... those with less than 50 reported an average loss of 15%...
...Hives kept in towns averaged 22% winter loss...
<I believe these numbers are related to beekeeping skills.>

Peter,
I agree with your conjecture, based on my observations of the hobby beekeeper community here in the Puget Sound region of Washington, if such can be generalized to Europe.  Last year the Puget Sound Beekeepers' Association (PSBA) hosted a presentation of  results of a research project conducted by Danny Najera, PhD, a PSBA trustee who's a biology instructor at one of the local community colleges who runs a beekeeping program in conjunction with his classes.

Danny's research project was a response to feedback from PSBA members concerning winter hive losses.  He set up a monitoring program of 100 hives throughout the area volunteered by their owners, and he used his students to help with the data gathering. They equipped the hives with temp&humidity monitoring equipment, and gathered data on hive weight, mite counts, and not sure what else.  They were very systematic with the data gathering.  One of the concerns of the local beekeepers was to what degree the heavy winter dampness of Pacific Northwest winters was contributing to hive mortality.  Danny's data analysis suggested that by far, the biggest reason for winter hive mortality was mites.  The most interesting data set was the mapping of where the dead hives were: the greater proportion of them were in the lowland urban areas - where winter temps are less extreme, but hive locations in closer proximity... close enough that cross-contamination from robbing is an issue. Most of these urban beeks are hobbyists, some of whom will not treat their hives or don't treat them adequately. Even those of us who do treat have to be more vigilant because of the treatment-free "fanatics". 

Here in the city we have so many hobby beeks that we might actually be somewhere near the saturation point for what forage is available, too. This points out another aspect of beekeeping that hobbyists fall down on - adequate fall prep and winter feeding.  I don't know if Danny Najera is going to publish a paper on his research, but anyone interested in this study could contact him by visiting the website below; his email address is on that page.

https://www.greenrivercollegefoundation.org/greenriverhoneybees

Mary Ann Kae (4th year hobby beek)
Seattle, WA

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