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Re: Nocturnal crocs?

Interesting theories regarding mammal predation on nests 
from all thus far.  I have a couple of thoughts to add.

John Bois 
<jbois@umd5.umd.edu> wrote:
> My mechanism
> is not a "holocaust" at all; it is a slow, steady, abiding selecetion, a
> selection which operates strongly today (at least this claim is supported
> if not known).  Yes, there was a bolide, but, again, what 
> magic-bullet effect
> can account for selective bird extinction.  I mean the big dinos can
> starve due to no food.  What about the little birds?

I don't see how your mammal predation model produces 
selective bird extinction, either.  It seems to me that all 
avians would have problems with a massive nest predator 
boom. Modern birds have many nest predators. Other birds, 
lizards, snakes, small mammals: all of these 
attack nestlings and eggs.  Tree and cliff nesting does not 
stop egg predation. In fact, all oviparous species today, 
be they crocs, birds, lizards, snakes, or turtles, suffer 
significant amounts of nest predation.  These are 
acceptable losses.  Predation of nests does not, and 
probably did not, drive species rapidly into extinction.

There are, of course, a number of mechanisms utilized by 
modern egg-layers to defend nests (otherwise losses would 
be too high). These include concealment and burial, active 
nest defense, mass egg laying (acceptable losses are 
higher), among many others.  Both nocturnal and diurnal 
oviparous animal species exist today, some members of both 
groups nest on the ground, and some members of both groups 
nest in elevated locations. In fact, concealment, active 
nest defense, and nearly any nest protection strategy 
one selects can be found in both diurnal and nocturnal 
oviparous animals.  I honestly do not see there being a 
correlation with nocturnal habits and nest survival.

Another point to consider: even if average mammal size or 
abundance increased in the late Cretaceous, I doubt it 
would make a significant difference regarding nest 
predation compared to the fungal infections, insect 
predators (like ant species), reptile predation, and bird 
predation that would have been common already.  I find it 
hard to believe that mammal nest predation compares much 
to egg losses due to fungal and bacterial infections, or 
that of insects.

Michael Habib
University of Virginia