Turtles and Eagles

Moozillion

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I subscribe to an online periodical, "Nature Notes" by Dr. Bob Thomas from Loyola (New Orleans) Center for Environmental Communication. I don't know how to attach things in emails, so I'll just re-type the brief article here.

"One thing we know about natural history is that we don't know everything and there are always new discoveries. Steve Shively, a wildlife biologist with the Calcasieu (pronounced KALL-kuh-shoo...Moozillion) Ranger District of the U.S. Forestry Service, was tasked with an ominous job July 24, 2013. He has experience climbing trees to work on red-cockaded woodpeckers, so it seemed logical for someone to assign him the job of climbing 100 feet up a loblolly pine tree near Kincaid Lake, Rapides Parish/County, to the nest of a Bald Eagle. The real challenge in climbing such heights to an eagle's nest is when one gets to the top of the tree under the nest- the next step is to cling to the underside of the nest, leaving the "safety" of the tree trunk, and slowly inching around to the surface of the nest. Not the job for just anyone!!!

Well, Steve was successful. What an exhilarating experience for a seasoned naturalist. He was sitting on top of the world in the wide-open sky, with an active Bald Eagle nest in front of him. He said he stayed in one quadrant of the nest- didn't move around- but what he saw was not anticipated.

Obviously, eagles bring food to the nest, especially when young are present. Although not part of Steve's mission, he made informal observations on the remains of the food items the birds brought to the nest. Although fish remains are expected, the only one Steve found was a flathead catfish skull, from a fish estimated at 2 feet in length. No mammal remains were obvious, but there was an earlier report at this nest that an eagle brought a cat (with a collar) to the nest, and a biologist later found cat mandibles on the ground below.

Steve's surprise was the number of turtle remains, and the species he found. There were only three species that he could see: razor-backed musk (Sternotherus carinatus), small false (Mississippi) map turtles (Graptemys pseudogeographica) and softshell turtles (Apalone sp.- the largest having a carapace of 8 inches). He saw hundreds of turtle pieces-parts, with their abundance in the order they are listed above. The surprise was that there were no remains of the most common turtles in Kincaid Lake: red eared sliders (Trachemys scripta elegans) and river cooters (Pseudemys concinna). He did find a number of turtle shells on the ground that had fallen from the nest.

There may be a simple reason for the dominance of the 3 species found. The softshells are obvious: the eagles' talons can pierce the soft tissue covering the skeleton. The two species with hard shells share features that might make them more easily grabbed than other species on the surface of the water. The razor-backed musk is basically triangular in cross-section due to the sharp keel down the back and the angled lateral margins around the edges of the carapace. The map turtle has a series of enlarged knobs down the center of the carapace, creating the same effect. These features make it very easy for the eagle talons to gain purchase on an otherwise hard, somewhat slick shell by wrapping around 2 of the 3 angled regions.

Steve thinks razor-backed musks may be chosen due to having easy access to their flesh since they have a relatively small plastron. Red-eared sliders and river cooters are mostly rounded, and it would be harder (not impossible) for the bird to grab them and hold on. Jeff Boundy, herpetologist with the Louisiana Department of Wildlife and Fisheries (note: and a very nice, accessible, knowledgable guy!- Moozillion) says that razor-backed musk turtles feed at certain, predictable times of day in shallow, often clear water. When doing so, they are oblivious to what is going on around them and may make easy targets for eagles that recognize them and their habits as a food source. They and map turtles often sun on logs above the water, and this may make them both easy targets. Softshell turtles do the same, but also often rest in shallow waters and are probably vulnerable to predation. Of course, the latter may not be as tasty as the former!

Steve also found a single western ratsnake (Pantherophis obsoletus) egg in the nest. It appeared viable and had no fungal growth. Ratsnakes are characteristically active in crowns of trees and it is not surprising that one living in and around an eagle nest might lay its eggs there. I would think, however, that a baby ratsnake, at about 7 inches in length, would be at a disadvantage sharing the platform with keen-eyed, voracious baby eagles!"
 

Maverick

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Interesting, thanks for taking the time to retype and post it here.
 

Pokeymeg

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Very interesting! Sad to think about turtles being eaten :( but that is just nature, of course!
 

wellington

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The size is what would concern me if I had lots of eagles in my area. 8 inches. That's not too much smaller then my leopard. I know they would go for a tortoise, but wonder if a tortoise, being on land and the way of their shape would be hard for them. Interesting, thanks for sharing.
 
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