Why do my house finches leave in October and then return later? They have plenty of food and water. Do they migrate?
House finches are an interesting example of adaptability. The western population of house finches is not migratory. However, birds were transplanted from California to New York in 1940. Since then, from 28 to 54% of individuals marked in this expanding population has displayed migratory movements, according to "Rapid 'Evolution' of Migratory Behaviour in the Introduced House Finch of Eastern North America" by Kenneth P. Able and James R. Belthoff (Proceedings of the Royal Society of London (B), Vol. 265, No. 1410, 1998, pp. 2063-2071). So depending on where you live, they may or may not be migrating. Alternatively, your birds may have just shifted to another local location as preferred food becomes available or weather conditions change.