The ostrich (Struthio camelus) has a small brain, perhaps even relative to phasianid birds

It is easy to show that the ostrich (Struthio camelus) has a small brain relative to like-size ungulates - with which it is ecologically comparable.

What is more subtle is an allometric comparison of brain sizes between the ostrich and trophically comparable but far smaller birds, particularly Phasianidae (https://en.wikipedia.org/wiki/Phasianidae).

In this Post, I suggest that the ostrich is, if anything, rather small-brained for a phasianid of its body size. It seems to be, in a sense, nicely preadapted for domestication.

Source: Hrdlicka A (1907) Brain weights in vertebrates. Smithsonian Miscellaneous Collections XLVIII: 89-112.

'Numida cristata' body mass 467 g, brain mass 3.0 g

Numida data in Crile and Quiring (1940)

Pavo cristatus female adult, body mass 3060 g, brain mass 6.7 g

Lophortyx californicus adults, body mass 151.8 g and 102 g, brain mass 1.22 g and 1.5 g

Callipepla squamata adult, body mass 99 g, brain mass 1.5 g

Bonasa umbellus female adult, body mass 299.3 g, brain mass mean 2.7 g

Colinus virginianus, both sexes, all adults, n = 20, body mass mean 125 g, brain mass mean 1.228 g

Gallus gallus data in Crile and Quiring (1940)

The brain of the ostrich is mean 42.11 grams at say 55% of body mass 123 kg, = 67.65 grams. Its head weighs mean 0.68 kg. at carcass mass 59.9 kg.

Casuariiformes: Dromaius novaehollandiae female adult body mass unrecorded, brain mass 20.3 g

Casuariiformes: Casuarius casuarius sex unknown adult body mass unrecorded, brain mass 31.7 g

My plotting of a regression, using the above data, suggests that a domesticated phasianid, viz. Gallus gallus, has been decephalised by selective breeding.

However, both the ostrich and Casuariiformes have brains smaller than expected, based on the allometry of wild phasianids.

Posted on May 19, 2024 09:15 PM by milewski