Comparison of body composition in the Maasai ostrich (Struthio camelus massaicus) and a coexisting phasianid, the yellow-necked spurfowl (Pternistis leucoscepus)

INTRODUCTION

Ostriches (Struthioniformes, https://en.wikipedia.org/wiki/Struthioniformes) can in some sense be viewed as scaled-up galliforms (https://en.wikipedia.org/wiki/Galliformes).

Furthermore, the Maasai ostrich (Struthio camelus massaicus, https://www.inaturalist.org/observations?taxon_id=322201) coexists with various galliform families, genera, and spp., including the yellow-necked spurfowl (https://www.inaturalist.org/taxa/495989-Pternistis-leucoscepus).

However, ostriches can alternatively be viewed as quasi-ungulates, integrated into a complex guild of Artiodactyla and Perissodactyla in Africa and - historically - Eurasia.

This is mainly because - contrary to popular belief - ostriches are not so much omnivorous as specialised for herbivory.

AIMS

With this ambivalence in mind, I was curious to compare the Maasai ostrich (hereafter referred to as the ostrich) with the yellow-necked spurfowl (hereafter referred to as the spurfowl) with respect to the proportional sizes of various organs in its body.

Is it the case that the ostrich scales relative to the spurfowl as, for example, the lion (Panthera leo) scales relative to the domestic cat (Felis catus), as detailed in Davis (1962, https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1558-5646.1962.tb03240.x and https://www.jstor.org/stable/2406182 and https://onlinelibrary.wiley.com/doi/10.1111/j.1558-5646.1962.tb03240.x and https://academic.oup.com/evolut/article-abstract/16/4/505/6867898?login=false)? Or are there basic differences in the sizes of organs, unexplained by mere scaling?

STUDY SPECIES

For an introduction to the spurfowl in question, please see:

https://ebird.org/species/yenspu1/L3028880

https://www.google.com.au/search?q=Yellow-necked+spurfowl&sca_esv=f9529c069ef53509&sxsrf=ADLYWIKMXM1hF3wGgITFx8oJLiMSlJTHnQ%3A1716248001529&source=hp&ei=wd1LZu-rHtPs1e8PkqGECA&iflsig=AL9hbdgAAAAAZkvr0QCE8ho7MIAM1URxQ-8YOIC3NDCa&ved=0ahUKEwivkOeDsp2GAxVTdvUHHZIQAQEQ4dUDCBc&uact=5&oq=Yellow-necked+spurfowl&gs_lp=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_qnAg&sclient=gws-wiz#fpstate=ive&vld=cid:9f8d02bc,vid:EjzMyaiP_sU,st:0

STUDY LOCATION

Wildlife Ranching and Research, later Swara Plains Conservancy, now incorporated in Nairobi National Park
1987-1988

RESULTS

All of the following values are mean masses as % of mean body mass, except where stated otherwise.

The values are

• first for the adults of the ostrich (for sample size see other Posts), and
• second for the spurfowl (n = 3 adults).

Dressed carcass 49%, 67%
Total limb 49%, 33%
Feet 4%, 3%
Head 0.6%, 4%
Skin (includes skin of wings?) 4.5%, 4.5%
Skin and feathers 6%, 12%
Total visceral organs 6%, 3%
Cardiovascular organs 3%, 1%
Cardiovascular organs as % of total visceral organs (excluding gastrointestinal tract) 55%, 39%
Eyeballs 0.085%, 0.67%
Eyeballs as % of head (including eyeballs) 15%, 18%
Gastrointestinal tract 21%, 9%
Contents alone of stomach 3%, 6%

Length of small and large intestines as %o of total body length 193o/oo %o, 67.5%o

The following body components showed positive allometry:

• legs including feet (ostrich 46%, spurfowl 22%)
• internal organs including gastrointestinal tract and, specifically, intestines (organs: ostrich 6%, spurfowl 3%; intestine length: ostrich 52%, spurfowl 19%)

Despite the large, sturdy legs and feet of the ostrich, its feet are more simply constructed than those of the spurfowl, with only two toes instead of three.

The following body components showed negative allometry:

• dressed carcass (ostrich 49%, spurfowl 67%),
• head, including eyes (ostrich 1%, spurfowl 4%),
• feathers (ostrich 6%, spurfowl 12%),
• wings (ostrich 2%, spurfowl 8%), and
• pectoral muscles (obvious).

The ostrich had a proportionately longer oesophagus than that of the spurfowl. However, the masses, relative to body masses, did not differ.

The full and empty proventriculus of the ostrich were statistically significantly heavier, relative to body mass, than the full and empty crop of the spurfowl. However, the volumes (measured by filling the emptied organs with water) did not differ, relative to body mass.

The full and empty gizzards did not differ in mass, relative to body mass, in the ostrich and the spurfowl.

The stomach (comprising crop, proventriculus, and gizzard) did not differ in mass, whether full or empty, relative to body mass, in the ostrich and the spurfowl.

In the case of the small intestine, lengths, and full and empty masses, did not differ, relative to body masses, in the ostrich and the spurfowl. However,

• volume (as measured by filling the emptied organ with water) was statistically significantly greater in the ostrich than in the spurfowl, and
• surface area was statistically significantly smaller in the ostrich than in the spurfowl.

The full mass, length, and volume (as measured by filling the emptied paired organs with water) of the caeca were statistically significantly greater, relative to body mass, in the ostrich than in the spurfowl. The surface area was statistically significantly smaller in the ostrich, relative to body mass, than in the spurfowl. The empty masses, relative to body masses, did not differ significantly.

The large intestine was statistically significantly greater in the ostrich than in the spurfowl, relative to body masses, in full masses, empty masses, and lengths.

The gastrointestinal tract may be divided into foregut and hindgut.

The foregut, consisting of the stomach in a loose sense, contributed a similar proportion of body mass in both spp. However, the stomach is composed of

• two parts in the ostrich, compared to
• three parts (thin-walled crop, tubular proventriculus, and gizzard) in the spurfowl.

In the hindgut, the large intestines show the greatest contrast between the two spp. of birds.

The small intestine contributes similar proportions of body mass in the two spp. However, that of the ostrich is irregularly constricted at intervals of about 20-25 cm, and the chyme tends to form boluses far drier than the fluid chyme of the spurfowl.

The caeca of the ostrich alone contains spiralled, mucus-lined septa, apparently restricting the movement of contents.

The large intestine is extremely long and bulky in the ostrich, weighing 42% of all visceral organs and their contents. By contrast, the large intestine is rudimentary in the spurfowl.

The first half of the large intestine of the ostrich is an exaggerated version of the caeca. The spiral septum is wider but has a tighter spiral, which restricts movement of the contents to the extent that I found, while collecting the data, that manual emptying of the tube was impossible.

In the ostrich, the contents of the caecum and initial section of the large intestine are fluid. By contrast, farther down the large intestine boluses are formed, with obvious progressive desiccation towards the cloaca, where fecal pellets occur.

DISCUSSION

For useful background, please see

• https://www.researchgate.net/figure/Gastrointestinal-tract-of-an-ostrich-A-glandular-stomach-B-gizzard-C-small_fig3_352775611
• https://www.researchgate.net/figure/The-digestive-system-of-an-adult-ostrich-adapted-from-Holtzhausen-Kotze-1990-A_fig2_227868244
• https://www.researchgate.net/publication/227868244_Anatomy_and_physiology_of_the_gastro-intestinal_tract_and_growth_curves_of_the_ostrich_Struthio_camelus
• https://physoc.onlinelibrary.wiley.com/doi/pdfdirect/10.1113/expphysiol.1984.sp002870.

The relationship between the ostrich and the spurfowl is unsurprising (in line with other animals of different size), in that the larger bird has proportionately:

• smaller eyes and brain,
• bigger bones,
• bigger cardiovascular system, and
• smaller metabolic organs.

Both the volumes of the proventriculus/crop and the combined masses of the stomach components are similar, relative to body masses, in the ostrich and the spurfowl.

The skin is also isometric in the two spp.

This is noteworthy, because the skins of larger animals are usually proportionately thicker than those of smaller animals, despite proportionately lesser surface areas.

For example, the mass of the skin (excluding that of head and lower legs), relative to body mass, is as follows (n = 20 for each species) in ruminants coexisting with the ostrich in the study area:

• Eudorcas thomsonii thomsonii 0.56 kg/21kg = 2.7%
• Nanger granti granti 1.34 kg/50 kg = 2.7%
• Alcelaphus cokii 5.23 kg/130 kg = 4.0%
• Connochaetes albojubatus 8.31 kg/200 kg = 4.2%

This positive allometry may be because larger-bodied spp. tend to

• be vulnerable to parasites,
• possess areas of bare skin (applicable also to the ostrich), and
• experience greater stresses on the skin because of percussion/friction by/with extraneous objects.

The skin of the ostrich is proportionately thin, compared to that of like-size ungulates. However, it is proportionately heavier, probably because it is denser (as evidenced by the durability of ostrich leather).

The large legs and feet, and small wings and feathers (and body cage), of the ostrich could be owing to its large body size, or to its flightlessness. However, the two attributes are related anyway. (are the wings of large flightless birds positively allometric, thus emphasising the oddness of the ostrich?? - see literature).

It is remarkable that the pair of legs (including the feet) of the ostrich approaches half of body mass. The leg bones of the ostrich seem disproportionately heavy, possibly because of a disproportionate risk of shattering in such a heavy bird.

There is obvious convergence with ungulates in

• the hoof-like foot (https://www.dreamstime.com/feet-ostrich-close-photo-struthio-camelus-image133768866 and https://www.flickr.com/photos/davidbygott/4435592786 and https://www.istockphoto.com/photo/ostrich-feet-gm179285516-3477888 and https://www.researchgate.net/figure/Three-dimensional-reconstruction-of-ostrich-left-foot-and-the-model-ostrich-for-trials_fig1_318683284 and https://www.researchgate.net/figure/Fig1-Right-phalanges-of-an-adult-ostrich-anatomical-specimen-Clockwise-from-top_fig1_50351251), and
• the long, muscle-free prop of the lower legs (= tarsometatarsus in the case of the ostrich, https://www.dreamstime.com/stock-image-ostrich-chick-image20033401 and https://www.dreamstime.com/stock-photography-ostrich-feet-image2329512 and https://www.dreamstime.com/royalty-free-stock-photo-ostrich-image866415).

Posted on May 20, 2024 04:34 PM by milewski