The ostrich (Struthio camelus) as a quasi-ungulate, part 3

Fide Steve Goodman (https://www.fieldmuseum.org/about/staff/profile/steven-goodman), pers. comm. 1990

In Egypt, the ostrich avoids slopes, and certainly avoids rocky ground.

(also see https://www.perplexity.ai/search/Is-the-ostrich-D9R6jS7CR2KqfrdE5OxAWQ)

Consumption of Citrullus colocynthis (https://www.inaturalist.org/observations?place_id=7055&subview=map&taxon_id=160657), which is notorious for its bitterness:

The ostrich in Egypt eats the ripe fruits of this wild melon.

The coexisting Gazella dorcas eats the green fruits of C. colocynthis, avoiding the ripe fruits. This is possibly partly because the seeds in the unripe fruits are not yet toxic. It also eats the roots, but not the leaves.

Camelus dromedarius does not eat C. colocynthis.

In Egypt, Equus asinus and Capra hircus eat the fruit and roots of C. colocynthis.

(see confirmation that C. colocynthis is moderately palatable to Capra hircus in https://www.mla.com.au/globalassets/mla-corporate/extensions-training-and-tools/creative-commons/weed-control-using-goats---cc.pdf)

Capra nubiana eats the leaves, the roots, the green fruit, and the dried fruit.

Ovis aries eats only the fruit.

Consumption of Lotus hebranicus (https://www.inaturalist.org/observations?place_id=7055&subview=map&taxon_id=1391532):

This is a food-plant of the ostrich in Egypt. The bird eats the green (unripe) fruits so avidly that one does not observe pods in the field.

Also see:

Osborn and Helmy (https://www.biodiversitylibrary.org/bibliography/2801)

Tregenza L A (1954, 1957) 'Egyptian Years' (https://www.abebooks.com/first-edition/Egyptian-Years-Tregenza-L-A-London/1292008130/bd), and 'The Red Sea Mountains' (Oxford University Press).

https://www.pbs.org/wnet/nature/blog/ostrich-fact-sheet/#:~:text=They%20primarily%20eat%20plants%2C%20but,up%20food%20in%20the%20gizzard.

Misplaced photo of Equus hartmannae:

http://www.zimbabweconnections.com/kylenp-rates/

https://www.researchgate.net/publication/360643439_Diseases_of_farmed_crocodiles_and_ostriches

https://academic.oup.com/chicago-scholarship-online/book/13023/chapter-abstract/166221921?redirectedFrom=fulltext&login=false

RELATIVE MASSES OF FEATHERS/PELAGE IN OSTRICH CF UNGULATES

Robbins et al. (1974) report an individual of Odocoileus virginianus with body mass 63 kg, gastrointestinal contents 6.25 kg (= 9.9% of body mass, bearing in mind that this individual had access to 'concentrate' forage), and pelage mass (oven-dry, and presumably including head, feet, and tail) 0.8173 kg at a time between winter and summer. On this basis, the fresh mass of the pelage was 0.8173 X 1.06 (fide Robbins, pers. comm.) = 0.866 kg. Thus, the pelage contributed 1.37% of body mass.

Data on the ostrich, shared with me by Chris Foggin (Zimbabwe) in 1990, are as follows (bearing in mind that there was probably no attempt to dry out the feathers). Sample size n = 3, mean body mass 91.2 kg, mean mass of feathers 0.9967 kg (0.75 kg, 0.9 kg, 1.34 kg). Thus, the feathers contributed 1.1% of body mass.

Discounting for gut-fill: O. virginianus 1.5%, ostrich a maximum of 1.3%.

Caveat:
The values would be similar between the two spp. if the value for O. virginianus actually excluded the pelage on head, feet, and tail.

My overall commentary:
It seems fair to say that the feathers of the ostrich are no more massive, relative to body mass, than the pelage of O. virginianus. If anything, an ungulate larger-bodied than O. virginianus would have a proportionately smaller surface area, and therefore a reduced value for pelage mass relative to body mass. I speculate that the feathers of the ostrich weigh no more than the pelage of a like-size ungulate, because a) the feathers do not cover all of the body, and b) feathers are, by their nature, lighter per unit of length than is pelage.

Thoughts about a theme of mobility in the ostrich:

Mobility of neck and eyes, boosting anti-predator vigilance
(reflected in head, eyeballs, and neck)

Mobility in rapid running, boosting ability to out-accelerate and outdistance predators
(reflected in heart, lungs, spleen, and legs)

Mobility of skin coverings, boosting ability to thermoregulate
(reflected in skin and feathers/pelage)

Mobility (in terms of both speed and energetic efficiency) in computing among water sources and patches of food, boosting ability to reach resources promptly
(reflected in legs and bipedality)

Mobility in reproduction

Mobility in foraging in the vertical dimension, boosting an ability to switch from foods on the ground to those high on plants

An aspect of mobility lacking in the ostrich: among types of terrain (rocky, sloping, loose sandy, slippery, water demanding wading)

Monogastric/hindgut fermenter is flexible cf ruminant
Difference between equid (quantity necessary) and ostrich
Selectivity of ostrich, because of configuration and chewing done in gizzard and water metabolism and breeding style and...
Water economy facilitates selectivity in the ostrich because it does not have to spend time commuting to water
Contrast the 'retention' strategy of ostrich with more or less all other folivorous birds, which process the stuff quickly (like a panda)

Ingesta (and urine) no lighter, while intestine walls heavier, in ostrich than in ungulates.

Suggests elevated digestive efficiency, in view of reduced intake rates.

Eggs carried at any one time are lighter than foetus, placenta, and associated fluids of ungulates, consistent with elevated growth rate of the juvenile, the large number of young per parent, and the reduced brain mass of the ostrich.

Ostrich has greater body mass and linger legs than ungulates taking a like percentage of dicotyledonous plants and equally independent of drinking. Presumably confers more efficient locomotion.

Ostrich penetrates flat, arid zones beyond range of other monogastric, hindgut-fermenters, i.e. warthog (small, short-legged, large-headed, dependent on water) and equids (dependent on water and food quantity).