Farewell Spit provides a wide variety of habitat for birds, including ocean sand beaches, bare and vegetated sand dunes, salt marshes, and lakes both freshwater and brackish. The dunes at the end of the spit support the only sea-level colony of
Australasian gannets in the world. The eelgrass (
Zostera) beds on the tidal flats are used by the largest moulting population of
black swans in New Zealand. In 2014, an area of at Farewell Spit was recognised as an
Important Bird and Biodiversity Area (IBA) by
BirdLife International.
Shorebirds A study of shorebirds in the top of the South Island, commissioned by the
Nelson City and
Tasman District councils, was published in 2013. This study reported that from 2006 to 2009, the population of coastal shorebirds found in the estuaries in the top of the South Island represented between 14 and 22% of the total New Zealand shorebird population. Over the period of one year, between 45% and 66% of shorebirds in the study region were found at Farewell Spit. During summer, there is an average of about 29,000 shorebirds at Farewell Spit, representing 10.2% of the national population. During winter (June), there is an average of 8,500 birds, representing 6.5% of the national population, and in spring (November) there is an average of 20,000, representing 13.2% of the national population. Farewell Spit typically has more than 20,000 shorebirds present during summer and spring, and this meets the criteria for recognition under Ramsar Convention Criterion 5 as a wetland site of international importance. During spring and summer, migratory waders make up a large proportion of the shorebirds at Farewell Spit (up to 93% during spring). Farewell Spit is a site of international importance for migratory bar-tailed godwits. Surveys have found an average of 11,872 godwits are present in the summer period, representing 9.1% of the total estimated numbers of this species in the flyway. Farewell Spit is also of international importance for shorebirds such as the South Island pied oyster-catcher. Surveys have found an average of 6,980 of these birds during summer, representing 7% of the estimated national population. The spit is also an important wintering area and a site of international importance for the banded dotterel.
Australasian gannets A breeding colony of Australasian gannets was identified at Farewell Spit in 1983. The size of the colony increased from 75 nests in 1983 to 3,060 nests in 2001, and a 2006 survey recorded 3,300 pairs. The breeding area comprises several discrete sub-colonies at the end of the spit, around 30 minutes walk past the lighthouse. The breeding colonies are only a few metres above sea level, and this is unusual because gannet colonies are usually well above sea level on high, stable rock formations. In 2022, there were 10,000 birds in the colony.
Other seabirds Other seabirds that nest on shellbanks on Farewell Spit include
Caspian terns and
white-fronted terns.
Waterfowl Farewell Spit has been identified as the largest moulting site for
black swans in the country, with up to 15% of the total population present between November and March. Significant numbers of
Australasian shoveler have also been reported. ==Conservation initiatives==