USING VITELLOGENIN TO IDENTIFY INTERANNUAL VARIATION IN BREEDING CHRONOLOGY OF MARBLED MURRELETS (BRACHYRAMPHUS MARMORATUS)

Abstract

Vitellogenin is a lipophosphoprotein found in plasma of egg-producing birds prior to laying that may be used to identify fecund females whose reproductive status is otherwise unknown. We captured Marbled Murrelets (Brachyramphus marmoratus) at sea in Desolation Sound, British Columbia, and used vitellogenin to (1) identify variation in egg pro- duction between 1999 and 2000, (2) predict timing of subsequent breeding stages on the basis of egg production, and (3) describe proportion of captured females producing eggs. We also used vitellogenin to investigate a capture bias previously detected in mist-netted birds in the study area and found a corresponding bias in number of egg producers caught. Dates that egg producers were present (27 April to 6 July 1999, 20 April to 6 July 2000) indicate that breeding is highly asynchronous in that species but was similar in both years. Predicted chick-fl edging based on vitellogenin analyses was within one day of fi rst sightings of fl edglings at sea in both years, confi rming that the vitellogenin technique provides accurate information on breeding chronology. Percentage of egg producers (54% in 1999, 56% in 2000) were similar in both years. Vitellogenin analyses provided a chronology very similar to that previously estimated using multiple techniques in the same study area (1996–1998), confi rming that vitellogenin analy- ses alone may be used to describe chronology when sampling encompasses the entire laying period. We recommend that technique for use in other studies of secretive species where egg production cannot normally be monitored by direct observation. Received 3 January 2002, ac- cepted 14 December 2002