  Using angle-resolved photoemission spectroscopy, we study the evolution of
the number of carriers in Ba(Fe(1-x)Cox)2As2 as a function of Co content and
temperature. We show that there is a k-dependent energy shift compared to
density functional calculations, which is large at low Co contents and low
temperatures and reduces the volume of hole and electron pockets by a factor 2.
This k-shift becomes negligible at high Co content and could be due to
interband charge or spin fluctuations. We further reveal that the bands shift
with temperature, changing significantly the number of carriers they contain
(up to 50%). We explain this evolution by thermal excitations of carriers among
the narrow bands, possibly combined with a temperature evolution of the
k-dependent fluctuations.
