[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: (Long) word from the sole "non-stealthy egg" believer



[All right, as per Chris' message, I'm letting this thread die.  If
 others have parting shots I may accept them, but personally I'd
 prefer it if you'd go on to other topics.  John, if you want to
 respond to this message, you have Ron's address... -- MR ]

At 03:12 22/11/96 -0500, John Bois wrote:

>Similarly, I can say some things about dino reproduction that
>must be true.  You can only do one of two things if you lay eggs:
>hide them or defend them.  This is a fact!

No, it's actually a gross oversimplification.  First of all, there is at
least one major third option: establishing your nest in a spot that
potential egg predators cannot reach, in which case you neither have to
hide them nor defend them.  Secondly, even if no defense is necessary there
are other (and perhaps more important in some cases) factors determining
how much investment of time and energy a parent will devote to a clutch of
eggs.  These include fairly obvious things like thermoregulation/brooding;
for example, aside from the obvious sitting on eggs that most birds do some
desert birds like sandgrouse and coursers fly long distances to wet their
feathers with water to cool their eggs - an energetic cost of breeding in
dry areas that has nothing to do with nest defense or predation.

Further, and perhaps most crucially, there are more subtle strategies that
determine whether a parent devotes large amounts of energy to breeding, and
these relate to the tradeoff between the value of investing energy to bring
a current clutch to fruition and the long-term reproductive output of the
breeding animal.  For example, some birds will abandon a clutch in hard
times, presumably because sticking with it would be unlikely to be
successful and might well weaken the bird to such a degree that it would be
unable to lay future clutches.  The point here is that animals do NOT tend
to wear themselves out defending their clutch to the last gasp; if
predation is a problem they may adopt the strategy (one Mr Bois does not
even consider) of laying numerous small clutches as insurance that if one
is predated others may survive.  This is an evolutionary response that has
nothing to do with the sorts of things Mr Bois is talking about.

> You cannot just leave them lying around because they will be eaten.
>And, if you can't hide them--and let us restrict our argument to big
>dinos--then defending them _must_ be a problem simply because things
>bigger, meaner, and nastier than you push you off your nest and eat
>your eggs.

In fact egg predators are often smaller and stealthier than their victims.
Certainly I would like to know what "bigger, meaner and nastier" critter
pushed female T. rex's off their nests!

>Fighting back runs the risk of injury.  This is a fact and a
>problem.  You can run away and abandon your nest, but this gets
>expensive especially since, if birds are in any way a model, good
>nesting sites are hotly contested.

Good nesting sites are NOT hotly contested for all birds.  They are
certainly limiting factors for, say, birds that nest in natural tree
cavities, but may not be at all for many territorial songbirds with many
potential sites within a defended area.  There is so much variation in what
birds do here that birds cannot be used in general as a model of what
dinosaurs may have done beyond noting, as I have said, that the range of
possible strategies is considerable. I strongly recommend that Mr Bois do
some reading on the breeding strategies of living animals - I think he is
in for a surprise.

>     Big dinosaurs _must_ either stand and fight or abandon the nest.
>This deficiency is seen in stark contrast with placental
>reproduction.  Placentals can just run away from a predator keeping
>baby safe inside.

There are a number of living birds known to move their eggs if necessary; I
believe crocodiles do the same thing.  Anyway, birds rarely, if ever,
"stand and fight" over nests, but use distraction displays and other
devices to ward off potential predators.

In any case this scenario is quite different from what Mr Bois proposed
earlier.  If the nest predators were actually animals so large and fearsome
that they posed a risk to brooding dinosaurs, they could hardly have been
mammals.  What were they?  Other dinosaurs?  And if that was the case, why
did THEY go extinct?  Mr Bois' proposal only works if the animals doing the
predating survived past the dinosaurs they supposedly eliminated.  I doubt
very much that a breeding T rex had much to fear in terms of battles royal
from the kinds of mammals that were around at the K-T!

>  I think you have criticized this view in the past claiming that
>pregnant mothers are subject to increased predation.  If so it is
>you who must provide evidence.

I have not proposed this, but I note that mammal investment in young does
not stop at birth.  Studies by Dr Joel Burger of the University of Nevada
on black rhinos in Namibia, for example, showed that mothers that had been
artificially dehorned suffered 100% calf mortality in the first year in
areas with populations of lions or hyenas.

>All things considered...the overall eutherian adaptive survival
>complex suggests superiority."  And I would add that, at least in
>non- stealthy niches, this mode has it all over the egg as well.

Except that there are more species of bird extant today than mammal.  More
species of reptile, too.  Not to mention the fact that there are still
quite a few marsupials around, and some like the Northern Opossum are
aggressively expanding their range in North America, placentals or no
placentals.

>Mammals may or may not have played a role in dino nest predation.
>But, inasmuch as they were able to simply run away from what I
>believe was an increasing egg-predation load toward the end of
>the K/T, they were the victors not in a war of direct
>competition, but of reproduction--of survival of the fittest.

You have still failed to present any evidence that there WAS an increasing
egg predation load towards the end of the K-T!

>Mammals: "In contrast (to the Early Cretaceous eutherians [whose
>teeth] probably functioned best in insectivory), the structural
>differentiation seen in the dentitions and postcranial skeletons of
>Late Cretaceous forms suggests the existence of diversified habits.

May I point out that the Late Cretaceous lasted a long time, and that it
was not restricted to the period immediately before the K-T?  And that dino
evolution proceeded during that time?  And that adaptations to breeding
stresses may possibly develop rather rapidly?

>    Within this range of possible diets, egg predation _must_ be
>included.  Mammals of today eat eggs, reptiles of the past ate eggs,
>birds eat eggs, all God's children eat eggs--I believe the burden
>rests with you to say why mammals would _not_ eat eggs.  And, as
>noted above, this possibility increased toward the K/T.

I'm sorry, but that is simply not borne out by what you say.  Increased
diversity does not mean more concentration on one resource - it may well
mean less, as new niches are exploited..

>     Mammals provided a threat the dinos had never seen before.
>They were stealthy, intelligent, aware, capable of exploiting new
>diets (with the likely inclusion of dino eggs), and they get
>about at night when the dinos could not protect themselves very
>well.  Previously, I think the dinos only response to egg
>predators was to grow bigger, the better to defend.  But this was
>no strategy against the new little mammals.

Nonsense.  They had lived with mammals throughout the whole of their
evolution, and  with reasonably advanced mammals for millions of years
during the late Cretaceous.  And, AS I have repeatedly pointed out, there
are MANY possible alternate strategies to deal with egg predators, and you
have not addressed why these strategies would not have been available to
dinosaurs.  Increased size is not only not the only one, it is likely that
it would in fact have had little to do with nest defense.  You don't have
to be twelve meters long to drive off a mammal the size of a squirrel.

>Just as dinosaurs had red blood, birds preyed on eggs.  And, since
>they were more able at the K/T, they most likely took a higher toll
>on dinosaurs than their more clumsy relatives, the enantiornithines
>(which, I read on this list, have been found in association with
>dinosaur nests!).

Again you are confusing the Late Cretaceous with the K-T, not to mention
ignoring the possible impact in previous periods of pterosaurs etc.  And
again, if birds are so good at this why are there still creatures like
penguins around (who suffer considerable egg predation from skuas)?  They
ought to have been wiped out ages ago.  Besides, you don't have to be a
champion aerialist to get at eggs, which run very slowly outside of a
frying pan.  I see no reason for supposing that the enantiornithes could
not have been egg predators too.

>  Feduccia (_Science_, 267 Feb. 1995) found a small almost "modern"
>bird from just before the K/T.  With astounding arrogance he claims
>that from this species came all modern birds.  It survived the K/T
>catastrophe, he says, by cracking crabs on the shore.  But this is
>dependency on negative evidence.

Well, not having read the paper, I would point out that as modern birds DO
crack crabs on the shore, I see no reason why that should be any more a
conclusion from "negative evidence" than concluding that it ate eggs or
anything else.

>Ron Orenstein says: "Please explain what dinosaur nesting habits
>could possibly have had to do with the extinction of mosasaurs,
>enantiornithine birds, belemnites, ammonites, large numbers of
>foraminiferan taxa and others at the K/T."
>
>Nothing.  But I'm not sure you can bunch these extinctions
>together.

Well, quite a coincidence then, wasn't it? If you want to be parsimonious,
I think it is far more so to conclude that a common factor was involved in
the broad-based extinctions occurring at the end of the K-T rather than a
bunch of unrelated ones.

>     Ostriches and emus have a very precarious existence.  Male
>emus lay on the nest, fasting for the whole time, in a torpor
>(surely this is an adaptation to avoid predator-alerting visits
>to and from the nest).

Your assumption that such a strategy is "precarious" is rebuttable by
pointing out that it works.  Emus are not only not rare, but (according to
the Handbook of the Birds of the World), despite extensive persecution by
man its populations are stable and even increasing in some areas.

Ostriches, in fact, do not do this; females brood during the day, relieved
by the males at night.  Rheas have the interesting strategy of abandoning
some eggs which then rot and attract flies, which the brooding male eats!

The brooding may, in fact, not just be for predator avoidance; it may also
serve the purpose of thermoregulation (in fact that is probably its primary
purpose), and possibly in the case of polygynous species preventing females
fertilized by other males from laying in the nest (certainly in other birds
brood parasitism is an issue, too).

All of these birds, I repeat, evolved in communities with thriving
populations of mammals, reptiles, birds, etc etc - they were not island
isolates living under near-predator-free conditions, and they are not
"stealthy nesters".  Mr Bois' view would imply that such creatures would be
helpless under such conditions; nonetheless they have evolved and even
flourished.

>     But back to my point which is that just as the birds depended on
>the jaguars (because they ate their predators) so might ratites
>depend on mammals because may keep down those species in dry area
>(for the ostrich and emu at least) which give them the most
>problems--lizards.  I don't know about NZ in this, though, what with
>no mammals to speak of, or reptiles much either???

I am curious as to what sort of lizard could manage to deal with an ostrich
egg.  Have you ever tried to break one?  You practically have to jump up
and down on it.  In fact the chief egg predators of ostriches appear to be
jackals, hyenas or Egyptian Vultures (which use stones to break the eggs).
Also, I note that ostrich breeding success is, in fact, low - only about
10% of the eggs laid hatch.  And yet - they survive!  In other words, they
have ADAPTED to a low level of breeding success.  So could dinosaurs have
done.

There is, mind you, one ratite that does seem to be suffering from egg
predation, namely the Australian Cassowary, which suffers losses from feral
pigs - but pigs are a very recent addition to the scene deliberately
introduced by man, and therefore do not correspond to anything we know
happened at the K-T.

As for emus, I note that large reptilian predators certainly stalked
Australia (and a few like the perentie still do), and I doubt that they
were "kept down" by mammals.  In NZ the only surviving ratite is a burrow
nester that takes particular care to choose extremely-well camouflaged nest
sites, often waiting months or years after a burrow has been dug before
using it to allow vegetation to grow over the entrance.

>But birds could hide _their_ eggs in even further out-of-
>the-way places.  One thinks of migratory swans, geese, penguins
>of the antarctic.  These luxuries of stealth were not available
>to the egg mountaineers.  And even stay-at-home birds have a much
>greater ability to extend their nest-to-foraging-site distance.
>All of this means that birds have a greater selection of stealthy
>sites than did dinosaurs.  This is a fact.

It is also a fact that many island-nesting waterbirds make not the
slightest effort to hide their eggs or conceal the sites in any way, and so
do not indulge in "luxuries of stealth" - and survive all the same.

>     As for dinos carrying babies: Are you seriously suggesting
>that dinos carried their eggs from safe house to safe house in
>order to fool egg predators, perhaps in the dead of night?

Why not?  Some birds do, on rare occasions, and so, I believe, do some
crocs.  BTW, crocodiles are not, as you say, exempt from egg predation.
Caiman eggs are eaten by tegu lizards, coatis, foxes  and monkeys, with the
first two being the most important, and the females must guard the nests in
consequence. Nile monitors and other predators destroy some 50% on average
of eggs of Nile crocodiles. (Source: Crocodiles and Alligators, CA Ross
ed.)  And of course a number of fishes literally carry their eggs around in
their mouths until hatching.

>But this is not right.  I have the evidence of my senses to base
>it on.  As I walk around this world, in the forests, in the
>suburbs, in the cities, on the farms I NEVER SEE A NON-STEALTHY
>EGG.

Then you don't spend much time where ratites breed.  And you probably
aren't looking with the efficiency of an egg predator.  And I'll bet you
see lots of non-stealthy nests (and if you can find the nests you can find
the eggs, can't you?).  Take a walk through a gull colony; there are
literally tens of thousands of non-stealthy gull eggs laid every year on
the Leslie Street Spit not far from downtown Toronto (Not to mention our
Canada Geese breeding in city parks, whose nests are non-stealthy and can
be found easily).  Drive down US 1 to the Florida Keys and count the
non-stealthy Osprey nests sitting on telephone poles.

Non-stealthy eggs are everywhere!

>3. The need of dinosaurs to get moving directly after hatching
>means potentially helpful developmental programs must be
>curtailed to get motor programs up and running (a big dinosaur's
>baby would hatch--probably--after about a month or so.  Elephant
>baby's develop securely for 10 months [I'm guessing]. 

18-22 months.  And who said baby dinosaurs needed to be up and moving right
after hatching?

>4. Lactation was advantageous.

And yet there are thousands of highly successful tetrapod species alive
today who get along without it.

>4. In breeding season dinos must either stay at the nest (using
>energy stored in their body--some crocs and emus do this), or
>forage near the nest (returning to provision the guard).  Mammals
>can range freely, moving at a moment's notice with babies on
>board.  Mammal options are more flexible.  This is a fact.

Many mammal species, including foxes, bears, pumas and others, den their
young and revisit them regularly with food long after their birth.  Many
deer depend, not on moving their young, but on hiding cryptically-coloured
young for long periods in one spot.  Again, you are grossly oversimplifying
nature.

>     Now, all of this is not meant as a paean to mammalhood.  I
>list the advantages to compare their reproduction with dino's.

These are different strategies, not necessarily across-the-board better
ones - if they were there would be no birds left.  You must realize that
just because mammals have developed a good strategy, that doesn't imply
that other groups can't come up with equally effective strategies of
another type - or that just because eutherian strategies are good, that
doesn't mean that all other strategies are doomed to failure.

>Now my argument benefits from an accumulation of circumstantial
>evidence, viz., very few non-stealthy egg layers exist;

On the contrary, there are lots of them.  See above.  And we don't know, to
repeat, whether dinosaurs were generally "non-stealthy" at all!

>advantages of stealthy egg laying are patent;

And some dinosaurs, particularly small ones, may have been stealthy nesters
- and stealthy egg laying is NOT necessarily more advantageous than other
techniques such as non-stealthy egg-laying in colonies in protected
situations, as in gulls.

>open-field niches are dominated by secure reproducers (mammals);

This may have far more to do with the fact that only mammals have evolved
the type of dentition that can handle grasses in any amount; and in any
case the type of "open-field" grass-dominated habitats we have today did
not exist in the Cretaceous.

>Yes.  They could have layed many small clutches.  But this
>doesn't mean it was "inexpensive".  The cost of the egg itself
>may well have been infinitesimal, but its defence was not.

Yes, it may have been, if abandonment to lay another clutch was triggered
when the investment cost rose above a certain level.

> And the strategy you are apparently suggesting for the dinosaurs,
>of spraying their eggs all around the country side in the hope that
>some of them will hatch, does not seem feasible to me.

Except that some animals do exactly that today.

>Besides, many dinosaurs layed quite elaborate nests which took much
>investment (like megapodes).

I know of no dinosaur that built megapode-style mounds; nor do we know, I
think, how much time it took for (say) a maiasaur to construct a nest.  For
a creature that size it might have been a rather rapid and easy process.
Further, my understanding is that some dinosaurs are known not to have
built nests at all.

>Some dinosaurs were colonial nesters for whom your excess-egg idea
>wouldn't work.

But then the "safety-in-numbers" concept of colonial life kicks in - and in
fact in arid areas like central Australia some colonial waterbirds WILL
abandon entire colonies and re-nest elsewhere or later in hard times.

--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                 
Mississauga, Ontario, Canada L5L 3W2          Internet: ornstn@inforamp.net