Notes on Fall-Hatched Tricolored Blackbirds

Notes on fall-hatched Tricolored Blackbirds.--In October, 1959, at least two large colonies of Tricolored Blackbirds (Agelaius tricolor) bred in rice-growing districts in the Sacramento Valley of California (for details see Orians, Auk, 77: 379-398, 1960). This note reports the data on molt and gonadal cycles in 12 nestlings taken from nests during the first two weeks of November and handreared. The birds were kept in buildings, where they were subjected to some nighttime disturbance until mid-December, when the 10 surviving individuals were transferred to an aviary in Strawberry Canyon on the campus of the University of California at Berkeley. Thereafter all birds experienced natural photoperiods. The research reported here was conducted under the supervision of F. A. Pitelka while I was the recipient of a National Science Foundation Graduate Fellowship. Help with the initial laparotomies was generously given by A. H. Miller. All birds began their postjuvenal molt in late December, completing it by early February. Thus, the postjuvenal molt followed fledging in the normal manner despite drastically altered temperatures and photoperiods. The second week in February several of the males began to sing abnormal songs, analysis of which will be given elsewhere. On 12 May 1960 laparotomies were performed on all birds. Three of the four males had greatly enlarged testes and five of the six females had enlarged ova, typical of the stage to be expected in wild females just prior to initiation of nest building (Table 1). The remaining female was extremely emaciated and died as a result of the operation. Inactive testes in male Tricolored Blackbirds are usually less than two mm in length, and the mean value of testis length in 41 adult males shot from the fall breeding population in October was 6.3 mm. Therefore, it is likely that the hand-reared males were in potential breeding condition at this time.