The peregrines started the day under clear skies with a few clouds, light winds and temp at 53F around 7AM.  The photo shows the female towards the end of the while incubating the eggs and preening.

So how do birds hatch?

The embryo has breached the membrane, is breathing air with its lungs, and is head up, with its head positioned at the large end of the shell.

• Our embryo  uses its egg tooth, a small temporary structure on the op of its beak, to cut through the shell from inside. The eggshell is thinner and weaker than when it was laid, since the growing embryo absorbed calcium from the shell for its bones. The embryo rubs its egg tooth against the shell, which cuts a small hole.
• As it rubs it rotates its body, slowly cutting a ring around the shell.
• When the cut is complete, the hatchling bird pushes its body against the shell, forcing it apart.  It works itself free of the shell membranes and halves. Voila – a baby bird!

Literature cited:

The Raptor Research Project, Raptor Research Project Blog, Saturday, March 10, 2012                                                                                                                        https://raptorresource.blogspot.com/2012/03/

This morning the peregrines started the morning with a bit of fog, light winds from the NE, and temp at 46F.  The day ahead calls for sunny skies, with a high near 71. Calm wind becoming south 5 to 8 mph in the afternoon.  At 6:44 AM the male was incubating the eggs, and acted in usual restless way. He moved around quite a bit, shaking side to side, and rocking back and forth, nibbling at bits of gravel, and turning.  A bit later as the sun came out after the morning fog, the female was seen outside the nest box on the perch….another sign that hatching is close!

We are getting a lot of questions about eggs and hatching.  It takes about 29-31 days for Peregrine Falcon eggs to hatch, 35-37 days for Bald eagle eggs to hatch, and about 28 days for great horned owl eggs to hatch. Despite the differences in incubation times, very similar things happen in the eggs of all three species. 

What happens within the egg shortly before hatching starts?

The rapidly developing embryo…

• Grows large enough to take up nearly all the space.
• Positions its body so that its head is at the large end of the egg next to the air space.
• Begins to breathe with its lungs. Ever crack an egg and see the white membrane inside? Before the chick pokes its beak through this membrane into the air space, a special tissue called the CAM supplies oxygen to the developing embryo. Gases, including oxygen, leave and enter 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 the CAM. From there, the blood circulates through the embryo and provides it with oxygen – no lungs required until the membrane is broken. 
• Consumes most of the remaining albumen and yolk. When I was young, I thought that birds formed from the yolk. Not so! The yolk provides food and energy for the embryo.

The chart below outlines major developmental points in the lifecycle of a developing chicken embryo. At 20 days, the chicken is almost large enough to break the membrane and begin hatching. The timing would be a little different in the case of Bald eagles, Canada geese, and Great Horned owls, but the stages of development are the same.

Literature cited:

The Raptor Research Project, Raptor Research Project Blog, Saturday, March 10, 2012                                                                                                                        https://raptorresource.blogspot.com/2012/03/

The peregrines started the day off with overcast skies, light rain, winds from SW at 5MPH, and temps in low 60’s.  The day ahead calls for showers, mainly before 1pm. High near 64. Light and variable wind becoming northeast around 6 mph in the afternoon. Chance of precipitation is 90%. New precipitation amounts of less than a tenth of an inch possible.

A cold front slid through the area last night accompanied by a few thunderstorms and showers as it passed through the area, with some gusty winds exceeding 50mph!  This biggest thing to notice heading out today is that it is much less humid! A much drier air mass will be over us today.   The forecast calls for the day to start out breezy with sunshine and scattered clouds early…temps jump into the low to mid 70’s by this afternoon along with increasing clouds and diminishing winds.  Late day sunshine is expected!

The female was seen incubating eggs late afternoon just before 5:30 PM.  She was awake and gently looking around while making every effort to protect the eggs from the late day sun,  Something caught her attention and she lifted her head up, straightened her neck and went into a state of higher alert.  She rose up and turned to her left to look out to the west, alerted to some disturbance.

In cases like this, a passing bird predator may draw the incubating falcon from its eggs.  Much depends on whether the off-duty partner is nearby.  Even if it remains silent, the sitting falcon will nearly always see the mate and will doubtless recognize alarm signals from its manner of flight.  The female, remained on lower alert level after looking out, but still seemed to keep a sharp eye on whatever was going on outside the nest box!

Literature cited:

Ratcliffe, D. 1993. The Peregrine Falcon. 2nd ed. Carlton, England: T. and A. D. Poyser.

Sunrise time this morning at 5:36 AM.  Morning weather conditions:  cloudy, wind from W at 6MPH, 70F.

Forecast for day ahead: a chance of showers and thunderstorms, mainly after noon. Some of the storms could produce gusty winds and heavy rain. Mostly cloudy, with a high near 84. West wind 6 to 10 mph, with gusts as high as 23 mph. Chance of precipitation is 40%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Around 5:48 AM, the female rose up, and departed in flight from the right side of the nest box.  Almost two minutes later the male enters the nest box, moves around, pushes the gravel around, shakes side to side, and rocks forward and back.  He always seems to take quite a bit longer to settle in on the eggs.

This morning the peregrines started the day with clear skies and lots of sunshine, with winds on the lighter side from the SW at 7MPH and the temp at 55F.

The female had been holding down the overnight incubation duties.  At 5:32 AM, she rose up and off the eggs, headed to the left edge of the nest box, and departed.  Minutes later, the male entered and did his usual and extended shake, rattle, and roll before finally settling on the eggs.  The incubation total coverage by both male and female has been terrific. Contact incubation of eggs is one of the most conspicuous features of avian biology.  Its purpose is the maintenance of a warm and steady egg temperature, and the parents adjust their lives around this entire objective.

The transfer of heat onto the eggs is regulated  through adjustments to blood flow through the previously mentioned brood patch, and heat production by the parent, mediated through temperature sensors in the skin of the brood patch.  It s all about the maintenance of a steady egg temperature!