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 drongo mimicked alarm calls to steal food from birds like pied babblers and animals such as meerkats. Tom Flower observed that fork-tailed drongos spend a quarter of their time following other animals. Drongos sometimes act as sentries when a predator is approaching, warning their neighbours with genuine alarm calls. But drongos also earn a quarter of their daily calories by sounding a false alarm when another animal finds food. When the meerkats and babblers flee from the non-existent predator, the drongo steals their food. Though in doubt, researchers have considered the possibility that these drongos possess theory of mind, not fully