Our first bee colony loss

We have been keeping bees for 4 years now and have slowly increased to 4 hives, but this winter we lost one.  We last checked the hives only two weeks ago and they were still alive then but we did not go right into the brood box to check so number must have been very low and we did notice they were not eating much of the fondant we had given them. Anyway, as this picture shows it is now a very empty box with dead bees in the corners. Looking back I realise that it was not a strong colony when winter started; we had merged two mediocre colonies which had both had bad summers, swarming multiple times and having periods of queenlessness. 

I remember reading somewhere that two weak colonies will not make one strong one but it seems illogical becuase you are making one bigger colony in terms of pure bee numbers but I guess there is some other factor involved with the colonies organisation structure.

Anyway, its been a terribly long winter and I guess, in the circumstances, these losses are to be expected. Its still a little upsetting though.  Lets hope for a good summer (if it ever arrives) that will enable us to replace this colony. We need a couple more hives now as we have two sites.