Before autumn departure a ruby-throated hummingbird lays down subcutaneous fat, commonly climbing from about three grams to five grams or more. Fat is the densest fuel a bird can carry, and at those small body sizes the stored energy is enough for a sustained flight of many hours.
Banding and radar work indicate that a substantial share of the population crosses the Gulf directly, a distance on the order of 800 kilometres, while others follow the Texas and Mexican coastline overland. Both routes are genuine; the crossing is not obligatory for every individual, and weather at departure strongly influences which is taken.
The long-running claim that hummingbirds ride on the backs of geese has no evidence behind it and conflicts with the two species' different migration timing and routes. What remains genuinely unresolved is the proportion of birds that cross open water in any given year, and how often a crossing fails.