Distribution, Abundance and Population Trends of the Kittlitz's Murrelet Brachyramphus Brevirostris in Prince William Sound, Alaska

Abstract

Monitoring population trends of rare species can be difficult if they cannot be readily separated from closely related, abundant species . Such species identification problems affect monitoring in Prince William Sound (PWS), Alaska, where Kittlitz’s Murrelets Brachyramphus brevirostris co-exist with Marbled Murrelets B. marmoratus . We examined murrelet trends using data from PWS-wide surveys conducted in 11 years between 1972 and 2007, and models that incorporated murrelets not identified to species in population estimates . We examined modeled trends with and without unusually high (1972, 1993) or low (1998) population estimates . In 2001 and 2009, we also conducted intensive surveys for Kittlitz’s Murrelets . Based on field estimates, identified Kittlitz’s Murrelets declined by 63% (5% per annum) between 1989 and 2004 but appeared stable thereafter . Model estimates that incorporated unidentified birds suggested a steeper decline of 13% per annum between 1989 and 2007, and negative trends were obtained regardless of which years were included . Marbled Murrelets showed a lower rate of decline in modeled estimates, but field estimates for identified Marbled Murrelets continued to decline after 2004 . Intensive surveys for Kittlitz’s Murrelets produced a higher population estimate in 2009 than in 2001 . Recent estimates for Kittlitz’s Murrelet were 2346 birds (95% CI 514–4178) from the PWS-wide surveys in 2007, and 2080 birds (1409–2990) from the intensive surveys in 2009 . We conclude that both murrelet species have declined since 1972, with the lower population size and restricted distribution of the Kittlitz’s Murrelet putting it at greater risk of extirpation in PWS . Kittlitz’s Murrelet may have stabilized after the mid-2000s, but our sample size was insufficient to make a determination . Our results emphasize that future conservation efforts will depend on frequent, long-term monitoring of species-specific trends .