Blog # 267 The Quiet Time Wanes

 Incubation—the quietest time in the osprey breeding season—is drawing to a close.  Sometime after Sunday, May 17, Ophelia’s eggs will start to hatch, about two days apart, in the order they were laid—that is if the eggs remain viable in this changeable,  unseasonably cold weather. 

Ophelia incubating eggs on her nest. Salt Point Osprey Nest Cam screenshot. 

Like other Osprey hens, Ophelia does the majority of the incubation, at least 60% of the daylight hours and throughout the night, and is spelled by her mate Orpheus so that she  can fly, eat, and perhaps bath. However, all ospreys have different temperaments and inclinations toward parenting. Some females are happy to get a break after sitting for hours while others almost refuse to leave their eggs except at meals. Some mated males never incubate the eggs and only guard them from afar, whereas other males will incubate for hours and only reluctantly leave the nest. Orpheus is in the latter group. 

A hungry Ophelia quickly relinquishes care of the eggs to Orpheus when he brings her a  fish, but is often reluctant to yield the eggs at other times. Orpheus and Ophelia can get 

Orpheus trying to shove Ophelia off her eggs. Salt Point Osprey Nest Cam screenshot. 

into scuffles to determine who will incubate, with the loser relegated to the perch to  preen. 

Ophelia lying flat on her eggs during a snow and hail squall. Salt Point Osprey Nest Cam screenshot.

On a stormy, freezing day like last Sunday, incubation is challenging. Ophelia laid low and very tight on her eggs as she and the nest were pelted with hail. Just one hit from a  hail stone could fatally crack an egg. Ophelia struggles in the cold, 28 mph gusts to shield the eggs while keeping her brood patch, a bare area of abdominal skin, in constant contact with her eggs. 

For proper development, Osprey eggs must be kept around 98.5 °F, which is a few degrees shy of Ophelia’s 104° F body temperature. Both parents have brood patches equipped with temperature receptors that sense egg temperature, enabling the gestating parent to regulate the time spent incubating more accurately. The growing embryo generates its own heat, to which the parents adjust by varying the length of time they directly sit on the eggs and the tightness or closeness of their bodies to the eggs.  At times, adult females may sit so tight on their eggs that the eggs appear to be missing from the nest.  

Ophelia rolling her three eggs. Salt Point Osprey Nest Cam screenshot. 

Both Ophelia and Orpheus roll and reposition the eggs periodically throughout the day presumably to warm the eggs evenly and to prevent embryonic membranes from sticking to the shell. The embryo inside the egg is sensitive to high temperatures and must be kept out of the sun. On warm days, adult females stand over their nests holding their wings slightly out to shade their precious eggs. Embryos are less sensitive to cold 

and can be left uncovered for nearly a half hour in warm weather without harm. They will perish, however, in cold and wet conditions. Humidity is important for shell development: too much can rot the egg while too little can make the shell too tough.  

This has been a cold, wet spring, which makes me a tad nervous, but the end is nigh.  Ophelia’s eggs should start hatching starting May 18-20. 

Eyes to the sky! 

Candace 

Candace E. Cornell  

Friends of Salt Point  

Lansing, NY 

ALL EYES ON OSPREYS 

WATCH! 

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