Sabine's gull treated as comprising a monotypic genus; it is only placed within the genus "Larus" when the genus is enlarged. The black bill and notched tail are almost unique within the gulls, as they are shared only with the swallow-tailed gull of the Galapagos. On the basis of this the two species were often thought to be each other's closest relatives, a hypothesis ruled out by a number of behaviour and ecological differences. Mitochondrial DNA studies confirmed that they are not closely related, and the closest relative of the Sabine's gull is now thought to be the ivory gull, another Arctic
Fork-tailed flycatcher and Canada. This flycatcher builds a shallow cup nest high in a shrub or short tree. Females normally lay two or three eggs. The fork-tailed flycatcher is white below, gray above, and has a black cap. Males sometimes show a yellow crown stripe. Males also have an extremely long forked tail, of even greater length than that of their cousin, the scissor-tailed flycatcher. Females have a somewhat shorter tail, while it is significantly shorter in juveniles. Males are in length; females, , including tail. They weigh only , much less than closely related kingbirds, which are half the total length