I doubt that wind turbines are the only power source that kills birds. Marginal bird deaths per unit of power production is the interesting statistic. This MIT post [1] links to a 2009 study [2] which provides that comparison:
4.98 birds/GWh in the fossil fuel estimate comes from unrealized climate change expectations. They also only looked at two coal power plants for the remainder of the study.
The nuclear source bird death estimates are extrapolated from one bad weather incident over two nights from a single plant on the Florida coast.
This is not a serious or rigorous study. Is there anything more recent?
[1]: https://climate.mit.edu/ask-mit/do-wind-turbines-kill-birds
[2]: https://www.sciencedirect.com/science/article/abs/pii/S09601...