Complex sentence: Effects are not all negative; for example, wind farms produce renewable energy, helping to mitigate the single greatest threat, climate change, but especially if poorly sited, may itself affect bird populations through disturbance, direct or indirect habitat loss, and collisions.
Split into simpler sentences: Effects are not all negative; for example, wind farms produce renewable energy, helping to mitigate the single greatest threat to birds, climate change. But, especially if wind farms are poorly sited, they may affect bird populations through disturbance, direct or indirect habitat loss, and collisions.