Fascinating Aspects of Amphibian & Reptile Biology
MUD, ROOT BALLS, AND OTHER TASTY TIDBITS IN CROCODILIAN STOMACHS
In addition to normal prey items, the occurrence of plant material, wood, stones, man-made objects and mud in the stomachs of crocodilians is widely recorded in the literature (Brander 1925; Cott 1961; Delany and Abercrombie 1986; Delany, Woodward and Kochel 1988; Fitzgerald 1989; Fogarty and Albury 1967; Gorzula 1978; Hippel 1946; Hutton 1987; Magnusson, DaSilva and A.P. Lima 1987; McNease and Joanen 1977; Taylor 1979; Thorbjarnarson 1988, 1993; Tucker, Limpus, McCallum, and McDonald 1996; Valentine, Walther, McCartney and Ivy 1972).
Cott (1961) reported that most Nile crocodiles, Crocodylus niloticus, more than one year old had stones in their stomachs. He pointed out these stomach stones could be acquired (1) accidentally when grabbing prey, (2) indirectly from the stomachs of prey, and (3) by deliberately swallowing them. Accidental acquisition can be ruled out since most crocodiles in a population contain the same percentage body-weight of stones; older crocodilians do not contain a proportionally greater load of stones. Acquisition from the digestive tracts of prey also can be eliminated, since the prey of many Nile crocodile populations do not ingest stones, e.g., stones are found in young crocodiles that are feeding on invertebrates and amphibians, and adults that feed on pelicans, catfish, and talapia. Indirect support for the deliberate ingestion of stones comes from observation of crocodiles that live in stone-free swamp habitats with soft bottom ooze and travel long distances out of that habitat to find and devour the stones.
Cott (1961) also reviewed the suggested function of stones found in the stomach, e.g., digestive (gastrolith food grinding) function, filling (hunger appeasement) function, and hydrostatic (ballast) function.
While conducting surveys of the caimans of Bolivia,
we encountered two caimans, one in 1986 and one in 1995, with items in their
stomachs that are so unusual that accidental or inadvertent ingestion seems
to be the only reasonable explanation for their presence in the stomachs.
On 14 July 1986, four adult yacare caiman, Caiman yacare, were collected in the Río Zapacos west of Yaguaru, ca. 15°35' S, 63°14' W, Nuflo de Chavez Province, Santa Cruz Department, Bolivia. The limbs and tail of one of the specimens, UF 120019, appeared lean, but its belly was so grossly swollen that it appeared as though it were about to burst. After the specimen was euthanized, an incision was made in its abdomen to determine the cause of the swelling. The stomach was completely filled with black mud. Mixed in the mud were the remains of crocodilian eggshells, most probably Caiman, but possibly Melanosuchus or Paleosuchus. The mud was washed away and the eggshells retained.
Crocodilians are known to eat empty eggshells and embryonic membranes after the young have hatched (Kushlan and Simon 1981; McNease and Joanen 1977; Pooley 1977). When a clutch of eggs is developing in the oviducts of a female crocodilian, calcium is stripped from her body to lay down protective shells around the eggs and to add the mineral to the yolk that feeds the growing embryos while they are building skeletal tissue. Consuming the eggshells after eclosion both returns some calcium to the female and removes debris that might attract predators. Clutches of unhatched eggs may also be eaten by adults (Deitz 1979; Magnusson 1980; Whitaker and Whitaker 1976, 1984).
The digestive contractions of the stomach may have rolled those first roots into a ball, which provided a bolus around which later roots were wound resulting in the 20.3 cm (8 inch) diameter ball that was found. A ball that large could not be passed through the pelvic girdle or cloaca. Had the caiman not been killed, the ball might have grown to an even larger size.
The mud and stringy roots were too soft to serve a digestive
gastrolith function, and while the stomachs certainly were filled, it seems
unlikely that the two caimans would have swallowed these materials to serve
a hunger appeasement function. Sufficient mud was swallowed to have a hydrostatic
effect, but the weight of the roots was far too little. The most probable
explanation for how these materials got into the stomachs of these two caimans
is they were inadvertently ingested when the animal was swallowing a target
item.
LITERATURE CITED
F. Wayne King, Florida Museum of Natural History, Gainesville, FL 32611-7800, U.S.A., and Robert Godshalk, Department of Wildlife Ecology and Conservation, University of Florida, Gainesville, FL 32611-0430, U.S.A.
Suggested Citation: F. Wayne King and Robert Godshalk. 2003. Mud, Root Balls, and Other Tasty Tidbits in Crocodilian Stomachs. 6 p. [Online] Available at: http://www.flmnh.ufl.edu/natsci/herpetology/herpbiology/TidbitsinCrocDiet.htm
This document formatted by F. Wayne King.
Copyright ©
2003 Florida Museum of Natural History
The background for this page is derived from the flank scales of the yacare caiman, Caiman yacare.
Figure 2. Dante Videz-Roca holding the rootball recovered from the stomach of a Melanosuchus niger. F. Wayne King photo.
After the young had hatched, this female yacare caiman probably scavenged the empty eggshells and inadvertently picked up mouthfuls of mud along with the shells. Possibly the mud was saturated with embryonic fluids released when the hatchlings burst forth from the eggs. In any event, the quantity of mud she consumed not only blocked her stomach, but its mass also was sufficient to mechanically obstruct the rest of the digestive tract as well. Her gaunt condition suggests she would not have survived this ingestion event.
On 14 November 1995, we visited a large cattle ranch, El Ceilan (ca. 14°49' S, 65°10' W) located close to the Mamore river in Moxos Province, Beni Department. The ranch owner had recently killed a 2.5 meter (98.43 inches) long black caiman, Melanosuchus niger, in a nearby creek and was preparing the hide for vegetable tanning on-site using traditional methods (Figure 1).
He had examined the stomach contents and discovered a large fibrous ball. The ball was approximately 20.3 cm (8 inches) in diameter and composed entirely of roots (Figure 2 and Figure 3).
The fibrous mass had been removed from the stomach of the black caiman and had been dry for some time. Its estimated dry weight was about 1 kilo (2.2 lbs). The roots appeared to be similar to the roots of the aquatic plants, Hydrocotyle sp. or Eichhornia sp., several species of which are common in the area. The long creeping stems and circular leaves of Hydrocotyle often form dense mats along the shore and in the shallow marshy edges of waterways.
Similarly, the inflated leaves and stems of Eichhornia, with a diaphanous veil of roots hanging beneath them, form close-ranked floating mats on many of the local waterbodies. In all probability, the black caiman snapped up some fish, crustacean, or other prey species hiding in the midst of one of these vegetative mats and inadvertently swallowed some of the roots. The roots, which are filled with cellulose, are largely indigestible so they did not dissolve.
