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Re: Seasonal "Day Care" Hypothesis for Maiasaura



Carl Mehling wrote:
> 
> 
> I would think the number of guards could be no less than half of the herd 
> because animals don't tend to give a damn about individuals that they don't 
> share huge amounts of genetic material with. Unless there was some sort of 
> reciprocal altruism going on, only the parents of a clutch would bother 
> protecting it. I could be wrong, but in most birds, doesn't at least one 
> parent stay with the eggs while the other goes off to eat?

Several species of colony nesting birds form creches. Banded stilts come
to mind - they are extremely territorial of the area around their nest
while incubating, with parents killing any strange chicks that stray
within beak range, but once the chicks reach a certain age this
behaviour is lost completely and semi-independant chicks can wander
willy-nilly. When some parents are off gathering food, a few adults are
left behind as overseers for huge creches of chicks that can pretty much
feed themselves at this point (although can't fly).

Flamingos also form creches once the young have reached a certain age. I
believe that if some late hatching young have yet to fledge when the
flamingo flocks begin to migrate, some adults stay behind for a few days
until the young are ready to fly and thus are able to lead them in the
right direction.

I suspect there are several more species of birds that form creches
where the young are cared for by adult birds that are not their parents,
with large groups of young watched over by just a few adults. Certainly
caimans do, providing a nice phylogenetic bracket for dinos. Since
hadrosaurs probably didn't incubate their eggs directly, it may be
possible for a small number of adults to guard the nests. However the
altricial young would require feeding, so there would have to be a large
number of parents there when they hatched. The parents would also have
to remember where their own nests were located, since I doubt they would
be so altruistic as to feed anyone's young. Once the young could walk
and feed themselves creches may have been an option.

Personally, if I was a hadrosaur I would locate nesting sites in areas
of high food yield, which would not only provide the young with food but
also the adults. Arctic geese come to mind here, with the sudden and
predictable flush of plant growth during the short Arctic summer being
more than enough to provide for both parents and chicks. Although I
would assume that any such suitable area for hadrosaurs would have also
had plenty of other herbivores, and hence lots of carnivores to take
advantage of the fact. If this was the case, then hadrosaurs may have
had more safety in numbers, precluding the formation of pre-hatching
creches. Perhaps hadrosaurs did have some sort of "seasonal daycare"
system, although if birds and crocs are anything to go by it would have
occured once the young had reached a level of independance. Perhaps they
nested quickly and in large numbers, and by the time the young could get
around under their own steam and the local vegetation had been depleted,
the bulk of the adults moved on, leaving a few individuals behind to
look after creches of young until they had grown large enough to be able
to follow.

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Dann Pigdon                   Australian Dinosaurs:
GIS Archaeologist           http://dannsdinosaurs.terrashare.com
Melbourne, Australia        http://www.alphalink.com.au/~dannj/
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