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Re: Sundry responses of Bois



At 03:47 PM 5/30/00 -0400, Ronald Orenstein wrote:

Refuting John Bois' egg predation "explanation" for dinosaur extinction
 successful large egg layers depend on
grass (a concealing medium which did not exist at the K/T), or
wetlands;

This statement does not apply to many successful species of ground-nesting birds and reptiles today which are neither inhabitants of grassland or of wetland areas, including many tortoises and birds like the ostrich,

In addition, while *grass* did not exist, its ecological niche was handled by *ferns*. And bracken fern prairies offer at *least* as good a hiding place for eggs as grass prairies.


wetlands and grass are more effective mammal insulators than
other biomes;

I see no evidence of this whatever. There are a number of successful wetland-dwelling mammals from many different lineages, including predators as large as the tiger and a small as a water shrew.

And as generalist as various rats - which most definitely eat eggs (among other things)!


As for grasslands, anyone who has taken a trip to the African savannas would have a hard time understanding that such areas are mammal-poor.

Or go back 50K years in North America, prior to the big-game extinctions here.

If someone discovered big terrestrial egg
layers and mammals (particularly placentals) living in harmony--without
having to hide, I would run away
forever.

As it has been repeatedly pointed out that this is indeed the case for ostriches and emus, both of which coexist with potential nest predators and often nest in open, completely unconcealed situations, I am inclined to doubt this promise.

Havong seen film footage of ostrich nests, I concur with this characterization - the nests can be quite exposed indeed. The female, however, guards it *violently*.


There is certainly no question that any animal, whether it lays eggs or not, may be highly vulnerable at the reproductive stage. However, a constraint is not an eliminating factor. That dinosaurs suffered from nest predation would seem to be so obvious as to almost not require verification;

But naturally.

that they were so incapable of defending themselves against nest predators that this factor became the primary or sole contribution to their final extinction is a very different kind of claim indeed, and one that is not obvious in the least.

I would really like to see any animal try and steal eggs from a Troodon! (Assuming it didn't hide its nests, that is). Such an attempt is likely to end up with the would-be thief becoming the dinner.


 This proposition is being actively studied in
birdland.

It may well be that the number of Island birds were wiped out by introduced nest predators such as rats, but in every case that I can think of the introduced animals could also have killed adults (including incubating adults - something that may welll have a greater effect than clutch loss).

Not to mention *human* egg predation, which will have been several times more efficient than that of almost any other animal. Our success rate in food acquisition is unheard of. Even well hidden nests, like those of sea turtles, are easily over-exploited by *human* hunters.


And, killing of incubating/gravid females is indeed often more deleterious to a population than killing the young (including eggs). It was large-scale disruption of nesting females - for their feathers - that drove the Passenger Pigeon to extinction.

--------------
May the peace of God be with you.         sarima@ix.netcom.com