Blog #418 Pirates in the Sky—Avian Kleptoparasites

Bald Eagle attempting to pirate a fish from an Osprey at Potato Rapids Dam,

Marinette County, Wisconsin, courtesy of Buffalo Bill Center of the West.


Picture an Osprey, fish in tow, being pursued by a bald eagle twice its weight across the lake. The bald eagle is a well-known kleptoparasite (sometimes called a pirate), an animal that steals a meal from another animal (the host), and is a frequent stalker of Ospreys and other large birds carrying food. Kleptoparasitism is a common form of hunting, occurring in 197 species of birds and many forms of animals, from mollusks to mammals. 


Kleptoparasitism may involve birds of the same species (intraspecific) or between different species (interspecific.) The kleptoparasite gains either by obtaining prey or other objects that it could not obtain itself or by saving the time and effort required to obtain it, as in the case of the bald eagle. 


Birds with specialized feeding methods such as Ospreys and their spectacular dives are often the focus of kleptoparasitism since they attract much attention. After a successful dive, Ospreys fly with their catch dangling in full view. If a lurking eagle sees an Osprey with a fish in tow, the larger eagle will harass the Osprey until it drops the fish and the eagle takes it. Like the eagle, gulls can be interspecific kleptoparasites targeting Ospreys and other diving birds that bring their prey to the surface. Other famous kleptoparasites in the east include the golden eagle, Peregrine falcon, herons, American and fish crows, ravens, jays, and scrub-jays. Some species are especially aggressive kleptoparasites; gulls and herons are known to steal food from other birds and mammals. It is common for gulls to pilfer tidbits from restaurant dinner plates and steal food from beachgoers in coastal areas. 


Gulls and crows steal food from humans, courtesy of Flicker.


Young oystercatchers cannot crack open mussel shells to consume, but their parents can. To eat, the young become intraspecific kleptoparasites on non-parental adults. Other birds, including red-winged blackbirds and swallows, are inter- and intraspecific kleptoparasites, routinely stealing stones, twigs, and other nesting materials from members of their colony or other species.

As the post-fledging dependency period wanes, the young Ospreys incorporate kleptoparasitism into their role-playing. The photos below, taken by Cynthia Sedlacek, show an immature male chasing a young female after she caught a fish. He will pursue her until she drops her catch or gets away. The trick is knowing when the battle is won or lost and when it is time to give up and drop the fish. Since the male won’t eat a fallen fish, the evolutionary advantage of this play may be to teach each other how to evade other predators. The huntress kept her fish this time and is hopefully more prepared for the next one a bird tries to steal from her.





And she gets away with her fish!



Eyes to the sky!

Candace


Candace E. Cornell 

Friends of Salt Point, Lansing, NY

Cayuga Lake Osprey Network

cec222@gmail.com

  

Guest Photographer:

Cynthia Sedlacek, musician and Director of Data Administration and Reporting at Cornell University, is a surprising artistic talent. Cynthia’s affection and admiration for raptors are evident in her exciting photographs primarily of Ospreys nesting around Cayuga Lake and the red-tailed hawks of the Cornell Campus. Her photographs of local Ospreys are incomparable as she captures their essence, their jizz, and their inner bird. From the hard-to-see nestlings to the fast-flying adults, Cindy goes beyond the pale to catch all aspects of Osprey life in the Cayuga Basin. “My camera allows me to capture their beauty in many ways that the human eye can’t see,” she says, “like their spectacular wing positions and detailed feather patterns.” Cindy and her husband Karel are also avid nest monitors for the Cayuga Lake Osprey Network and video stream footage of the campus hawks.




EYES TO THE SKY!


WATCH!

Salt Point Osprey Nest Cam


READ!

On Osprey Time: Ospreys of the Finger Lakes


VISIT!

Cayuga Lake Osprey Trail



HELP PROTECT OSPREYS:

•Stay 300 feet away from nests during the breeding season. If the Osprey vocalizes, you are too close! Back off Immediately.

•Carry binoculars to view wildlife from afar.

•Help keep local waters clean, healthy, and safe.

•Recycle used fishing lines, twine, and nets, which can kill Osprey.

•Join the Cayuga Osprey Network and volunteer to help monitor Osprey nests: cec222@gmail.com.

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