The swamp boubou (Laniarius bicolor), also known as the Gabon boubou, is a species of bird in the Malaconotidae or bushshrike family. It is native to western and southern Central Africa. In the north of their range, savannah thickets constitute an important part of their habitat, while in the south they are strongly associated with river systems and marshes, for which they are named. The pair bond appears to be maintained by duetting, which in the south is generally synchronous or overlapping. It is most similar to L. major major, with which it perhaps hybridizes, but the underpart plumage is immaculate white, while the female contributes a ratchet-like note to the duet.
The sexes are similar in appearance. They are large passerines that measure 23 to 25 cm in length. The upperparts are deep blue-black with a slight luster. The long, fluffy rump feathers have concealed white spots, giving the rump a pale appearance. The wings are black with white wing-stripes, and the underparts are pure white. The iris is dark brown, the bill and palate are black, and the legs and feet slate-blue. Juvenile birds have light dusky barring on the underside, and buffy-tipped and barred upperpart plumage. Immatures are duller than adults with buff-tipped wing-coverts and browner bills.
Their larger size, more slender bill, immaculate white underparts, and vocals distinguish them from the tropical boubou where they locally occur together. In those locations the southern race behaves as good species, but somewhat less so with the northern races which are sometimes merged with L. major.