The decision is simple you are either saving the lives of coutless birds, or you are greatly decreasing CO2 output.
Arguably, the CO2 decrease is better. For one, it retards Global Warming which is better for everyone. Secondly, smog from coal burning facilities will be lessened with the availablility of cleaner power.
While the windmills will decrease overall pollution, there is a problem. They take up a LOT of land. Those massive fans can dot fields for mile. In order to get all this land, trees and other wildlife would need to be removed.
So you're either saying
"I want a cleaner planet riddled with windmills and dead birds"
"I want to save the animals while also smogging up the atmosphere and increasing global warming!"
Personally, I think those are the options with any sort of clean power.
Solar panels take up land and are unreliable, Dams disrupt aquatic wildlife, windmills kill birds and take up more land.
There is no right solution to this question. It is really just a matter of morals belief.
I am an environmentalist BUT I am a pro-human environmentalist. I say we care about and take care of the environment for the sake of human beings. Coal and oil power plants pollute the air and compromise human health, and contribute to global warming which threatens human beings. If some more birds have to die so the air can be clean for humans so be it.
It's just stupid to use fossil fuels when there are far better renewable and ecologically friendly materials available. Not to mention if we continue to release vast quantities of CO2, there will eventually be no birds anyway - or other forms of life. Apart from that, why do the two have to be mutually exclusive? Solar doesn't harm birds, nor does hydro. And surely someone can come up with a way to keep birds away from wind turbines? Sounds to me like a red herring probably introduced by the fossil fuel lobby.
Animals aren't stupid. A few birds will die, but after a few months or years the survivors will wise up and learn to not go to that area again. Who really cares about a few hundred birds anyway? It's not like a few wind farms are going to completely kill off entire species of birds. A few hundred or thousand animal sacrifices for humans. That already happens. Why is this any different?
I understand why some people are concerned about the safety of birds, but I believe that this source of energy is far less dangerous for them than fossil fuel is (just think about the major spilling in the oceans). However, I believe that nuclear energy would be a better solution.
This all should depend on whether birds have feelings. As Bentham said "the question is not Can they reason? Nor Can they talk? But Can they feel?" While he was considering slaves the sentiment remains the same. If they can feel pleasure or pain then we should not head them towards pain that is the action of a monster. Most adopt an anthropocentric view that is to say that all beings and all nature are here as instrument to man but this is not true. Even more what right have we to end the lives of these birds? There is no moral superiority these are not killer birds or nazi birds but birds that live and breath. If there is a more peaceful alternative it is our duty to take it.
This all is not to say that maybe other energy sources are maybe even morally worse however that would not answer the question.
Yes, pursue clean energy via windmills, but that doesn't mean that concerns about birds should be dropped. That's an either/or fallacy. Anyway, as far as I'm aware, sound-wave technology is being developed to deter birds from dangerous equipment. We don't need to stop developing it. If birds go extinct, we will notice it. There'll be more gross bugs in our houses, for instance. The food chain must maintain balance :P