Another chick died, 8 chicks left

Sadly, another chick has died. Why this happened is not clear to me because all chicks looked healthy and active not long before. And although some chicks are older and more developed than others, none of them seemed really far behind.

Yesterday evening when I counted only 8 chicks for more than an hour, I became worried and checked video footage from the previous hour and searched for the last moments that I could still see 9 chicks. Here is that footage (I have cut out about 2 minutes in the middle). You can see one chick in upper right corner that is much weaker than the rest. It doesn't raise his head for food anymore and after this video I never saw it alive again.

Chick is dying, 4 May 2014 5:51pm

The next morning (today) I saw the mother find the dead chick and removing it from the nest.

Mother removes dead chick from the nest, 5 may 2014 6:56am

On a positive note, one chick less improves the chances of survival for the remaining 8 chicks.