Diet of the feral dromedary (Camelus dromedarius) in Australia, part 1

Camelus dromedarius (https://en.wikipedia.org/wiki/Dromedary) is unusual among the feral animals in Australia.

Firstly, among all the domestic species of mammals, the dromedary is least closely associated with any known wild ancestor - despite domestication having occurred as recently as four thousand years ago.

Secondly, this is the only feral ungulate successful in the extensive nutrient-desert that I have called the Australian Empty Quarter (see my last Post and https://www.researchgate.net/figure/Map-of-project-study-area-showing-the-camel-distribution-boundary-major-desert-features_fig1_255687533).

Thirdly, the dromedary has such slow metabolism, growth and reproduction, relative to most other artiodactyls, that it seems somewhat convergent with extinct large marsupials (e.g. https://en.wikipedia.org/wiki/Palorchestes) of the Pleistocene in Australia (none of which is known to have occurred in the Australian Empty Quarter).

Given how odd the dromedary is for a domestic herbivore - resembling a wild animal 'pre-adapted' for the Australian semi-arid zone - its diet in its adopted habitat (https://dpir.nt.gov.au/__data/assets/pdf_file/0004/233455/tn116.pdf and https://www.dreamstime.com/stock-photo-australian-camels-outback-pair-wild-dromedary-graze-image34710910 and https://www.alamy.com/dromedary-camels-two-grazing-camelus-dromedarius-feral-animals-living-wild-introduced-to-australia-now-widespread-in-wild-image181672328.html) is of obvious interest.

What can we say about the ecological nature of those genera and species of plants most preferred by the dromedary in its feral state in Australia?

The overall finding is hardly surprising. The preferred plants tend to belong to:

  • cosmopolitan genera and weedy species
  • nutritional categories which boost palatability (e.g. nutrient-parasitism and symbiotic nitrogen-fixation)
  • genera and species restricted to the patches of relatively nutrient-rich soils (by Australian standards), and
  • regeneration after wildfires.

The plant species preferred by the dromedary in Australia are generally not the dominant/commonest ones, and this is particularly so in the Australian Empty Quarter. Instead, they tend to belong to families such as the Amaranthaceae, possessing soft foliage and growing on the least acidic soils or as temporary flushes dependent on ash.

Favourite food-plants of the feral dromedary, in the category of symbiotic nitrogen-fixers, belong to the Mimosaceae and Fabaceae.

In the former family are Acacia oswaldii (https://en.wikipedia.org/wiki/Acacia_oswaldii and http://worldwidewattle.com/speciesgallery/oswaldii.php) and several other species in the same genus, some of which are spinescent (http://worldwidewattle.com/speciesgallery/descriptions/pilbara/html/victoriae.htm and http://worldwidewattle.com/speciesgallery/descriptions/pilbara/html/tetragonophylla.htm)

In the latter family are Erythrina (https://en.wikipedia.org/wiki/Erythrina_vespertilio), Crotalaria, Indigofera, Rhynchosia, and Swainsona (https://en.wikipedia.org/wiki/Swainsona)

Favourite food-plants in the category of parasites (including both mistletoes and free-standing shrubs which parasitise the roots of other plants) are Amyema, Anthobolus, Cassytha, Cuscuta, Lysiana (https://en.wikipedia.org/wiki/Lysiana_exocarpi) and Santalum spp. (https://en.wikipedia.org/wiki/Santalum).

Other favourite food-plants tend to belong to genera occurring naturally on several continents, some of which can be called cosmopolitan.

These are (in alphabetical order):

Atriplex
Boerhavia
Calandrinia
Capparis
Carissa
Chenopodium
Cleome
Glycine
Ipomoea
Jasminum
Kali (https://en.wikipedia.org/wiki/Kali_(plant))
Lepidium
Marsdenia
Pittosporum
Pterocaulon
Portulaca
Psydrax
Senecio
Sida
Tribulus
Trichodesma
Tripogon
Ventilago
Zygophyllum

The following genera are restricted to Australia but associated with sodic soils: Enchylaena, Lawrencia, Maireana, Sclerolaena and Tecticornia.

This brings us to what are perhaps the most interesting of the favourite food-plants, i.e. those belonging to typically Australian families/genera.

These are (in no particular order) as follows:

Eucalyptus gammophylla (https://en.wikipedia.org/wiki/Eucalyptus_gamophylla)
Grevillea juncifolia (https://en.wikipedia.org/wiki/Grevillea_juncifolia) and G. eriostachya (https://en.wikipedia.org/wiki/Grevillea_eriostachya)
Codonocarpus cotinifolius (https://en.wikipedia.org/wiki/Codonocarpus_cotinifolius)
Eremophila longifolia (https://en.wikipedia.org/wiki/Eremophila_longifolia and http://anpsa.org.au/APOL15/sep99-2.html)
Brachychiton gregorii (https://en.wikipedia.org/wiki/Brachychiton_gregorii)
Lechenaultia divaricata (https://en.wikipedia.org/wiki/Lechenaultia)
Ptilotus spp. (https://en.wikipedia.org/wiki/Ptilotus_macrocephalus and https://en.wikipedia.org/wiki/Ptilotus_polystachyus)
Calotis hispidula (https://en.wikipedia.org/wiki/Calotis_hispidula)
Rhodanthe floribunda (https://en.wikipedia.org/wiki/Rhodanthe_floribunda)
Scaevola parvifolia (https://en.wikipedia.org/wiki/Scaevola_parvifolia)
Stylobasium spathulatum (https://en.wikipedia.org/wiki/Stylobasium_spathulatum).

Atalaya hemiglauca (https://en.wikipedia.org/wiki/Atalaya_hemiglauca) belongs to a mainly Australian genus with one species in southern Africa.

What does the vegetation look like when/where the favourite food-plants of the feral dromedary are so common that they dominate the scene? Here are some glimpses.

Regeneration after wildfire: https://keys.lucidcentral.org/keys/v3/scotia/key/Plants%20and%20Fungi%20of%20south%20western%20NSW/Media/Html/Codonocarpus_cotinifolius.htm

Prominence of phyllodinous acacias: https://www.malleeconservation.com.au/blog/acacia-oswaldii

Prominence of 'saltbush' and other amaranths adapted to sodic soils: https://www.nationalparks.nsw.gov.au/plants-and-animals/saltbush.

to be continued in https://www.inaturalist.org/journal/milewski/58233-diet-of-the-feral-dromedary-in-australia-part-2#...

Posted on October 10, 2021 08:45 AM by milewski milewski

Comments

Really interesting!

Posted by gond almost 3 years ago

@gond I'm glad to hear that.

Posted by milewski over 2 years ago

EVIDENCE OF GEOPHAGY

In December 2001, I watched a documentary about the feral dromedary in Australia, viz.'Silhouettes of the desert', directed by David Curl (https://www.imdb.com/title/tt0272293/ and https://www.screenaustralia.gov.au/the-screen-guide/t/silhouettes-of-the-desert-2000/16700/ and https://www.screenaustralia.gov.au/the-screen-guide/c/david-curl-pty-ltd/2774/). The setting is central Australia (probably near Uluru, https://en.wikipedia.org/wiki/Uluru), during the green season.

The footage included a small group (probably females) attending a small pit dug in firm (calcareous?) earth, ostensibly by the dromedary itself.

We see the animals bite off pieces of earth and eating them wholesale, as opposed to merely licking.

The same documentary contains clear footage of osteophagy, in which the animals take whole bones (ostensibly of the dromedary) into the mouth. They do not seem able to break the bones, raising the question of how much is actually consumed.

Also worth mentioning is graphic footage of an adult male individual of the dromedary breaking down a fairly straight, fairly upright branch of a phyllodinous acacia, thus bringing foliage down within reach of this individual and accompanying females.

The animal gripped the bare mid-section of the branch (about 2.5 m above ground) in his mouth, pulling downwards with the neck, until the whole branch broke (the fracture being at 1-1.5 m above ground). Several individuals are then seen eating foliage that was originally about twice as high as the head of the dromedary in standing posture.

The impression is given (reinforced by the accompanying narrative) that males are strong enough to provide for the group in this way.

Posted by milewski about 1 year ago

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