CAM run low.
The shortage of oxygen triggers the embryo to start lung respiration. The embryo instinctively puts its head under its right wing with the beak pointing toward the membrane separating the egg contents from the air pocket. Its beak pierces the inner membrane allowing the chick to breathe air from the air pocket. This is called internal pipping. Even though lung respiration has started, the CAM remains important for respiration for a few more days.
A few days before hatching embryos start peeping, communicating with its sibling embryos and parents from inside the egg. These faint “care-soliciting” peeps prompt the adults to turn the eggs more often, which get heavier every day, and spend more time incubating. The parents also build up the sides of the nest to contain the hatchlings.
After 12 hours of pipping the embryo pierces the inner membrane and begins tapping on the eggshell with its egg tooth (see photos below), a sharp,strong temporary structure on the top of its beak. After hours of repeatedly tapping the same spot on the eggshell it eventually weakens and breaks. This is called external pipping. Pipping demands great effort. The pipping muscle, a neck muscle used to make this specific movement, is bulging by the time the embryo has finished hatching. From the outside, a small star-shaped crack or hole in the eggshell appears 2–3 days before hatch day, sometimes with the point of a beak sticking out.
After external pipping, the exhausted embryo rests. It has one last challenge: breaking free from the eggshell, which normally takes another 12 hours after external pipping. To get out, the embryo starts cutting the eggshell with its egg tooth. While cutting, the embryo turns around inside the egg, using its wing for direction and legs to apply force.
Once it has cut a circle at the blunt end of the egg, the embryo tries to push itself out of the egg stretching its legs. This causes the last bit of the shell, the cap, to break loose, allowing the embryo to push itself free. New hatchlings are wet, tired, and vulnerable, but once rested and dried off, they are are ready for the dinner.
Towards the end of incubation the growing embryo nearly fills the entire egg and starts to retract the residual yolk into its body cavity. Until that point, the embryo has used the chorio-allantoic membrane (CAM) for respiration, diffusing CO2 and O2 through the eggshell and the CAM. (The CAM is represented by the chorion membrane in the illustration below.) The embryo’s oxygen demand increases along with its growth and activity while oxygen supplies from the CAM run low.
The shortage of oxygen triggers the embryo to start lung respiration. The embryo instinctively puts its head under its right wing with the beak pointing toward the membrane separating the egg contents from the air pocket. Its beak pierces the inner membrane allowing the chick to breathe air from the air pocket. This is called internal pipping. Even though lung respiration has started, the CAM remains important for respiration for a few more days.
Cross section of a bird egg showing the air pocket, courtesy of Brainly.in.
After 12 hours of pipping the embryo pierces the inner membrane and begins tapping on the eggshell with its egg tooth (see photos below), a sharp,strong temporary structure on the top of its beak. After hours of repeatedly tapping the same spot on the eggshell it eventually weakens and breaks. This is called external pipping. Pipping demands great effort. The pipping muscle, a neck muscle used to make this specific movement, is bulging by the time the embryo has finished hatching. From the outside, a small star-shaped crack or hole in the eggshell appears 2–3 days before hatch day, sometimes with the point of a beak sticking out.
After external pipping, the exhausted embryo rests. It has one last challenge: breaking free from the eggshell, which normally takes another 12 hours after external pipping. To get out, the embryo starts cutting the eggshell with its egg tooth. While cutting, the embryo turns around inside the egg, using its wing for direction and legs to apply force.
Once it has cut a circle at the blunt end of the egg, the embryo tries to push itself out of the egg stretching its legs. This causes the last bit of the shell, the cap, to break loose, allowing the embryo to push itself free. New hatchlings are wet, tired, and vulnerable, but once rested and dried off, they are are ready for the dinner.
Nestling with camouflaged stripe (top) and hatching below, courtesy of Alan F. Poole.
The hatchling used its “egg tooth” (black growth on upper beak) to crack
the egg shell, courtesy of OspreyWatch.
Note the size difference between the hatchlings born 2 days apart, by CU Maurice River.org.
Birds hatch in one of three states: altricial, precocial, or semi-altricial according to their stage of development when leaving the egg. Naked altricial birds, like wrens and robins, usually have smaller eggs than feathered precocial species (geese and ducks) because they need more time to develop after hatching.
Osprey hatchlings are semi-altricial birds, born nearly helpless, but not completely. The hatchlings are born down-covered with open eyes, and capable of limited movement. However, the young are unable to thermoregulate their body temperatures and are dependent on their parents for warmth.
The size of Ursula’s eggs reflected the order in which they were laid, and predicted the size of her hatchlings. Starting with the eldest and largest, the hatchlings are of graduated sizes with slightly less nutrition going to each progressively smaller egg.
These size differences become vitaly important if the supply of fish tanks. Normally, a hierarchy of size forms as soon as the Osprey eggs hatch, with the largest, most demanding hatchling getting fed first, and the smallest, least demanding chick feeding last. For instanced, if Orpheus brought a small fish to the nest, the smallest hatchling might not get fed.
If food becomes suddenly scares during the fledging period, brood reduction, the sacrificing of the youngest hatchling(s) through sibling rivalry, may occur. Siblicide is bloody and difficult and bloody to watch, as the parents stand aside, letting the larger chicks peck their weaker nestmate to death. Cruel as it may seem, Ospreys only exercise brood reduction when the lack of food makes it necessary to ensure the survival of their most robust nestling. The alternative would be raising a brood of mediocre young with little chance of surviving. Many other raptor species regularly employ obligate siblicide or Cainism to cull their brood. A few days after hatching the larger chick will kill the smaller one.
Thankfully, Cayuga Lake offers an ample supply of fish available to the Osprey throughout its breeding season making brood reduction unnecessary. However, Osprey populations breeding in coastal areas are more dependent on fish migrations, which are being impacted by overfishing.
Osprey hatchlings are semi-altricial birds, born nearly helpless, but not completely. The hatchlings are born down-covered with open eyes, and capable of limited movement. However, the young are unable to thermoregulate their body temperatures and are dependent on their parents for warmth.
The size of Ursula’s eggs reflected the order in which they were laid, and predicted the size of her hatchlings. Starting with the eldest and largest, the hatchlings are of graduated sizes with slightly less nutrition going to each progressively smaller egg.
These size differences become vitaly important if the supply of fish tanks. Normally, a hierarchy of size forms as soon as the Osprey eggs hatch, with the largest, most demanding hatchling getting fed first, and the smallest, least demanding chick feeding last. For instanced, if Orpheus brought a small fish to the nest, the smallest hatchling might not get fed.
If food becomes suddenly scares during the fledging period, brood reduction, the sacrificing of the youngest hatchling(s) through sibling rivalry, may occur. Siblicide is bloody and difficult and bloody to watch, as the parents stand aside, letting the larger chicks peck their weaker nestmate to death. Cruel as it may seem, Ospreys only exercise brood reduction when the lack of food makes it necessary to ensure the survival of their most robust nestling. The alternative would be raising a brood of mediocre young with little chance of surviving. Many other raptor species regularly employ obligate siblicide or Cainism to cull their brood. A few days after hatching the larger chick will kill the smaller one.
Thankfully, Cayuga Lake offers an ample supply of fish available to the Osprey throughout its breeding season making brood reduction unnecessary. However, Osprey populations breeding in coastal areas are more dependent on fish migrations, which are being impacted by overfishing.
Eyes to the sky!
Candace
Candace E. Cornell
Cayuga Lake Osprey Network
Lansing, NY
EYES TO THE SKY!
WATCH!
READ!
On Osprey Time: Ospreys of the Finger Lakes
VISIT!
Cayuga Lake Osprey Trail Nests Driving Tour
Complete Cayuga Lake Osprey Trail
HELP PROTECT OSPREYS:
•Stay 300 feet away from nests during the breeding season.
If the Osprey vocalizes, you are too close!
Back off Immediately.
•Carry binoculars to view wildlife from afar.
•Help keep local waters clean, healthy, and safe.
•Recycle used fishing lines, twine, and nets, which can kill Osprey.
•Join the Cayuga Osprey Network and volunteer to help monitor Osprey nests: cec222@gmail.com.
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