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Re: Hadrosaur nesting strategy...(was Re: The Life of Birds- Pa
On Sat, 31 Jul 1999, Casey wrote:
> I would argue that one of the prime reasons that Ross's & Snow geese are
> proposed not to migrate into more temperate climates is because they would
> have to compete with the Canada geese which fill a similar niche.
But there are plenty of places which are more productive in which Canada
Geese are not found (further south, for instance).
> I would argue that there is an abundance of arctic predators that would
> feed upon the geese & their young, including: Arctic fox, Arctic wolves,
> Polar Bears, Grizzlies, Peregrines, Goshawk, mink, Snowy owls, etc.
Then this would seem to be resolvable through data. Which biome has more
potential goose predators, arctic tundra, or other biomes. I don't have
that. I do have a zoology text which gives annual net primary
productivityper unit area for each biome. Tundra is less than a third of
grasslands, and a very small fraction of savannah and all trhe other
biomes except deserts. I suppose you would counter this by saying it is
all in a very short season. But most of the predators you mention must
live there year round. I'll look for actual predator population
figures--in the meantime the same book says migrant diversity is much
higher than resident diversity (it doesn't give population data, though).
> that compared to the first list of temperate predators most of the
> predators in this list are larger in body size, & would be capabe of eating
> a large number of eggs/young/adults, thus having a comparable impact on the
> population as the aforementioned predators. Especially since the temperate
> birds would be better hidden in various plant material. So perhaps the
> supposed adaptation for anorexia & high energy storage allows for larger
> population sizes to accommodate predator saturation.
I agree that predator saturation may well be an important function.
However, I don't think it bears on the argument. It is alot easier to
saturate a few predators than many. Therefore, if I were a goose and I
planned to meet all my geese buddies in vast numbers in order to saturate
predators, I would elect a place with fewer predators so that they would
likely be satiated before they ate me.
> I would also like to point out that Ross's geese & Snow geese do migrate
> into temperate climates during the harsh winters.
Yes. Difficult choices here, perhaps. Do I stay and get killed by the
cold or move and get eaten by predators?
> Being a bird-watcher I
> have had the opportunity to see them as far south as Cincinnati, Ohio.
> They come down, after many of the Canada Geese have migrated south for the
> Winter so that competition is lessened.
Do you mean they are breeding there?