  Entanglement between blocks of energy-levels is analysed for systems
exhibiting s-wave and p-wave superconductivity. We study the entanglement
entropy and spectrum of a block of $\ell$ levels around the Fermi point, and
also between particles and holes, in the ground state of Richardson-type
Hamiltonians. The maximal entropy grows with the number of levels $L$
approximately as $1/2\log(L)$, as suggested by the permutational symmetry of
the state at large coupling. The number of levels in the block around the Fermi
surface with maximal entanglement is proposed as a measure of the number of
{\em active Cooper pairs}, which correlates with standard estimates of this
magnitude. The entanglement spectrum is always composed of a principal
parabolic band plus {\em higher bands} whose disappearance signals a exact BCS
state, e.g. in the Moore-Read line, while the Read-Green quantum phase
transition is characterized by a maximum in their weight.
