All science is provisional until years or decades of continuing analysis and experimentation results in a widespread consensus. The article provides a peer reviewed analysis which had passed muster in a reputable scientific publication.There is a reason this Abstract is at the beginning of your link.
"This article explores the threats that wind farms pose to birds and bats before briefly surveying the recent literature on avian mortality and summarizing some of the problems with it. Based on operating performance in the United States and Europe, this study offers an approximate calculation for the number of birds killed per kWh generated for wind electricity, fossil-fuel, and nuclear power systems. The study estimates that wind farms and nuclear power stations are responsible each for between 0.3 and 0.4 fatalities per gigawatt-hour (GWh) of electricity while fossil-fueled power stations are responsible for about 5.2 fatalities per GWh. While this paper should be respected as a preliminary assessment, the estimate means that wind farms killed approximately seven thousand birds in the United States in 2006 but nuclear plants killed about 327,000 and fossil-fueled power plants 14.5 million. The paper concludes that further study is needed, but also that fossil-fueled power stations appear to pose a much greater threat to avian wildlife than wind and nuclear power technologies."
This paper was written in 2009 when Wind was still at its infancy. Wind accounted for 73.9 TWh per year power in the U.S., Nuclear 798.9 TWh per year and Fossil Fuels 2726.5 TWh per year. As you can clearly see the paper does not take into account the
proportional disparity in energy sources. So, if you put Wind into the Nuclear and Fossil Fuel equivalent, Wind would be responsible for 2.9 Avian Deaths per GWh, and 191.1 Avian deaths per GWh. As you can clearly see much, much higher than Nuclear or Fossil Fuels. Wind is not even close for safety.
Here is a 2013 study that provides the same conclusion: compared to fossil fuels and nuclear, wind farms are vastly more safe for avian wildlife and bats. By a country mile.
The Avian and Wildlife Costs of Fossil Fuels and Nuclear Power
Journal of Integrative Environmental Sciences vol. 9, no. 4, December 2012, 255-278 (June 2013)
Within the uncertainties of the data used, the estimate means that wind farm-related avian fatalities equated to approximately 46,000 birds in the United States in 2009, but nuclear power plants killed about 460,000 and fossil-fueled power plants 24 million.
https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2198024