I've been made aware that there is a fictional character named "Valka" and I've been getting questions about whether or not that's where my username comes from.I will need an ark. I will need a reason why the ark wasn't cannibalized for its metal.
I will need a home planet with lots of flying critters. (Altho once they get to their new planet, they will need the ability to fly in perpetuity.)*
I will need lightweight wood, but even bamboo, when it falls, falls down not up.
I will need a reason for this migration...Valka's toxic mists?
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*I'm thinking of a decades-old SF story entitled "With Morning, Comes Mistfall," i.e. with dawn. the planet-wide mist that covered everything receded. If my home world had these mists & if they are Valka's toxic mists, this would explain why the birds have evolved to fly at night instead of nest.
It isn't (and I'd never heard of that other character until recently). "Valka D'Ur" is a name I made up to use as the leader of the Uridian faction in the Lalande scenario of Civilization II: Test of Time. It's a science fiction scenario with a 4-level multilayer map that includes the planet Funestis, orbital platforms, a moon called Naumachia, and a gas giant called Nona. There are 3 alien factions and 4 human factions. The Uridians are one of the human factions.
Getting back to tweaking the genome on your world: It's not enough to do that. You need to account for the planet's existence, period. Take the RL example of Vega. It's been around for far longer than humans have existed, but it's still a very young star. Astronomers have detected proto-planets that might be forming. But Vega doesn't actually have real planets yet. It might not be around long enough before it blows itself up.
This is why I have a really hard time suspending my disbelief when a story comes along with this type of star that supposedly has a planet with life at all, let alone intelligent life. I can forgive storytellers from decades ago because they just didn't know. But nowadays we do know, so what you don't want to do is have a setting that will make anyone who knows basic astronomy immediately say, "Waitaminute, that can't happen."
I'm back pecking away at my Count of Monte Banco novel tonight. But there's no rhythm, no magic. I can hear Truman Capote declaring, "That's not writing. That's typing." 
I spent the day not writing qua writing, but rather going back and filling in plot holes. Those had been bothering me since forever. I feel much better now. 
A novel without an outline is like a ship without a rudder or charts.
If the ending seems rushed, I'll worry about it then.
Yet calcium is needed for everything from bones to heartbeats. Clearly, I need to come up with some eco-mechanism that brings calcium into the food chain. 
