Molt of Black Brant (Branta bernicla nigricans) on the Arctic Coastal Plain, Alaska

I examined patterns and chronology of the prebasic molt and primary-feather growth rate of nonbreeding and postbreeding Black Brant (Branta bernicla nigricans) on the Arctic Coastal Plain, Alaska. I estimated molt intensity for adults and subadults of both sexes with molt rate (MR, proportion of feathers in blood quills) and percent new feathers (PN, proportion of feathers that recently completed growth) for 26 feather tracts. I then calculated mean total molt score (TMS) and mean total percent new score (TPN) for each sex, age class, molt stage (arrival, start, early, mid-, and late molt), and Julian date. TMS increased from arrival to early molt (14 June-22 July). Subadults molted at greater intensity than did adults during early, mid- and late molt (20 July-1 August); however, males and females in both age classes did not differ. TPN scores were significantly (P < 0.05) greater from 25 July to 1 August than from 20 to 22 July, primarily as a result of maturation of remiges and wing coverts. Brant replaced body and wing feathers concurrently. Back, rump, breast, and side regions were comprised of 25% or more blood quills in adults to 50% or more blood quills in subadults during the nightless period. Brant departing the molt area completed growth of only 11 to 21% of all feathers. Ninth-primary growth rate ((x) over bar = 7.2 +/- SE of 0.1 mm/day) did not vary over sex and age classes nor between years (1988 vs. 1989). Remex growth rate declined significantly (P < 0.001) through molt but was not related to Julian date nor initial body mass. Most Black Brant began remex growth 4-10 July; however, some postbreeding adults did not arrive and start molt until 24-25 July. Brant made short nights when the ninth primary averaged 62% of its mean final length; sustained night occurred at about 70% of completed growth. The duration of flightlessness was 23 and 24 days for females and males, respectively. Flightless Black Brant were present in the Teshekpuk Lake molting area from 26 lune through 19 August. Upon regaining flight ability, Black Brant moved to coastal staging areas. The chronology and intensity of feather replacement for Black Brant may be important when determining the appropriate management of habitats where molt occurs, especially when these are disturbed by human activities.