The Lesser Antillean Swift flies over montane forest in the Lesser Antilles. It catches small insects in flight.
Its upperparts are dull brownish gray with a gray rump. The underparts are dark gray and the tail is short.
At the botanic gardens in Dominica, flocks were recorded in the rainy season, flying fast and darting as they caught small flying insects.
It feeds above highland forest in flocks of up to about 40, sometimes visiting lower elevations in bad weather.
It flies with rapid, shallow wingbeats and gives twittering calls.
An extinction-risk assessment has not been added yet.