300 SNODGRASS AND HELLER 



where. From Tagus Cove we have twenty two specimens of males 

 taken in January, two taken in February and fourteen taken in March. 



All of the clearly immature birds occur in the January and February 

 lot. Most of the January specimens are in the brown plumage, 

 Stage III, four are in Stage IV and two in Stage II. Both of the 

 February specimens are in Stage V. Nearly all of the March speci- 

 mens are in Stage VI or in a condition intermediate between Stage V 

 and Stage VI. This is the typical breeding plumage. One specimen, 

 however, is in Stage V and was taken apparently mated with a 

 female. Another specimen taken mated with a female is actually in 

 Stage III ! This, then, shows that, although the black or nearly black 

 plumage and sexual maturity generally coincide, yet the melanistic 

 phase may be retarded. It is also evident that the ?nales do not be- 

 come entirely dusky until the end of the first year. 



All the March males have the bill perfectly black. Few of the 

 others, however, have the bill entirely black, most of them having 

 some remnant of the yellow on the lower mandible, either as a definite 

 spot near the tip of the gonys or as a diffusion over the base. Some 

 even with purely black plumage have the lower mandible entirely 

 yellow. Hence the bill does not become entirely black until the end 

 of the first year and may remain partly pale longer than the 

 plumage. The breeding male in plumage Stage III has the bill 

 entirely black, thus resembling exactly the adult female. Hence, 

 sexually mature males may have immature plumage, but we have no 

 case of a breeding bird having an immature bill. 



From Iguana Cove we have sixteen male specimens taken in Janu- 

 ary and two taken in March. 



Of the January birds only four are in Stage VI, eight are in Stage 

 V and IV or intermediate between the two, and three are in Stage III. 

 Yet all of these birds except one (this one in Stage III) were ap- 

 parently breeding males. The nesting season had here begun at this 

 season and the males in all stages of plumage had the testes enlarged 

 as if breeding. The breeding season at Iguana Cove begins about two 

 months in advance of that at Tagus Cove. This difference is due most 

 probably to the much greater humidity of Iguana Cove as compared 

 with Tagus Cove. The breeding season lasts at least as long as it 

 does at Tagus Cove, i. c, until April. Hence, it is probable that 

 birds hatched here during the last of a season begin breeding at the first 

 of the season in the following year when they are only ten months old, 

 being in Stage V or even IV, and, hence, before they have had time 

 to acquire the full black plumage. 



