Justification of Red List Category
This species has a very large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be increasing, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
The overall population trend is increasing, although some subpopulations have unknown trends (Delany and Scott 2006).
This species can be found at both coastal and inland locations in a variety of habitats including artificial habitats such as rubbish dumps. It has a very varied, opportunistic diet including fish, marine and terrestrial invertebrates, seeds, insects and bird eggs. Kleptoparasitism has been observed. It breeds on small islands and points, mainly offshore, but also on freshwater and brackish lakes, and on causeways in salt-pans. The breeding season covers all months, with the exact timing varying depending on locality and age. It is colonial and occasionally solitary, with smaller colonies in the tropics (3-25 pairs) up to 3,000 pairs in southern Australia. Colony size depends on food availability. Individuals may wander widely outside the breeding season (del Hoyo et al. 1996).
L. n. scopulinus can be found on coasts, lakes, rubbish dumps, sewage outfalls, fishing piers, wet lawns and fields. It feeds mainly on euphausiid krill and other planktonic crustaceans in the breeding season, but also earthworms, insects and small fish. Outside the breeding season its diet is more variable, including fish, refuse and berries. It is also commonly a kleptoparasite. It begins nesting in July, laying between late September and December. Colonies can be very dense on the main islands, but small groups or even solitary birds are found on subantarctic islands, and can be found on rocky beaches, islands and stacks, and rarely on inland lakes. Almost all birds return to their natal colonies and retain mates from year to year. Birds returning early take large, central territories in the colony which are defended for a large period. After the breeding season most birds remain within 380 km of the colony, though juveniles may travel further (del Hoyo et al. 1996).
This species is facing threats from multiple invasive alien species. In New Zealand, stoats Mustela erminea are significant egg predators, cats Felis catus are identified as contributing to the population declines and rats Rattus spp. are identified as contributing to the declines noted at the three largest colonies in the country (Mills 2013).
Text account compilers
Ekstrom, J., Martin, R., Butchart, S., Stuart, A., Symes, A., Taylor, J., Calvert, R.
BirdLife International (2023) Species factsheet: Larus novaehollandiae. Downloaded from http://datazone.birdlife.org/species/factsheet/silver-gull-larus-novaehollandiae on 28/05/2023. Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://datazone.birdlife.org on 28/05/2023.