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Seasonal "Day Care" Hypothesis for Maiasaura



CAUTION: Much speculating below.
I am really switching gears here, because as a general systematist, I am usually more interested in morphology and genetics, rather than in behavior. However, we were discussing Maiasaura parenting on another list and I came up with the beginnings of a very speculative theory on their overall reproductive strategy (integrating some ideas from others on that list). If anyone wants to comment or criticize it, feel free, as it is my first feeble attempt to dabble in dinosaur behavior.
I named it the Seasonal "Day Care" Hypothesis. Just before migrating on to greener pastures, the Maiasaura herd would lay their eggs in the same spot they had for generations (in a sandy coastal area). 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).
Which females would stay behind in this scenario? Perhaps those with sick or injured children, or perhaps older females who might have trouble keeping up with the migrating herd (and therefore opting for the less stressful guard duty). Or perhaps it would be males instead of females, just like ratite males guard a communal nest, but in this case it is on a much larger scale (and the eggs being buried, a larger site could be defended).
When the seasons changed and vegetation became plentiful once again, the herd would return in time to give protection to the vulnerable young that hatch and immerge from the sand. Small migrations from the communal site would widen the feeding area as necessary. The young grew fast enough that after several months they were big enough to join the adults on the next migration (after another batch of eggs were laid), and the whole cycle repeats itself. Such a seasonal migration, with a small force staying behind to protect the egg field, would seem to me to be an optimal reproductive strategy for Maiasaura.
But perhaps others might prefer something simpler like: migrating with no guards left behind; or parents stay with nest during laying, hatching and rearing (with a shorter migratory season), or an even simpler non-cyclic migration pattern without a fixed homebase for reproduction.
Criticism welcome, Ken Kinman
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