We analyzed capture-mark-recapture (CMR) data from 1,061 Black Brant (Branta bernicla nigricans) using Humboldt Bay, California, during northward migration (Jan–May), 2000–2001. We estimated immigration and emigration rates, and calculated stopover duration (length of stay), volume (total number of birds using the Bay), and chronology (time frame of the migration at this site). Migration of Brant through Humboldt Bay began in late December and ended in mid-May with peak numbers occurring in mid-March (i.e., 13% of the entire flyway population). Median age of newly arrived birds was highest in the first half of February. Immigration probability was nearly constant, but emigration probability increased through time, indicating a seasonally progressive migratory state. Mean (±SE) stopover duration from all birds for January–April at Humboldt Bay was 26 ± 2 days. Stopover duration was inversely related to bird age due to age-specific emigration probabilities; older birds arrived sooner and stayed for less time than younger birds. Estimates of stopover duration from concurrent radiotelemetry of 12 birds were consistent with CMR model selection-derived estimates. Humboldt Bay was visited by approximately 28% of the Pacific Flyway Black Brant population in 2000 and 58% in 2001. Estimates derived from this technique offer statutory authorities improved information upon which to base management action along migratory pathways.
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