The Relation of Castration to Migration in Birds

ORN•r•OLOG•STS have long been interested in the basis of the physiological cycle which causes the nfigration of birds. On account of the close correlation between the seasons of migration and the variation in the size of the reproductive organs, it has been believed commonly that the reproductive organs control the cycle.This belief was shared by Chapman (1894), Wetmore (1920), Bergtold (1926), and Schildmacher (1933), but the theory was questioned by Sch•fer as early as 1907, and by Phillips in 1913.Both Phillips and Bergtold suggested experiments in castration as a possible method of settling the question, but both thought such experiments impracticable.Rowan (1932), however, in the autumn of 1931, castrated and liberated several male crows, but treated all except three by injecting hormones, which disqualified them for the present problem.All three of the untreated crows were recovered after migrating in the usual southeasterly direction, indicating, as Rowan exi)ressed it, that "• hatever may be the case with the northward migration, the southward is evidently not associated with the state of the reproductive organs."Putzig (1937) also reported that a Lesser Black-backed Gull (Laru•' fuscus) and two Black-headed Gulls (Larus ridibundus) which were castrated at Rossiten, Germany, were later recovered in southern Europe on the fall migration route.Early in the year 1933, the writer began some experiments in the relation of castration to the migration of birds in connection with a banding station at Saginaw Forest five miles west of Ann Arbor.The results, though not as decisive as hoped for, are reported at this time, because the banding station has been discontinued, and there is little likelihood that any remaining birds will be recovered.Three species of birds were used, Slate-colored Juneos (Junco h.hyeraalis) (winter residents or migrants), Red-eyed Towhees (Pipilo e. erythrophthalraus) (summer residents or migrants), and White throated Sparrows (Zonotrichia albicollis) (migrants).The juneos,three in number, were operated on in April; five towhees in September and October; and the White-throated Sparrows, twenty in April and May during spring migration, and nine in October and early November during fall migration.'Only males were used, as testes were less difficult to remove with certainty than ovaries.Birds were operated on under anesthesia, and were released near where they were trapped, usually on the day following the operation.The immediate results of the operations were that most of the birds remained around the station, entering the traps more or less