Dietary biology of the Nile crocodile

Add links
Source: Wikipedia, the free encyclopedia.
Masai Mara

ectothermic metabolism, so can survive for long periods between meals—though when they do eat, they can eat up to half their body weight at a time. However, for such large animals, their stomachs are relatively small, not much larger than a basketball in an average-sized adult, so as a rule, they are anything but voracious eaters.[3]

Young crocodiles feed more actively than their elders according to studies in Uganda and Zambia. In general, at the smallest sizes (0.3–1 m (1 ft 0 in – 3 ft 3 in)), Nile crocodiles were most likely to have full stomachs (17.4% full per Cott); adults at 3–4 m (9 ft 10 in – 13 ft 1 in) in length were most likely to have empty stomachs (20.2%). In the largest size range studied by Cott, 4–5 m (13 ft 1 in – 16 ft 5 in), they were the second most likely to either have full stomachs (10%) or empty stomachs (20%).[4] Other studies have also shown a large number of adult Nile crocodiles with empty stomachs. For example, in Lake Turkana, Kenya, 48.4% of crocodiles had empty stomachs.[5] The stomachs of brooding females are always empty, meaning that they can survive several months without food.[2]

Invertebrates

The type and size of the prey depends mostly on the size of the crocodile.

dragonflies. Arachnids such as Dolomedes water spiders are taken, but always secondarily to insects in Uganda and Zambia.[4][7]

Mollusks may occasionally be taken by young crocodiles (they are taken in larger numbers later in life in parts of Uganda and Zambia).[4] In the Okavango Delta, Botswana, the diet was similar but young crocodiles ate a broader range of insects and invertebrates, with beetles taken in similar numbers to other, similar prey, both aquatic and terrestrial. In Botswana, arachnids were more often found in young crocodiles than in Uganda and Zambia.[7] In Zimbabwe, the dietary composition was broadly similar to that in other areas.[6] However, in the Ugandan portion of Lake Victoria, true bugs and dragonflies both seem to outnumber beetles notably and up to a length of 1 to 2 m (3 ft 3 in to 6 ft 7 in) crocodiles had stomach contents that were made up 70–75% of insects.[8][9]

After Nile crocodiles reach 2 m (6 ft 7 in), the significance of most invertebrates in the diet decreases precipitously.[4][7] An exception to this is in Uganda and Zambia, where subadults and adults of even large sizes, up to 3.84 m (12 ft 7 in), may eat very large numbers of snails. Nearly 70% of the crocodiles examined by Cott (1961) had some remains of snails inside their stomachs. Predation on amuplariid water snails was especially heavy in Bangweulu Swamp, Lake Mweru Wantipa, and the Kafue Flats, where mollusks representing 89.1, 87, and 84.7% of all prey in these locations, respectively. Gastropoda (4126 records per Cott) were taken much more than Lamellibranchiata (six records). Notable favorites include Pila ovata, which lives just under water on rocky surfaces (mainly found in crocodiles from Uganda) and Lanistes ovum, which is found submerged among water plants and on detritus (mainly from stomachs in Zambia).[4]

Fish

Subadult with tilapia as its prey

During the time from when they are roughly 1.5 to 2.2 m (4 ft 11 in to 7 ft 3 in) long (roughly 5 to 9 years old), Nile crocodiles seem to have the broadest diet of any age range. They take more or less much the same small prey as smaller crocodiles, including insects and arachnids, but also take many small to medium-sized vertebrates and quickly become capable taking down prey up to their own weight. Fish become especially significant around this age and size. However, Cott (1961) found that the only size range where fish were numerically dominant over other types of food was from 2 to 3.05 m (6 ft 7 in to 10 ft 0 in). This size range consists of subadult males and a mixture of subadult and adult females.

striped mullet (Mugil cephalus) as they make their seaward migration for spawning. Here, the crocodiles may line up in dozens across narrow straits of the estuary to effectively force the mullet into easy striking distance, with no observed in-fighting among these crocodile feeding congregations. At this time of plenty (before irrigation operations by humans led St. Lucia to have dangerously high saline levels), a 2.5 m (8 ft 2 in) crocodile could expect to eat 1.1 kg (2.4 lb) of mullet daily, an exceptionally large daily amount for a crocodile.[12]

Larger fish, like catfish and freshwater bass, are preferred by adults more than 2.2 m (7 ft 3 in) in length. Particularly small fish are likely to be eaten only in case of sudden encounter, mostly in shallow, dry-season ponds where not much effort is needed to catch the small, agile prey.[13] Most observed fishing by crocodiles takes place in waters less than 1.5 m (4 ft 11 in) deep and fish are often caught when they swim into contact with the crocodile's head, even literally right into the reptile's mouth.[5] Across much of their range, they take any fish they encounter, but largish and relatively sluggish mesopredator fish such as lungfish and Barbus carp seem to be most widely reported. Many other genera are taken widely and relatively regularly, including Tilapia (which was the most significant prey genus in Lake Turkana), Clarias, Haplochromis, and Mormyrus.[4][5][14] In Uganda and Zambia, lungfish comprised nearly two-thirds of the piscivorian diet for crocodiles.[4] Similarly, in Lake Baringo, the lungfish is the crocodile's main prey and the crocodile is the lungfish's primary predator.[15] In the Okavango Delta, the African pikes (Hepsetus spp.) were the leading prey group for subadults, comprising more than a fourth of the diet.[16] Extremely large fish, such as Nile perch (Lates niloticus), goliath tigerfish (Hydrocynus goliath), and even sharks, are taken on occasion, in addition to big catfish, such as Bagrus spp. and Clarias gariepinus, which are preyed upon quite regularly in areas where they are common. In the Zambezi River and Lake St. Lucia, Nile crocodiles have been known to prey on bull sharks (Carcharhinus leucas) and sand tiger sharks (Carcharias taurus).[17][18][19] The largest fishes attacked in such cases may potentially weigh more than 45 kg (99 lb).[20][21]

When capturing large fish, they often drag the fish onto shore and swing their heads around to smash the fish onto the ground until it is dead or incapacitated. More modestly sized fish are generally swallowed whole.[5] The Nile crocodile has a reputation as a voracious and destructive feeder on freshwater fish, many of which are essential to the livelihoods of local fisherman and the industry of sport fishing. However, this is very much an unearned reputation. As cold-blooded creatures, Nile crocodiles need to eat far less compared to an equivalent-weighted warm-blooded animal. The crocodile of 2 to 3.05 m (6 ft 7 in to 10 ft 0 in) consumes an average 286 g (10.1 oz) of fish per day. In comparison, piscivorous water birds from Africa eat far more per day despite being a fraction of the body size of a crocodile; for example, a cormorant eats up to 1.4 kg (3.1 lb) per day (about 70% of its own body weight), while a pelican consumes up to 3.1 kg (6.8 lb) per day (about 35% of its own weight).[4][2] The taking of commercially important fish, such as Tilapia, has been mentioned as a source of conflict between humans and crocodiles, and used as justification for crocodile-culling operations; however, even a primarily piscivorous crocodile needs relatively so little fish that it cannot deplete fish populations on its own without other (often anthropogenic) influences.[22] Additionally, crocodiles readily take dead or dying fish given the opportunity, thus are likely to incidentally improve the health of some fish species' populations as this lessens their exposure to diseases and infection.[2]

Reptiles and amphibians

Captive adult Nile crocodiles feeding

reed frog (Hyperolius viridiflavus).[4][7] Even the largest frog in the world, the goliath frog (Conraua goliath), has reportedly been preyed on by young Nile crocodiles.[23]

In general,

turtles, were almost negligible in crocodiles under 2.5 m (8 ft 2 in) and most common in the stomachs of crocodiles over 3.5 m (11 ft 6 in) in length from Uganda and Zambia. Small species of reptiles are largely ignored as prey at this size. Freshwater turtles are often the most frequently recorded reptilian prey, unsurprisingly perhaps because most other reptiles other than a small handful of Lycodonomorphus water snakes are more terrestrial than water-based.[4]

In a study, the

puff adder (Bitis arietans), the forest cobra (Naja melanoleuca), and the black mamba (Dendroaspis polylepis) have been recorded as Nile crocodile prey.[4][2] The only frequently recorded lizard prey is the large Nile monitor (Varanus niloticus), although this mesopredator may be eaten fairly regularly, as they often share similar habitat preferences, whenever a crocodile is able to ambush the stealthy monitor, which is more agile on land than the bulkier crocodile.[4][2]

Birds

Pelicans have little to fear from crocodiles on land, but they can be vulnerable while swimming to crocodiles lurking under water.

Numerous birds, including

geese and ducks in Africa. Slow-swimming pelicans are also vulnerable to crocodiles.[30] Nile crocodiles apparently frequently station themselves underneath breeding colonies of darters, cormorants, herons, egrets, and stork and presumably snatch up fledgling birds as they drop to the water before they can competently escape the saurian, as has been recorded with several other crocodilians.[4][2]

Wading birds, even large and relatively slow-moving types such as the

spur-winged geese (Plectropterus gambensis) recorded as being taken largely while flightless due to molting their flight feathers.[31][32][33][34][35] In one case, a crocodile was filmed capturing a striated heron (Butorides striata) in mid-flight.[36] Ospreys (Pandion haliaetus) are known to be grabbed while they dive for fish[37] as are possibly African fish eagles (Haliaeetus vocifer), while crowned eagles (Stephanoaetus coronatus) have reportedly been ambushed on land at carrion.[2][38] Crocodiles are occasionally successful in grabbing passerines such as weaver birds, including the abundant red-billed quelea (Quelea quelea), and swallows, having been observed to breach the water and in a matter of seconds sweep off a branch full of birds with remarkable success.[2][39][40][41] Larger land birds, such as bustards, guineafowl, ground hornbills (Bucorvus spp.) and ostriches (Struthio camelus), may be taken when they come to water to drink, but like most birds, are seldom harassed and a minor part of the diet.[2]

Mammals

Determining the percentage of any specific food item in a crocodile's diet is difficult because their defecation in water makes scat analysis impossible, and capturing individual animals to analyze their stomach contents is painstaking. In addition, as an animal that feeds rarely, sometimes only a few times in a year, even the individual stomach content examinations sometimes prove to be unsuccessful. However, as crocodiles grow, relying solely on small and agile food items such as fish becomes difficult, this causes a shift in the diet as the animal matures, for energy conservation purposes, as in other predators.[4][5] Nonetheless, starting around 1.5 m (4 ft 11 in), they can become capable mammalian hunters and their ability to overpower a wide range of mammals increases along with their size. Crocodiles less than 3 m (9 ft 10 in) may take a variety of medium–sized mammals up to equal their own mass, including various monkeys, duikers,[42] rodents, hares, pangolins,[4] bats, dik-dik, suni (Neotragus moschatus),[43] oribi (Ourebia ourebi)[44] and other small ungulates up to the size of a Thomson's gazelle (Eudorcas thomsonii).[10]

Rodents and

water mongoose (Atilax paludinosus),[4] African wildcats (Felis lybica)[4] and servals (Leptailurus serval).[48]

Adult Nile crocodiles, i.e. at least 3.05 m (10 ft 0 in), are apex predators. While adults can and will consume nearly all types of prey consumed by the younger specimens, as adult crocodiles gain bulk, they lose much of the necessary maneuverability to capture agile prey such as fish and are not likely to meet their dietary needs by consuming small prey and may expel unnecessary amounts of energy, so take them secondarily to larger prey.

gorillas (Gorilla beringei) are thought to consider Nile crocodiles a serious threat.[51] Few details are known about the dietary habits of Nile crocodiles living in Madagascar, although they are considered potential predators of several lemur species.[52][53] Other nonungulate prey known to be attacked by Nile crocodiles includes aardvarks (Orycteropus afer)[54] and African manatees (Trichechus senegalensis).[55]

Wildebeest crossing the Mara River, attacked by crocodiles

Among the mammals, the bulk of the prey for adults are

bushbuck (Tragelaphus scriptus),[24] sitatunga (Tragelaphus spekii),[2] kudu (Tragelaphus strepsiceros),[57] steenbok (Raphicerus campestris),[58] eland (Taurotragus oryx),[46] gemsbok (Oryx gazella),[59] sable (Hippotragus niger) and roan antelopes (Hippotragus equinus),[59] up to a half dozen types of duiker,[43] topi (Damaliscus lunatus),[60] hartebeest (Alcelaphus buselaphus)[2] and both species of wildebeest (Connochaetes sp.).[61]

Other ungulates are taken by Nile crocodile more or less opportunistically. These may include

dromedary camels (Camelus dromedarius)[66] and cattle (Bos taurus)[67] In Tanzania, up to 54 head of cattle may be lost to crocodiles annually, increasing the human-crocodile conflict level. Goats (Capra hircus), donkeys (Equus asinus) and dogs (Canis familiaris) may also rank among the most regularly recorded domesticated animals to be taken by Nile crocodiles.[2][68]

Particularly large adults, on occasion, take on even larger prey, such as giraffe (Giraffa sp.),

Cape buffalo (Syncerus caffer),[24][69] and young African bush elephants (Loxodonta africana).[70][71] Even heavier prey, such as black rhinoceros (Diceros bicornis), have been killed by crocodiles. In one case in the Tana River of Kenya, as observed by Max Fleishmann (communicated via letter to Theodore Roosevelt), a Nile crocodile was able to bring down one of these huge herbivores by the help of muddy bank terrain, the adult female rhino's poor decision to enter deeper water rather than retreat to land and finally having been joined in drowning the animal by one to two other crocodiles.[2][72] An additional case of predation on an adult black rhino was reportedly observed in northern Zambia.[2] A bull giraffe that lost his footing on a river bank in Kruger National Park was seen to be killed by a large crocodile, while in another case there, a healthy bull buffalo was seen to be overpowered and killed by an average-sized adult male crocodile measuring 4.25 m (13 ft 11 in) after a massive struggle, an incident less commonly seen at this size.[5][24] Since crocodiles are solitary hunters, the Nile crocodile is the only predator in Africa known to attack full-grown Cape buffaloes alone, compared to the preferred pride attack method of lions.[73]

Although Nile crocodiles occasionally prey on

hippo calves, even large adult crocodiles rarely attack them because of the aggressive defense by mother hippos and the close protection of the herd, which pose a serious threat. Hippo calves have been observed to at times act brazenly around crocodiles, foraging without apparent concern and even bumping into the reptiles.[2] However, some large Nile crocodiles have been recorded as predators of subadult hippos; anecdotally, the infamous giant crocodile Gustave was reported to have been seen killing adult female hippos.[46][24][74] A 5 m (16 ft 5 in) specimen from Zambia was found to have eaten a "half-grown hippo".[4] At the no-longer-existent Ripon Falls in Uganda, one adult bull hippo was seen to be badly injured in a mating battle with a rival bull hippo, and was then subsequently attacked by several crocodiles, causing it to retreat to a reedbed. When the male hippo returned to the water, it was drowned and killed by the group of Nile crocodiles amid "a truly terrifying commotion".[2] However, other than rare instances, adults of megafauna
species such as hippopotamuses, rhinoceroses, and elephants are not regular prey and are not typically attacked, with the exception of giraffes, since their anatomy makes them vulnerable to attack while taking a drink.

Nile crocodiles occasionally prey on

jackals,[46][24] and cheetahs (Acinonyx jubatus).[10]

Vegetation

In the Nile crocodile as well as in at least 13 other species of crocodilian, a variety of fruit (mostly fleshy) has been found in stomach content. While these are probably sometimes used as gastroliths, they are likely often ingested for their nutritional value. Based on these findings, it has also been suggested that crocodiles may act as seed dispersers.[77]

References

  1. ^ "Nile Crocodile: Photos, Video, E-card, Map – National Geographic Kids". Kids.nationalgeographic.com. 17 October 2002. Archived from the original on May 7, 2007. Retrieved 16 March 2010.
  2. ^
    ISBN 978-0-7153-5272-4
    .
  3. ^ Huchzermeyer, F. (2003). Crocodiles: Biology, Husbandry, Diseases. CABI International Publishing. UK and Massachusetts.
  4. ^
    doi:10.1111/j.1096-3642.1961.tb00220.x
    .
  5. ^ a b c d e f g Graham, A. D. (1968). The Lake Rudolf Crocodile (Crocodylus niloticus Laurenti) Population. Masters of Science Thesis, The University of East Africa.
  6. ^
    JSTOR 4797
    .
  7. ^
    S2CID 46987629
    .
  8. doi:10.1111/j.1469-7998.1960.tb05579.x
    .
  9. doi:10.1111/j.1365-3032.1959.tb00223.x
    .
  10. ^ a b c Graham, A., & Beard, P. (1973). Eyelids of Morning. A. & W. Visual Library, Greenwich, CT, 113.
  11. ^ Hippel, E. V. (1946). "Stomach contents of crocodiles". The Uganda Journal. 10: 148–149.
  12. JSTOR 1443412
    .
  13. ^ a b Stevenson-Hamilton, J. (1954). Wild life in South Africa. Cassell and Co., London.
  14. ^ Cott, H. B. (1954). "The status of the Nile crocodile in Uganda". Uganda Journal. 18 (1): 1–13.
  15. doi:10.1111/j.1365-2028.2004.00536.x
    .
  16. ^ Wallace, K. M. (2006). The feeding ecology of yearling, juvenile and sub-adult Nile crocodiles, Crocodylus niloticus, in the Okavango Delta, Botswana. Doctoral dissertation. University of Stellenbosch.
  17. ^ "FLMNH Ichthyology Department: Bull Shark". www.flmnh.ufl.edu. Retrieved 23 October 2015.
  18. ISBN 9781107354999
    .
  19. ^ "Deadly bull shark is a magnificent, hunted creature | Florida Weekly". charlotte.floridaweekly.com. Retrieved 23 October 2015.
  20. ^ Pienaar, U. (1968). The Freshwater Fishes of the Kruger National Park. Republic of South Africa: The National Parks Board of Trustees of the Republic of South Africa.
  21. ^ Skelton, P. (1993). A Complete Guide to the Freshwater Fishes of Southern Africa. Halfway House: Southern Book Publishers Ltd.
  22. JSTOR 1941051
    .
  23. ^ Thomson, G. (2006). Goliath Frog (Conraua goliath). B Freedman, ed. Encyclopedia of Endangered Species, Vol. 1.
  24. ^
    doi:10.4102/koedoe.v12i1.753
    .
  25. doi:10.1046/j.0141-6707.2001.00328.x
    .
  26. S2CID 17057901
    .
  27. ^ Alderton, D. (1998). Crocodiles & alligators of the world. Cassell Illustrated, 978-0713723823.
  28. ISBN 0-231-11870-8
    pp. 137–159.
  29. PMID 1257732
    .
  30. ISBN 978-0816021741
    .
  31. ^ McKinney, F.; Buitron, D. & Derrickson, S. R. (1990). "Persistent quacking in dabbling ducks: a predator-luring signal?". Wildfowl. 41 (41): 92–98.
  32. ^ Pitman, C. C. (1965). "The nesting and some other habits of Alopochen, Nettapus, Plectropterus and Sarkidiornis". Wildfowl. 16 (16): 7.
  33. JSTOR 4085837
    .
  34. JSTOR 4089428
    .
  35. ISBN 0-934797-11-0
    .
  36. ^ "Crocodile snaps heron from air". YouTube.com. Retrieved 1 January 2015.
  37. ^ Poole, Alan F., Rob O. Bierregaard and Mark S. Martell. (2002). Osprey (Pandion haliaetus). The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology.
  38. ^ Simon Thomsett (6 June 2011). "Simon Thomsett on the African Crowned Eagle". African Raptors. Retrieved 1 January 2015.
  39. doi:10.1111/j.1474-919X.1954.tb02342.x
    .
  40. ^ Thiollay, J. M. (1989). Natural predation on quelea. Quelea quelea. Africa's Bird Pest 216–229.
  41. ^ Baker, S. W. (1891). Wild beasts and their ways: reminiscences of Europe, Asia, Africa and America. Macmillan and co.
  42. ^ a b c Kingdon, J.; Happold, D.; Butynski, T.; Hoffmann, M.; Happold, M. & Kalina, J. (2013). Mammals of Africa. Vol. 1. A&C Black.
  43. ^ a b Schütze, H. (2002). Field Guide to the Mammals of the Kruger National Park. Struik.
  44. ^ Tekalign, W. & Bekele, A. (2011). "Population Status, Foraging and Diurnal Activity Patterns of Oribi (Ourebia ourebi) in Senkele Swayne's Hartebeest Sanctuary, Ethiopia". SINET: Ethiopian Journal of Science. 34 (1): 29–38.
  45. ^ Fonck, H. (1910). Deutsch-Ost-Afrika: eine Schilderung deutscher Tropen nach 10 Wanderjahren. Vossische. Berlin.
  46. ^ a b c d e f Grenard, S. (1991). Handbook of alligators and crocodiles. Malabar, FL: Krieger.
  47. S2CID 198968982. Archived from the original
    (PDF) on 2015-09-19. Retrieved 2021-12-19.
  48. S2CID 84461675
    .
  49. S2CID 17070708
    .
  50. doi:10.1111/j.1469-7998.1966.tb04054.x
    .
  51. S2CID 1759228
    .
  52. ^ Small, E. (2013). Steven M. Goodman', Sheila O'Connor, and Olivier Langrand Field Museum of Natural History. Lemur Social Systems and Their Ecological Basis, 51.
  53. ^ Goodman, S. M., O'Connor, S., & Langrand, O. (1993). "A review of predation on lemurs: implications for the evolution of social behavior in small, nocturnal primates", pp. 51–66 in Lemur social systems and their ecological basis. Springer US.
  54. ^ Knöthig, J. (2005). Biology of the Aardvark (Orycteropus afer) Archived 14 April 2008 at the Wayback Machine. Ruprecht-Karls-Universität, Heidelberg, Germany (MSc thesis).
  55. ^ Dodman, T., Dagou Diop, N.M. & Khady, S. (eds.). (2008). Conservation Strategy for the West African Manatee. UNEP, Nairobi, Kenya andWetlands International Africa, Dakar, Senegal.
  56. doi:10.1111/j.1365-2028.1982.tb00279.x
    .
  57. doi:10.4102/koedoe.v45i1.12
    .
  58. ^ Schaller, G. B. (2009). The Serengeti lion: a study of predator-prey relations. University of Chicago Press.
  59. ^ a b "Nile Crocodile". Crocodiles of the World, Crocodile Conversation and Education Centre. Retrieved 1 January 2015.
  60. ^ Anthony, S. B. (2011). The feed and feeding Habits of Tiang (Damaliscus korrigrum) in the Sudd Region–Sudan (Doctoral dissertation, Sudan University of Science and Technology).
  61. ^ a b Mills, M. G. L. & Biggs, H. C. (1993). "Prey apportionment and related ecological relationships between large carnivores in Kruger National Park". Symposia of the Zoological Society of London. 65: 253–268.
  62. ^ Moehlman, P. D. R. (2002). Equids: zebras, asses, and horses: status survey and conservation action plan. IUCN.
  63. ^ Marshall Cavendish Corporation, 2004. Encyclopedia of the Aquatic World. New York: Marshall Cavendish.
  64. ^ Eltringham, S. K. (1999). The hippos: natural history and conservation. Princeton University Press.
  65. ^ Kennedy, A. S., & Kennedy, V. (2013). Animals of the Masai Mara. Princeton University Press.
  66. ^ Owen T. R. H. (1951). "Notes on the feeding and other habits of the crocodile". Sudan Wild Life and Sport. 2 (2): 33–5.
  67. S2CID 86595859
    .
  68. ^ Baldus R.D. (2005). "Community in Tanzania to Harvest Problem Crocodiles". African Indaba E-Newsletter. 3 (3): 20.
  69. ^ a b "Nile crocodile". Philadelphiazoo.org. 25 July 2003. Retrieved 25 April 2013.
  70. ISBN 9780198508236
    .
  71. ^ "African Elephant – Animal Facts". Switcheroozoo.com. Retrieved 25 April 2013.
  72. ^ Selous, F. C. (1908). African nature notes and reminiscences. Galago.
  73. ISBN 093989517X
    .
  74. ^ Quammen, D. (2004). Monster of God: the man-eating predator in the jungles of history and the mind. WW Norton & Company.
  75. ^ Bailey, T. N. (1993). The African leopard: ecology and behavior of a solitary felid. Columbia University Press.
  76. ^ Brottman, M. (2013). Hyena. Reaktion Books.
  77. doi:10.1111/jzo.12052
    .
Retrieved from "https://en.wikipedia.org/w/index.php?title=Dietary_biology_of_the_Nile_crocodile&oldid=1210374556"