Age-specific breeding probability in black brant: effects of population density

1. We estimated age-specific probability of breeding for black brant (Brant a bernicla nigricans Lawrence) (hereafter brant) at the Tutakoke River Colo ny, Alaska, during a series of years in which local breeding density and ju venile mortality both increased. We use these analyses to examine demograph ic responses to increased population density. 2. Estimates of breeding probability were based on Kendall & Nichols (1995) full-likelihood modification of Pollock's (1982) robust design applied to observations of uniquely colour-banded brant. 3. Breeding probability varied with female age but not across years, indica ting lack of response to increased population density. Annual probability o f breeding increased from 0.67 +/- 0.042 for 2-year-old females to 0.90 +/- 0.024 for females 5 years old or older. 4. Annual breeding probability of males greater than or equal to5 years old was 0.78 +/- 0.03. Lower breeding probability of males compared to females probably reflects dispersal of males whose mates died. 5. Lower juvenile survival appears to be a general response to increased de nsity in large herbivorous birds and mammals, while changes in adult surviv al and reproductive investment may be more variable.