Green’s Dictionary of Slang

1. (US) an impoverished tramp who enlists in the forces as the winter arrives in order to get food and shelter for the next few months, then deserts when the warmer weather returns.

1899–1900		C.L. Cullen Tales of the Ex-Tanks 198: They [i.e. sailors] were all loaded for snowbirds.
1905		N.Y. Eve. Post 20 Nov. 6: 28 Per cent. deserted after three months, and were presumably ‘snow-birds,’ that is, men who enlist to get food and clothing during the winter months [DA].
1923		Nation 31 Oct. 487: In winter, when building is at a standstill in the North, northern workmen, ‘snow birds’ or ‘white doves’ in Negro parlance, flock south [DA].

2. (US, Florida and other Southern states) a winter tourist who travels south to avoid the chilly weather.

1924		‘Digit’ Confessions of a Twentieth Century Hobo 12: Snowbird... (2) In the Southern States a Northerner who migrates south to avoid the winter. [Ibid.] 68: You doggone snowbirds, beat it while the going’s good.
1986		C. Hiaasen Tourist Season (1987) 29: He was [...] jolliest when Florida was crawling with snowbirds.
1995		J. Stahl Permanent Midnight 277: Those who come [to Arizona] just to pass the flu season are known as ‘snowbirds.’.
2004		R. Romano at lasvegas.about.com 🌐 The ‘snowbirds’ are coming! The seniors and warm weather followers are putting supplies into their motor homes to last them until April or May. It’s time to get out of the snow belt and into Las Vegas or Southern Nevada.
2005		L. Theroux Call of the Weird (2006) 15: RV parks populated by the flock of itinerant elderly known as ‘snowbirds’.

3. (US tramp) a tramp who goes south for the winter.

1930		J. Tully Shadows of Men 81: What’s the matter, Husky, old snowbird.
1949		Monteleone Criminal Sl. (rev. edn).
2000		W.T. Vollmann Royal Family 734: It’s hard to find any trees to live under. Them snowbirds are already in the good spots.

4. a fan of winter weather and/or winter sports.

1916		O.O. McIntyre New York Day by Day 22 Mar. [synd. col.] ‘Snow Birds’ is the popular name for those winter bathers whom you see plunging into the surf at Coney Island in midwinter.
1918		A.N. Depew Gunner Depew 234: It is all right to be a Coney Island snowbird and pose around in your bathing suit in the drifts.