Band-rumped Swift
Chaetura spinicaudus
The band-rumped swift is 10.5 to 12.6 cm (4.1 to 5.0 in) long and weighs 13.8 to 18.5 g (0.49 to 0.65 oz). It has a protruding head, a short square tail, and wings that bulge in the middle and somewhat hook at the end. The sexes are alike. Adults of the nominate subspecies have black-brown upperparts with a white band on the rump. Their underparts are dark with a slightly paler throat. Juveniles have white tips on some wing feathers. Subspecies C. s. aetherodroma is smaller than the nominate; its rump patch is grayer and its throat paler. Voice: The nominate subspecies of band-rumped swift "gives a diagnostic bisyllabic 'pseee-trr' or more burry 'prrrree-trtr'" and sometimes also "several repeated notes 'tsee-tsee-tsee'". The vocalizations of subspecies C. s. aetherodroma are not well known.
ID text from Wikipedia, CC BY-SA 4.0
Short-tailed Swift
Chaetura brachyura
The short-tailed swift is about 10.5 cm long, and weighs 20 g. It has long narrow wings, a robust body and a short tail. The sexes are similar. It is mainly black with a pale rump and tail. It can be distinguished from related species in its range, such as the band-rumped swift (C. spinicauda) or the gray-rumped swift (C. cinereiventris) by the lack of contrast between the rump and the tail, the latter being much darker in the other species.
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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Play today's Daily BirdPhotos and recordings are credited to their authors under the licence shown. Full profiles: Band-rumped Swift and Short-tailed Swift.