Crithagra concolor, or the São Tomé grosbeak, is endemic to the island of São Tomé in the Gulf of Guinea. It is one of the least known birds in the world and the largest known species of canary. Before being assigned to the canary genus Crithagra, it was erroneously placed in the genus Neospiza (meaning “new finch”). After a phylogenetic analysis of mitochondrial and nuclear DNA sequences, the São Tomé grosbeak was reclassified. 

Its bill has been described as massive, considered atypical for its species. It is also quite substantial in mass, weighing on average 50% more than the next heaviest species of canary. The São Tomé grosbeak went unsighted for nearly 100 years before being ‘rediscovered’ in 1991. The IUCN classifies the species as critically endangered, with an estimated population of less than 250 birds.

references:

1. BirdLife International (2018). ”Crithagra concolor”. IUCN Red List of Threatened Species.

2. Sekar, Sandhya (5 April 2017). “World’s largest canary discovered on island of giants and dwarfs”. New Scientist.

3. Melo, Martim; Stervander, Martin; Hansson, Bengt; Jones, Peter J. (2017-07-01). “The endangered São Tomé Grosbeak Neospiza concolor is the world’s largest canary”. Ibis. 159 (3): 673–679.

4. Gill, Frank; Donsker, David (eds.). “Finches, euphonias”. World Bird List Version 5.2. International Ornithologists’ Union.