Oolon Colluphid

Hi folks

I’ve had a suggestion from a visitor to my site for another item for the list. Seems like a goody; does anyone have any further thoughts first?

Seems that kiwi eggs are are about six times the size you would expect for a bird of that size. This causes them all sorts of problems, see:
http://www.kiwirecovery.org.nz/Kiwi/...ucinganegg.htm
Also, my correspondent suggested the real (ie not ID) explanation as being:

“Could be that these birds were originally bigger and have reduced in size but their eggs have not.�?

Does anyone (Urvogel?) know if that’s right?

Cheers, Oolon

Undercurrent

IIRC, Kiwis belong to the same order as Ostriches and Emus, and it is a common trend for species that find themselves on islands to become smaller over time. It's definitely not too far fetched to figure the common ancestor would be more emu-sized. I don't know of any fossil evidence, though.

Dean Anderson

Stephen J Gould wrote an essay about Kiwi Eggs ("Of Kiwi Eggs And The Liberty Bell" - republished in "Bully For Brontosaurus") where he makes just that claim.

SEF

A reduction in size of the kiwi but not its egg seems plausible to me. It might be worth trying to cross-check with other groups of birds - especially where the parent stock is most likely known, eg those finches again.

However, I'm not entirely convinced that the difficulty for the kiwi mother necessarily counts as poor design, since there seem to be good advantages for the baby. It might be necessary to show mortality rate is too high because of strain on mother or inability to get food or escape predation (NB kiwi dying out naturally rather than by human intervention) and that the kiwi could afford to be bigger in adult size. Also some animals manage a significant difference in size between male and female. Does the kiwi differ much at all, in which direction and what about its likely ancestors?

Oolon Colluphid

Sure. Well, possibly. It gets a bulk-purchase sized yolk, which must be a head start of sorts. Which, then, makes every other bird with a normally proportioned egg the less-good designs!

But I’m not now sure that the problems the egg’s size causes the females is sufficient grounds to call it suboptimal. It’s another straightforward trade-off, as with mammalian milk. (An infant could get more energy from a given amount of food by eating it directly, as birds do, rather than the mother eating it first and then using it to make milk. The advantages of having a readily digestible food don’t count, because birds manage. But the advantages of receiving countless antibodies offset the disadvantage. At least, one could argue that the infants’ immune systems could fire up on their own -- after all, it was the designer who made the stuff they’re trying to be immune to! -- but it makes the suboptimality claim too complicated to make it worth arguing.) Both milk and kiwi eggs are sort of suboptimal, but not clearly enough to qualify for List Inclusion.

Oolon

MrDarwin

And remind me again why these things have utterly useless wings (which are not even good for display purposes, as with ostriches)?

Urvogel Reverie

This echoes Calder (1978, 1979). The problem is that there is little to no evidence that kiwis are descended from very large ancestors (certainly not moas). I would suggest that Taborskys (1993) is correct in noting that such an explanation as that offered by Calder fails to explain the high yolk and fat content in the egg, and that rather, large hatchling size is selected for. Kiwi population biology strongly suggests that, Taborsky has put it, "Big eggs, big yolks, and big chicks [are] the reproductive ideal."

Urvogel Reverie

Urvogel Reverie

Because God made them that way...duh...

Urvogel Reverie

RufusAtticus

Complete mitochondrial DNA geonome sequences of extinct birds: ratite phylogenetics and the vicariance biogeography hypothesis

Urvogel Reverie

Cooper and his colleagues retrieved a similar topology as well. I would argue that though kiwis closest living relatives are the African and South American ratites, they are most likely directly descended from the Lithornis/Pseudocrypturus or Paracathartes grades within Lithornithiformes. Both share numerous derived characters with Apteryx, particularly in the skull and viscerocranium.

Urvogel Reverie