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 storm petrel finally fledge and leave the burrow. Living in areas with severe climactic conditions, fork-tailed storm petrels have many adaptations to ensure breeding success. Eggs can be left unattended for up to 7 days and still successfully hatch, whereas chick growth rates can be adjusted to being faster or slower depending on food supply, rather at a constant rate like many other birds. The fork-tailed storm petrel is often the sole prey item for a lot of predators early in the breeding season because they return to these remote islands long before any other seabird. These birds consist a significant part