Good evening from the Eastern Shore! The wind is howling, the tide is incredibly high and the full moon is shining on the water. It is so bright that we can see Tom sitting on the dock, specifically on the boat lift. He has been spending the night somewhere around the dock, either on the perch that Crazy Osprey Man put up in the water just off the dock (more about the perchs to come), or on one of the pilings. Now it seems that the boat lift will be added to Tom’s available sleeping quarters. Audrey, of course, is snug and warm on her eggs in the nest.
In the next several days, we will try to take some photographs of Tom and Audrey’s digs. We all have a long wait for the eggs to hatch, usually about five weeks from the time they are laid. So our blogs may not be as frequent as they were during the hectic egg laying days. But we will continue to let you know what is going on, and this will be the time for some anecdotal stories about some of our osprey adventures over the past 18 years of observing our Tom and Audreys, pre-camera and post-camera.
In the meantime, here is the promised second email from Dr. Paul Spitzer, which was sent to us on April 9, 2013 as a follow-up to the email we posted a couple of days ago:
“The female is larger and heavier: Thus she guards the nest, makes the eggs, and has the mass to efficiently transfer heat during incubation and brooding. The pair’s cooperative buildup of the nest structure lets her hunker down in bad weather and at night, to conserve her energy while keeping eggs/nestlings warm. Currently (April 9) the nest is lined with fine grass, which suggests she will lay her first egg very soon. There was a piece of sky-blue plastic, which may now be buried in the nest lining. Ospreys often line their nest with a plastic bag, which suggests they have figured out the insulating and moisture-conserving value of sheet plastic. How did that happen?: Ospreys’ annual mortality rate is low, about 15%, and the survivor recruits a new mate. Thus all kinds of accumulated learning gets transferred to the newcomer: This is “Osprey Culture”, and the traditional annual nest site is the focus for this remarkable learning process.
Males are generally smaller in size than females, and they always weigh less (no overlap, based on a large sample I trapped years ago during my big Chesapeake osprey ecology study in the 1980’s). The weight difference, male weight averaging 80-85% of female weight, is greater than the size difference, resulting in the male’s much lighter wing loading. This enables him to be the commuter, radiating out to prime fishing sites and toting fish back to the female and young in an energetically efficient manner. During his hunt he gets wet, then shakes his well-oiled plumage when rising back into the air, but he is probably still too damp for a lot of egg incubation. I see males incubating late on mild mornings in May, when drying conditions are good, ambient temperatures are favorable, and the female is ready for a well-deserved break.
The female has stockier legs to support her greater mass. Some males’ legs look downright skinny, but of course they are very strong to withstand the impact with fish during the steep hunting dive, when four curved talons on each foot are driven into the unwitting fish.
At this nest the male has some buff feathers in his crest: A unique marker enabling easy ID. This can be seen in the still photograph above the cam. Male plumage is usually a shade darker, which does not show in that picture. This may be due partly to the copious oil with which he anoints himself during frequent bouts of preening, billing it from a wick on the large oil gland at the base of his tail.
Females are darker on the breast, ranging from a fine necklace of dark feathers (which this female has) to a full bib. Melanin pigments impart strength to feathers, so this may reduce wear during the female’s prolonged incubation duties and her breast contact with nest materials.
The photo clearly shows the subtle sexual difference in eye color. The eye of the female in the foreground is lemon yellow, and that of the male behind her is gold.
Finally, sexual size and role differences result in a zone defense at the nest: The more mobile male rises to chase Bald Eagles from the vicinity. Year-round resident eagles are potential predators of incubating females and young, but male ospreys police them out the area when they return from the tropics. This can result in spectacular chases on the rivers of the Chesapeake, where both species abound in spring. The aggressive scream of the male osprey will alert you to these events.
Oh yes!: I can’t forget the male’s spectacular courtship flights, in which he hovers and dives high above the nest while carrying a newly caught fish, calling all the while. The fish flashes in spring sunshine as the male becomes an aerial acrobat. Not surprisingly, mating often follows.
All of this is a remarkably fine-tuned and graceful evolutionary story, which the patient scientist reads in nature.”
Paul Randolph Spitzer, Ph.D.
Windy Hill on the Choptank River, MD
April 9, 2013
That’s it for tonight from beautiful Eastern Shore!
Crazy Osprey Man and Mrs. Crazy Osprey Man
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