  We provide a new efficient diagrammatic tool, in the context of the
scattering equations, for computation of covariant $D$-dimensional tree-level
$n$-point amplitudes with pairs of spinning massive particles using compact
exponential numerators. We discuss how this framework allows non-integer spin
extensions of recurrence relations for amplitudes developed for integer spin.
Our results facilitate the on-going program for generating observables in
classical general relativity from on-shell tree amplitudes through the
Kawai-Lewellen-Tye relations and generalized unitarity.
