Osprey Tales

The Eagle

Has been watching.

   “There’s something going on here, but I don’t know what it is.”

Ospreys transfer their heat via a temporarily bare area of abdominal skin called the brood patch.

Large birds of prey such as ospreys and eagles have small brood patches which corresponds to a longer incubation time.

Ospreys can sense their embryo’s movements and temperature with receptors in their brood patches. This helps them regulate their attentiveness (time spent incubating) more accurately. Since the embryo itself increasingly generates heat as it develops, periods of attentiveness can decline as incubation progresses.

“When you see me rocking back and forth on my eggs, I am positioning them into my brood patch.”

The eagle’s brood patch

The act of sitting on eggs to incubate them is called brooding.

For an osprey egg to develop normally, it must be exposed for a considerable length of time to temperatures a few degrees below the normal avian body temperature of 104 degrees. The incubation time of osprey eggs is 35 to 39 days.

Successful incubation requires a brood patch.

 A what?

Male provides female with all food during incubation. When the male brings in a fish, there is usually a” switch off”.

Female takes fish to nearby perch and feeds there; male incubates while female feeds, but sometimes will initiate incubation independent of food transfers.

Both sexes incubate. Females 80%, Males 20% –  during daylight hours.

Females nearly always incubates at night.

“Switching off”

 Incubation begins with the first egg, so the eggs hatch in sequence in 37-38 days. 

(Due date May 17 – 18)

 A three-egg clutch takes about 6-7 days to complete; a 4-egg clutch probably 8-10.  Looks like a two-egg clutch this year. But that is wonderful.

Two is company

Oh Wow! Two!

April 16, 2020

Osprey “clutch size” ranges from 2 to 4 eggs. Roughly 80% of North River females lay three. It is known from banding studies that a 2-egg clutch reflects a young female, a first-time breeder.  4-egg clutches are associated with food-rich nesting areas.

April 15, 2019

April 11, 2018