Blog # 269 Countdown to Hatch Day

 The hatching of an Osprey egg is a beautiful process. In just five weeks, a fertilized egg transforms into a complete, live baby bird. The climax of this transformation, the hatching of the baby Osprey, usually occurs in the early morning. The average incubation period for Osprey eggs is 37 days, which makes Ophelia’s first egg due to hatch on or after May 19—tomorrow—with the others following a few days apart in the order they were laid. 

Osprey embryocracking (external pipping) the shell to crack it open, courtesy of Dfyi. 

As incubation draws to an end, the embryo fills nearly the entire egg. However, this is not the most important trigger for the start of the hatching process. As incubation draws to a close, the embryo 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.) However, the embryo’s oxygen demand increases along with its growth and activity while oxygen supplies from the CAM run short. 

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. A few days before hatching,  the embryo pierces the inner membrane and starts lung ventilation in the air pocket. 

Cross section of an bird egg showing the Air pocket, courtesy of Brainly.in. 

This is called internal pipping. Even though the first lung respiration has started, the  CAM remains important for respiration for a few more days.  

A few days before hatching, an embryo will start peeping, communicating with its sibling embryos and its parents, from inside the egg. These faint “care-soliciting” peeps prompt the adults to turn the eggs more often, build up the nest sides, and spend more time incubating.  

About 12 hours after it pierces the inner membrane, it starts tapping the eggshell repeatedly with its egg tooth, a sharp and a strong albeit temporary structure on the top of the beak. Repeatedly tapping the eggshell in the same spot causes the shell to weaken and eventually break. 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 embryo takes a rest. It has one last challenging task ahead:  breaking free from the eggshell. It normally takes another 12 hours after external  pipping to hatch. To do so, the embryo starts cutting the eggshell with the 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 near 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  

Osprey nestling (top) and hatching in progress below, courtesy of Alan F. Poole. 

cap to break loose, allowing the embryo to push itself free. New hatchlings are wet,  tired, and vulnerable. Hours after hatching their down feathers dry, and they become  fluffy. After they’ve recovered from the hatching process they become more active.  

The hatchling used its “egg tooth” (black growth on upper beak) to crack 

the egg shell, courtesy of OspreyWatch.

Note the size difference between two nest mates born 2 days apart, courtesy of CU Maurice River. org. 

Ospreys are semi-altricial birds, meaning their young are born nearly helpless, but not  completely, and unable to thermo-regulate their body temperature. The hatchlings are capable of limited motion, are covered with down, and have their eyes are open. Altricial eggs are smaller than the eggs of precocial species. That is because precocial species are completely developed when they hatch where as the altricial birds have more development to complete.  

Ospreys lay their eggs serially 2–3 days apart, producing hatchlings of graduated sizes.  If fish suddenly become scarce threatening the brood, brood reduction (the sacrificing of the youngest hatchling through sibling rivalry) is employed to ensure the more robust nestlings survive. Fortunately, Cayuga Lake offers a fairly consistent supply of fish throughout the Osprey season making brood reduction unnecessary. 

Eyes to the sky! 

Candace

Candace E. Cornell  

Friends of Salt Point  

Lansing, NY 

ALL EYES ON OSPREYS 

WATCH! 

Salt Point Osprey Nest Cam 

READ! 

On Osprey Time 

Ospreys of Salt Point 

VISIT! 

Cayuga Lake Osprey Trail

Comments

Post a Comment

Popular posts from this blog

Blog #481 Sunshine at Last!

Image
  Last week’s 2 week old chicks. Now they look completely different, courtesy of Facebook. Meteorologists report this is the 6 th  day of sun in all of May with more rain in the forecast. This is good for the plants but potentially damaging to the Ospreys. Foul weather rots eggs and makes hunting difficult to impossible at a time when the hatchlings are most vulnerable to the starvation, cold, and predation. Despite the challenges of fishing in windy, rainy conditions, Orpheus succeeded in keeping the family fed by catching small, nearshore fish and making up for deficiencies with large trout whenever there was a break in the weather. A foggy morning feeding the 2 ½ week-old chicks, Salt Point Osprey Nest Cam. The 3 week-old chicks in their reptilian phase, courtesy of YouTube. Oakley, the eldest chick, just turned two-weeks old and is passing into the Reptilian Phase,  where the now darker, scaly chicks. In this transitional phase Oakley’s buff down is quickly replaced w...
Read more

Blog #482 Where Ospreys are Starving

Image
Male Osprey landing a beauty, enough to feed the entire family trout, courtesy of Patrick Marshall. Ospreys of the Cayuga Lake Osprey colony, live in the stunning heart of New York’s Finger Lakes of a terrific about centered on Cayuga Lake may lull us into complacent thinking that all is well in their world. Life for Ospreys near Cayuga is certainly good for our in this inland colony with lots to eat and seeming endless nesting possibilities, but an ecological tragedy is in the making not far away. Osprey chicks are starving and whole colonies collapsing in the Chesapeake Bay region, home of the world’s highest concentration of breeding Ospreys (until recently estimated at 10,000 breeding pairs). The tragedy is caused by a sharp decline of their dietary staple, menhaden, called “the most important fish in the sea” by author H. Bruce Franklin. Ospreys, striped bass, bluefish, weakfish, whales, and a myriad of other coastal and marine species dependent on menhaden for food are all declin...
Read more

Blog #461 Sneak Peek at Osprey Season 2024

Image
  Orpheus (L) and Ursula at their Salt Point Nest March 26, courtesy of Cindy Sedlacek. The following is a sneak peek at what this Osprey summer will entail. Our northeastern Ospreys return to their breeding habitats just after the early spring thaw. This year’s first Osprey was seen in Cayuga Lake Basin on March 15, an early date many attribute to  the mild winter. Most nest occupants will have returned to their nests and reunited with their mates by this weekend. These returning Ospreys have just completed their 2,000–4,000-mile migrations from their wintering areas along the coasts of South America and in the wild Amazonian tropics. The range of landscapes that a cosmopolitan Osprey can experience in its lifetime is staggering. In general, the older breeding males arrive on their nests followed by their mates in a few days. After that first wave of older Ospreys arrive, unmated adults and second-year birds migrating north for the first time after spending two years in the S...
Read more