Wet & Wild May: Osprey When it comes to big birds of prey, Duke Farms is world famous for the eagles the nest on the property. Many people who visit and see a large raptor for the first time are convinced they saw one of our resident eagles. Maybe they did in fact see our national symbol, but there are some other exciting possibilities that soar in the skies over the property. The most common sightings are of turkey vultures, black vultures and red-tailed hawks. If you are near the Great Falls, Vista Lake, or the Raritan River when you spot a big dark brown raptor with a 5 to 6 foot wingspan you may also be viewing the majestic osprey (Pandion haliaetus).
Ospreys have dark brown plumage on their backs, but their bellies and under wings are white. Females are typically larger than the males but they both have white heads which can be confused with eagles from afar. Unlike the eagle, the osprey has distinct dark bands of brown running through the eyes on the sides of their faces like a mask. They also have brown streaks above the beak and on the slight crest on the top of the head as well. The long narrow wings are also dark brown above with a lot of white on the underside. In flight the wings look like a stretched letter “m” which is a unique identifying feature for this raptor. Another sure way to know this bird is to listen for its unique call. Their high-pitched whistles and urgent repeated alarm calls sound ever so much like a whistling tea kettle.
Born to Fish The osprey truly earns its nickname fish hawk as its diet consist almost exclusively of fish. More than 80 species of fish account for about 99 percent of the osprey’s diet. And big fish too; their catch usually measures about half a foot to a foot in length and weigh anywhere from one-third to a pound. Research has shown that ospreys are successful in snagging a meal one in four tries, with success rates sometimes as high as 70 percent.
Part of their success is because ospreys have feet that are made for fishing. They have reversible outer toes that are capable of positioning themselves either at the front or the rear of the feet. This helps the bird seize prey with a pair of toes pointing to the front and another pair to the back. This combined with their elongated and twisted claws keeps struggling fish from getting away. The birds also have barbed pads on the soles of their feet and the spiky texture makes it much easier to grasp onto slippery fish. The tiny spikes are called spicules.
It is no surprise then that the osprey’s diet tells us everything about its habitat. Osprey can be found hunting in almost any shallow river, lake, reservoir, lagoon, swamp, and marsh with a plentiful supply of fish. Ospreys hang out in shallow waters as they are unable to dive to more than about three feet below the water's surface to catch their meals. Luckily, they don’t drown despite all the time spent hitting the water. Ospreys' nostrils have specialized valves that prevent water from making its way into their nasal
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cavities while they're fishing for dinner. Once ospreys hit the surface of the water, these valves immediately close.
Nesting and Breeding Ospreys make their nests out in the open, usually on an elevated perch free from predators such as raccoons. They also readily build nests on manmade structures such as telephone poles, channel markers, duck blinds and platforms erected just for them. Platforms began to be installed in wetlands by wildlife biologists when ospreys suffered calamitous population declines from the 1950’s to the early 70’s. Because of DDT interference with egg shell formation ospreys nearly went extinct over much of the U.S. After the ban of DDT in 1972 populations rebounded and grew by 2.5% per year from 1966 to 2015 according to the North American Breeding Bird Survey.
Ospreys build their nests with sticks and line them with bark, sod, grasses, algae, or human debris. The male usually collects most of the nesting materials and the female decides where to place it. The first season that a pair make their nest on an artificial platform it only measures about 2.5 feet in diameter and about 6 inches deep. But ospreys return to their nest year after year and eventually can end up with nests up to 6 feet in diameter and up to 10 feet deep!
Nesting ospreys aggressively defend the immediate area around their nest and chase away other ospreys that come too close. In breeding season, males perform a "sky-dance," or "fish-flight” to impress his mate. In this acrobatic display, the male swoops as high as 600 feet or more above the nest site all the while making screaming calls until he gradually descends back down to the nest.
Once mated the female lays between 2 to 4 eggs over several days. Both the male and female take turns incubating them for 36 to 42 days. Not all osprey eggs hatch at once and there can be a gap of up to 5 days between the time that the first and egg hatches and the last. This gives the oldest hatchling a huge advantage over his smaller siblings. If there is lots of food available then it doesn’t usually make a huge difference to the birds, but in scarce times the older one may get all the food and the younger ones may actually starve to death.
About 2 months after hatching, young osprey make their first flight. After fledging, the young remain with their parents for up to two more months, and then make their first migration south to their wintering grounds in Mexico and Central America alone. They remain at their wintering grounds for two to three years until they return north to make their first attempt at breeding.
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Although ospreys are a huge conservation success story, they are still listed as endangered or threatened in some states where pesticides eliminated total populations. Like the bald eagle, ospreys continue to increase their numbers but they face new threats of climate change and human behavior. With a bird of prey that depends solely on fish, the status of fish populations can make or break this bird. But with warming oceans, plastic pollution and overfishing, fish populations are being severely impacted. Every living organism on the planet is being impacted by too much carbon in the atmosphere, too much plastic waste in our waters, and not enough action to reverse the trend. We can only hope that this majestic bird that was brought back from the brink of extinction will continue to have a bright fishy future.
Additional Resources Osprey, All About Birds Osprey facts, fws.gov Barnegat Light osprey cam, conservewildlife.org Osprey, conservewildlife.org
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Activity: Whose Talons? Review bird feet adaptations and match the talons to determine the correct bird of prey.
A 1
B 2
C 3
Osprey 1: with matched is C
agle e Bald : B is matched with 3 with matched is B
wl o orned h Great : A is matched with 2 with matched is A
Answers to matching: matching: to Answers
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Additional Questions
What adaptations does this bird have that enables it to be particularly suited to an environment that includes water?
Plastic pollution is of great concern to our land and waterways. Using information included in the following Duke Farms resource, describe how the plastic problem may influence osprey populations.
If your friend reported to have seen an osprey at Duke Farms. What questions might you ask them to determine if it was indeed this bird of prey or another?
New Jersey Learning Standards Consider the following aspects of the NJ DOE Student Learning Standards when using this article in your formal or nonformal teaching and learning:
LS2.C: Ecosystem Dynamics, Functioning, and Resilience ♣ Moreover, anthropogenic changes (induced by human activity) in the environment—including habitat destruction, pollution, introduction of invasive species, overexploitation, and climate change—can disrupt an ecosystem and threaten the survival of some species. (HS-LS2-7)
LS4.B: Natural Selection ♣ Natural selection occurs only if there is both (1) variation in the genetic information between organisms in a population and (2) variation in the expression of that genetic information—that is, trait variation—that leads to differences in performance among individuals. (HS- LS4-2), (HS-LS4-3) ♣ The traits that positively affect survival are more likely to be reproduced, and thus are more common in the population. (HS-LS4-3) LS4.C: Adaptation ♣ Evolution is a consequence of the interaction of four factors: (1) the potential for a species to increase in number, (2) the genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for an environment’s limited supply of the resources that individuals need in order to survive and reproduce, and (4) the ensuing proliferation of those organisms that are better able to survive and reproduce in that environment. (HS-LS4-2) ♣ Natural selection leads to adaptation, that is, to a population dominated by organisms that are Patterns ♣ Different patterns may be observed at each of the scales at which a system is studied and can provide evidence for causality in explanations of phenomena. (HS-LS4-1), (HS- LS4-3) (HS-LS4-1) Natural selection leads to adaptation, that is, to a population dominated by organisms that are anatomically, behaviorally, and physiologically well suited to survive and reproduce in a specific environment. That is, the differential survival and reproduction of organisms in a population that have an advantageous heritable trait leads to an increase in the proportion of individuals in future generations that have the trait and to a decrease in the proportion of individuals that do not. (HS-LS4-3), (HS-LS4-4) ♣ Adaptation also means that the distribution of traits in a population can change when conditions change. (HS-LS4-3) ♣ Changes in the physical environment, whether naturally occurring or human induced, have thus contributed to the expansion of some species, the emergence of new distinct species as populations diverge under different conditions, and the decline–and sometimes the extinction–of some species. (HS-LS4-5), (HS-LS4-6) ♣ Species become extinct because they can no longer survive and reproduce in their altered environment. If members cannot adjust to change that is too fast or drastic, the opportunity for the species’ evolution is lost. (HS-LS4-5) Contact Kate Reilly, Manager of Education for more ideas and resources. [email protected].
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