Incubation

Female of Oberhausen turning her eggs

Incubation

For an egg to develop normally, it must be exposed for a considerable length of time to temperatures a few degrees below the normal 104 degrees F (40 degrees C) avian body temperature. Indeed, the ideal incubation temperature for many birds' eggs is about human body temperature, 98.6 degrees F. Almost all birds create the required temperature by sitting on the eggs and incubating them, often transferring heat via a temporarily bare area of abdominal skin called the "brood patch."

On the other hand, the embryo inside the egg is also very sensitive to high temperatures, so that in some situations eggs must be protected from the sun. Peregrines often stand over the nest and shade the eggs when temperatures rise.

Embryos are less sensitive to cold than to heat, particularly before incubation has started. Some eggs have been known to crack by freezing and still hatch successfully. Eggs cool when incubation is interrupted, but this is not usually harmful, and few birds incubate continuously. Instead egg temperature is regulated in response to changes in the temperature of the environment by varying the length of time that a parent bird sits on them or the tightness of the "sit."

Peregrines apparently sense the egg temperature with receptors in the brood patches, which helps them to regulate their attentiveness (time spent incubating) more accurately. Since the embryo itself increasingly generates heat as it develops, periods of attentiveness should generally decline as incubation progresses. Attentiveness is also influenced by the insulating properties of a particular nest.
Eggs are also turned periodically -- from about every eight minutes to once an hour.
The turning presumably helps to warm the eggs more evenly, and to prevent embryonic membranes from sticking to the shell.
Both parents incubate. But there is a large difference in time they spent doing so. Males incubated about 3o% of time, with attentive periods of 2–3 h; female attentive period is about 4 h and she incubates 70% of the time.

Both parents are needed in this incubationproces. Because the Peregrine is a bird of prey, food is not somewhere around the corner to pick up. Hunting is required. Given the fact that only 1 in 4-5 hunt attempts are succesvol in striking prey, it's rather time comsuming. The male therefor is the one who hunts. He is smaller, can move faster and is therefor more succesful in hunting than the larger female is. He has proven her during courtship that she can fully rely on him during incubation and later on when the eyas are born, she knows he can provide. That's why she has choosen him, not because of his beautiful brown eyes !

So he is the one who hunts and takes care of the groceries. It's therefore disastrous when anything happens to him during the incubation. She will not be, or hardly be able to incubate and takes care of food at the same time.

Food is not eaten in the nest, but outside. He flies by with food and she leaves the eggs. He takes over incubation, while she eats. And.... of course goes to the bathroom. Afters hours of incubation she really has to go. She can not leave her droppings close to the eggs, because of the infectionrisk. Sanitation is essential for the health of her unborn children. And so she has to sit on a full blatter until he appears.