Why isn’t she sitting on the eggs?

Two eggs at Gulf Tower peregrine nest, Pittsburgh, 2008This photo of a peregrine nest with no mother bird sitting on the eggs prompted several of you to ask the question above.

Peregrines in temperate climates don’t begin incubating the eggs until the last or next-to-last egg is laid, though they do protect the eggs from cold, heat and rain.  The result is that all the eggs hatch within about 24 to 48 hours.  This makes the chicks approximately the same age and size as they grow up together.

Bald eagles, on the other hand, begin incubation immediately and the chicks hatch days apart.  The first chick is older and larger than the second, and so on.  The parents focus on feeding the largest chick who then becomes better able to compete for food.  The smallest chick often starves.  Sometimes the largest chick kills his siblings.

From what I have observed, peregrine nestlings are never aggressive toward their siblings, perhaps because they are all the same size.


March 17, 2008:  Over the weekend Tasha laid her 3rd egg so she will be incubating pretty much full time now.  See her progress on the National Aviary’s webcam

March 19, 2008:  We have confirmation today that Tasha has laid 4 eggs.  It’s likely her clutch is complete now.

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