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RE: Seasonal "Day Care" Hypothesis for Maiasaura



Thanks Carl,
Your points are well taken. I was thinking that this might be a "semi-social" or "quasi-social" kind of situation (I think E.O. Wilson used those terms for some insects that are not completely eusocial, but still show varying degrees of cooperation).
The guards might defend the egg field until the return of all the mothers, and at that point the bird-like squabbling between individuals might resume. Even within a species there can be differing degrees of sociality at different times of year or under other differing circumstances. If predators were to threaten the colony, the squabbling might temporarily cease and possibly even some cooperation as long as the threat lasts (but we probably will never know). For example, some birds might be squabbling away one minute, and minutes later cooperating to drive off a menacing crow or hawk.
My reasoning for limiting the numbers of guards is presumed scarcity of food (the reason most of the herd had to migrate). And being buried, the eggs would not require parental incubation (as you pointed out), just some guarding to minimize losses to the colony as a whole. This would be beneficial to the species' survival, even if the guarding was less successful in some years than in others.
I would be interested to know how Robert Trivers ideas might apply to the proposed seasonal "day care" hypothesis. Anyway, I am not proposing reciprocal altruism anywhere near what might be found in eusocial insects (ant colonies for instance), but still something a little more social than in bird colonies (like penguins), at least during a migratory season (if evidence for such migration is found). I would certainly not expect to find anything like this among predatory dinosaurs (theropods), most of which were probably more territorial and not social, like many of their bird descendants. It just seems like it would be much easier to study behaviors in Maiasaura (even if we don't have thousands of skeletons), compared to theropods (non-avian) whose remains are relatively scarce.
---------Ken
*********************************************************
From: Carl Mehling <cosm@amnh.org>
Reply-To: cosm@amnh.org
To: dinosaur@usc.edu
Subject: RE: Seasonal "Day Care" Hypothesis for Maiasaura
Date: Thu, 11 Jan 2001 10:31:08 -0500

"However, although most of the herd would then migrate to distant
feeding areas, it seems reasonable to me that some small number would
stay behind to guard the site against egg robbers (at least minimize
the damage they might do).  The numbers of "guards" would not have to
be very large, and couldn't be too large as to overgraze the area in
a time of scarcity (and if necessary they could work in shifts to
graze in areas further away).

Criticism welcome,  Ken Kinman"

I've been meaning to reply to this for a while - forgive me if you've
all moved on.

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? Granted, incubation is an issue, but guarding
against predators was also very important. I can't find my copy of
Robert Trivers' Social Evolution to pull out any dazzlers, but I
recommend giving it a look with regard to this thread.

Carl

Carl Mehling
National Center for Science Literacy, Education and Technology
American Museum of Natural History
Central Park West @79th Street
New York, N.Y.  10024
(212) 769-5849
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