Blog #389 What Goes in Comes Out

Female Osprey eating a fish, courtesy of Karel and Cynthia Sedlacek. 

Ospreys in Cayuga Lake are piscivores, consuming a diet of fish 99% of the time. The remaining 1%  represents an adult male nesting at Rivers Crossing Campground and Marina at Mays Point at the north  end of the lake. This male hunts fish and water snakes, flying with wriggling snakes in tow over the  dismayed campers. Ospreys nationwide, covering freshwater and saltwater habitats, eat over 80 species of fish, although most males take only a handful of species. Brown bullheads, yellow perch, and white  suckers are the mainstay of Cayuga’s Ospreys. 

The Osprey has many adaptations for fishing such as a sharp, hooked beak and powerful talons,  providing a strong grasp of their prey and the ability to easily tear flesh. The soles of Ospreys’ feet are  lined with spicules—barbed pads, providing additional traction to grip fish. The Osprey's talons are  capable of snapping shut within two hundredths (2/100) of a second. (This may be the result of a tactile  reflex rather than a voluntary one.) The talons of these ambitious hunters latch so powerfully onto their  prey that there are claims of Ospreys drowning as a result of capturing fish too heavy and powerful to be  able to lift out of the water. Claims of Ospreys drowning in this manner remain unverified.

Ospreys rarely drink water, courtesy of Cynthia Sedlacek. 

When a male catches a fish he usually takes it to a tree and eats the nutrient- and protein-rich head needed to sustain his frequent hunting forays. After he is finished, the male brings the remainder of the  fish to the nest for the female and chicks to eat. Ospreys get all the nutrition and water they need from the  fish they eat. Females especially are exposed to sunlight the entire day as they shield the eggs and  nestlings with their bodies. The females pant constantly to cool off on hot days. For additional relief,  adults sometimes bathe in the lake or slow-moving Salmon Creek and may take a rare drink.  

The digestive system of an Osprey, courtesy of Weebly.com.

Their short, thick, fleshy muscular non-extendable tongues are adapted to manipulate fish inside the  mouth and push it to the back of the mouth for swallowing. Food is not chewed; it has to be digested entirely in the stomach. 

The food passes from the mouth to an enlarged area of the esophagus known as a crop, which serves as  temporary storage. The crop has salivary glands that begin breaking up the food before it enters the  stomach. The food then passes to a two-part stomach, first the glandular portion called the proventriculus, and then it passes to the muscular half known as the gizzard or ventriculus. Pepsin and hydrochloric acid  are secreted in the proventriculus, beginning the process of chemical digestion. Indigestible materials are  retained in the proventriculus while the remaining digestion continues to the ventriculus. The indigestible parts include scales, bones, skin, and fins, among other things, and will be packed into a pellet and then  egested. Egestion is infrequent, and egested pellets are small, suggesting that much of the prey  consumed is digested and absorbed through the gut. 

Male Osprey coughing up a pellet consisting of indigestible materials, courtesy of Cynthia Sedlacek. 

Once the food is coated with highly acidic gastric fluids pH (1.7–2.0), it moves to the second stomach  chamber called the ventriculus or gizzard. This is where fish are “chewed” using sand and grain-like  particles to help mash the food. The muscular ventriculus contracts, mixing the food contents and  carrying out mechanical digestion. Because fish are readily digestible, the ventriculus is thin-walled and  poorly muscled in comparison to other birds needing more mechanical digestion. 

Partially digested food moves to the relatively narrow small intestine for further digestion and absorption.  For a carnivore, Ospreys have a comparatively longer small intestine with greater efficiency. The small  intestine is the site of further enzymatic digestion by enzymes produced in the pancreas such as  chymotrypsin, trypsin, and elastase break down proteins and fats in the small intestine. Nutrients are then  absorbed through the intestinal membranes and into the bloodstream. The Osprey’s large intestine is  reduced to a short, featureless connection between the small intestine and the cloaca where water  absorption occurs, before passing to the cloaca. The cloaca is the final holding area for the waste  products of digestion. 

Ospreys excrete metabolic waste products—mostly nitrogen— that are left over after food is broken down  for metabolism by the cells. Their droppings are white and high in uric acid. They simultaneously  evacuate uric acid and feces from an opening just under the tail that is called the cloacal vent. The  cloacal sphincter muscle can provide ejaculatory force, as demonstrated by the defecating Osprey in the 

photo below. There is no official measure, but Ospreys can squirt their fishy feces at least twelve feet so  watch out! Even day-old nestlings know to back up to the nest edge to relieve themselves. 

Osprey defecating at Myers Point. 

Humans excrete waste nitrogen as urea in urine which requires a great deal of water. Birds could not fly  with heavy water-filled bladders, and save their metabolic water reserves for other things such as long distance flights. Ospreys excrete nitrogen as uric acid in a concentrated form requiring no dilution. This  keeps the Osprey light and ready for flight. Uric acid excretion works well inside their eggs as well. The  metabolic waste produced by a developing shell-bound fetus can be neatly stored within the egg until  hatching. 

The Osprey's nutritious guano is beneficial to the land around their nests and favorite perching sites,  transferring nutrients and energy obtained from the lake ecosystem to the terrestrial ecosystem. This  guano fertilizes tree and vegetation growth, preventing erosion along our lakeshore and protecting  Cayuga’s water quality. 

Eyes to the sky! 

Candace 

Candace E. Cornell 

Friends of SaltPoint, Lansing, NY 

Cayuga Lake Osprey Network

GUEST PHOTOGRAPHERS: 

Cynthia Sedlacek captures exquisite shots of Cayuga Lake’s Osprey with her camera, which are frequently published in this blog. A tech wizard at Cornell and accomplished musician, Cindy gives us a  unique view of these spectacular raptors. Cindy is also an Osprey nest monitor for the Cayuga Lake  Osprey Network. 

EYESTOTHESKY! 

WATCH! 

Salt Point Osprey Nest Cam 

READ! 

OnOspreyTime: Ospreys of Salt Point 

VISIT! 

Cayuga Lake Osprey Trail 

HELP PROTECT OSPREYS: 

• Eggs will be hatching soon. Stay 300 feet away from nesting sites 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.