April 27, 2006
Predators
Technical Note: I wanted to mention a quick technical note. One of our cam watchers asked why the Osprey Cam is not in color like the Eagle Cam. The Osprey Cam is a color camera, but when it is cloudy, it is hard to see the colors. Also the area behind the ospreys is rather brown at this time, so the colors on the cam image are rather muted. But the camera we're using is a color camera.
And while I'm talking about the camera, I'll mention another topic: Personally I've noticed that our infrared image at night is a bit washed out. We believe that this is due to the age of our camera, and we plan to install a new cam after the osprey family migrates south in September.
Nest Update: The osprey parents seem to be falling into a nice rhythm these days. The mother sits on the eggs the majority of the time (probably around 70%) and the father comes in occasionally to bring her a fish and to relieve her for a while so she can take a break.
Both parents also roll the eggs (about once an hour) to make sure they are evenly heated and to ensure that the embryos do not stick to the inside of the eggshells. The warmth that the parents provide is crucial to the proper and timely development of the small chick inside each shell.
During our big rain last weekend, we saw the female really wedging herself down into the nest cup and keeping a wall of nesting material around her to keep all the eggs safe and warm. Here you can see a photo comparison of the parent's sitting position from last year when compared to our parent last weekend during the heavy rains.
The parents have quite a challenge in keeping four eggs near their brood patch, which is the featherless area on their stomachs that they press against the eggs to keep them warm.
Every so often, we also see the parents looking up and calling out to something in the sky over them. Threats to an osprey nest depend on where it is located. A land nest is vulnerable to raccoons, skunks and foxes, which is why most ospreys that are nesting on land like to be very high in the air -- like our ospreys on the cam platform. When the osprey nest is high, the main threat will then come from the air.
What could threaten the ospreys and their eggs? Possibly a single male or female osprey that has not found a nest or a mate, and is looking for a bit of trouble. In addition, sometimes bald eagles will fly too close to an osprey nest, making the osprey parents aggitated. If the parents left the eggs completely unattended, then crows, ravens, and jays would surely pay the nest a visit. But one of the greatest threats at this stage would be from a Great horned owl -- also called the "winged tiger" (click on the thumbnails below):
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According to osprey expert Alan Poole, the nocturnal Great horned owl is one of the only species known to take out an adult osprey sitting on a nest. During Poole's experiences with ospreys he has found dead incubating females that possessed talon marks much like those of a Great horned owl.
Fortunately, these attacks on the adult are rare. It is more likely that the owl would try to take the eggs or the chicks. This same threat would have also applied to the bald eaglets when they were younger -- and that is why we would see the mother eagle keeping watch over the chicks at night on the Eagle Cam.
Great horned owls are found throughout Maryland, and last year after the ospreys had migrated, we were treated to the sight of one on the osprey platform at night.
Despite their formidable reputation and appearance, Great horned owls are beautiful and amazing creatures that perform very useful and important services in our environment. Great horned owls are vital to controlling populations of small and medium-sized mammals, and they actively help farms and local gardens naturally manage their rodent populations without the use of traps or rodenticides. The owls' role in rodent control is also why many people buy those plastic owls from the garden store and place them on their property, because just the threat of an owl is sometimes useful in keeping away the rodents.
In Maryland forests, Great horned owls mostly take rabbits, but also snakes, mice, skunks, ground squirrels, Norway rats, wood rats, and muskrats. Sometimes their diet will also include toads, lizards, frogs, turtles, coots, geese, herons, and avian chicks. Biologists report that despite this varied diet, nine out of ten times the owl's prey will be a mammal.
The Xcel Energy website has an active Great Horned Owl Cam that is interesting to watch. At this time, they also have several photos posted that show the hatching of this season's two chicks -- or owlets.
You can learn more about Great horned owls by reading their informative Life of a Great Horned Owl fact sheet (a PDF file).
Until next time,
Lisa - webmaster
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