Grote, H. 1924. Hirundo griseopyga gertrudis n. subsp. Ornithologische Monatsberichte 32.3: 72.
Zwergform: Flügellänge von vier adulten und einem semiad. Vogel (alle vom Benüe) 88-93 (88 - 88 - 88.5 - 91 - 93) mm gegen 96-101 mm bei der Nominatform (Exemplare aus Ostafrika). Typus im Zoolog. Museum Berlin. f. ad., Benüe bei Garua (Adamaua), 31.VII.1909, Riggenbach leg. Nr. 980. Auge "blau," Schnabel "schwarz," Füsee "schwarzbraun." Als Synonyme zur Nominatform sind nach Reichenow (Vög.Afr. II, p. 403) anzusehen: "Atticora melbina Verr." [Gabun], "Atticora cypseloides Heugl." [Abessinien] und "Hirundo poucheti Petit" [Kongo]. Mir liegt aus den gennanten Gegenden kein Stuck vor, aber Mr. Norman Kinnear (London) hatte die Freundlichkeit, auf meine Bitte hin das diesbezügliche Material des British Museum durchzusehen. Er fand folgende Flügelmasse: Exmpl. von Gabun (Duchaillu leg.): 100 mm, Expl. von Mayumba (Kongo): 99 mm, Expl. von Guatti (Abessinien): 96 mm. Es handelt sich demnach durchweg um langflügelige Vögel, deren Flügellängen in die Flügelvariationsbreite der Nominatform fallen.
Very small form: wing length of four adult and one subadult bird (all from Benue) 88-93 (88 - 88 - 88.5 - 91 - 93) mm, as opposed to 96-101 mm in the nominate form (specimens from east Africa). Type in the Zoological Museum, Berlin: adult female, Benue, near Garua (Adamaua), July 31, 1909, coll. Riggenbach Nr. 980. Eye "blue," bill "black," feet "blackish brown." According to Reichenow (Vög.Afr. II, p. 403), the following should be considered synonyms of the nominate form: "Atticora melbina Verr." [Gabon], "Atticora cypseloides Heugl." [Abyssinia] and "Hirundo poucheti Petit" [Congo]. No specimen from those areas is available to me, but Mr. Norman Kinnear (London) was so kind as to review the relevant specimen material of the British Museum on my request. He found the following wing measurements: specimen from Gabon (coll. Duchaillu): 100 mm, specimen from Mayumba (Congo): 99 mm, specimen from Guatti (Abyssinia): 96 mm. Thus these are all decidedly long-winged birds, and their wing lengths fall into the range of variation exhibited by the nominate form.