This would explain their 'laziness " in hot weather ?I think somewhere I read that the Bielefeder was breed to do good with the weather in Estern Westphalia and, trust me, hot weather just does not exist in all of Westpahlia, ..normally. This year we had the hottest summer for over 50 years and it was an disaster for my garden b/c I have no connection to the water line on my allotment, never needed one. I have rain water barrels and til this year it was sufficent b/c normally we have rain every other day.
And I am sorry to hear about all those losses and problems with eggs and chicks. I wish I could help, but my Barbus breed themselfs (I solemnly proclaimed a one chick policy, but some of my hens just don't care and entrench themselves with more than one egg in the box) and I have more chicks than I want to have.... only thing that I do is to move hen and chicks indoor, feed herbal tea and use bird sand not straw or wood chips.
actually, this would explain ALOT, why the birds lack interest in reproduction.
I have cross bred some of mine into my "layer pens" which are birds hardy & just meant to lay nice eggs for my table egg buyers....and the Marans Cock was ON THE JOB over the Biel hens....all the while the Biel cock kinda watched...
In the ned of that last year's marans cock to Biel hen mating, I have now, about 15 cross pullets just at pol...getting about 5 fart eggs a day.
These pullets are 10x more active in forgaing than the pur biels....