The rotors turn slow in terms of rpm but fast in terms of wingtip speed, due to the very large radius. But many things kill birds, I do not believe that wind turbines could ever make much of a difference.
Unless I'm miscalculating, that means that the tip of one of the rotors will travel 515 metres per revolution, which at 4.8-12.1rpm is a tip speed of between 2,472 metres per minute and 6,231 metres per minute.
To put that in more common units, that's between 148km/h and 373km/h.
[1] https://stateofgreen.com/en/profiles/vestas/solutions/v164-8...
Second benefit of larger turbines is much more of the swept area is outside of the normal flight heights of birds. Either too low for migration patterns or too high for most hunting and scooting flight heights (relative to nearest surface).
So one 8MW turbine is likely to kill a lot less than 8 * 1 MW and much, much less than 80 * 100kw, even if it has a much larger swept area.
Now as these are offshore turbines, and Hywind, being for quite deep water. Likely to be far offshore, there are not that many birds around too get hit in the first place.
The nice thing about the slower RPMs compared to smaller tubines (especially pre 2000's) is that slower RPM's make it easier to spot the turbine for birds. High RPM's give optical effects that make it hard to predict where something is going (e.g. wheel looks like rotating backwards etc...) so bigger is easier too avoid for birds.
[1] http://www.audubon.org/news/will-wind-turbines-ever-be-safe-...
After accounting for initial setup costs and maintenance of wind turbines (it is worse than Solar in this regard because of the wear and tear in mechanical parts) and power infrastructure (which has to be designed to handle such variation without any impact on consumers), it will take a very long time to break even, if at all. And don't forget that we will still need something reliable like nuclear or fossil fuels to back it up... which we already have enough of to last for thousands of years.
So, basically, all we get with wind is more work for no gain at all (not to mention the unnecessary environmental harm). I am sure Statoil is not ignorant of this. They are just using a small portion of their 100 billion dollar yearly revenue in this to please the eco-terrorists.