We used four methods to compare the breeding chronologies of Marbled Murrelet at two sites at similar latitudes in British Columbia: Desolation Sound on the mainland, inshore of the Strait of Georgia, and Clayoquot Sound on the west coast of Vancouver Island. At both sites, we estimated breeding chronologies from the timing of (1) nest initiation dates determined by radio-telemetry, (2) the chick feeding period determined from observations of fish-holding adults, (3) hatch dates determined from observations of juveniles on the water, and (4) brood patch scores determined from captured birds. At Desolation Sound, these methods each produced a similar distribution of nesting dates, but at Clayoquot Sound, the distribution of nesting dates of radio-tracked birds were substantially biased towards later nests. Despite these methodological difficulties, we found that Marbled Murrelets at Desolation Sound bred ca. 30 d later than at Clayoquot Sound. Regional differences in breeding chronology of this magnitude, if not properly calibrated, would bias estimates of peak inland activity, and should be considered in forestry operations, the interpretation of census data, and the design of monitoring programs.