Covariation among demographic and climate parameters in whiskered auklets Aethia pygmaea

摘要

Annual survival rate and other demographic parameters of whiskered auklets Aethia pygmaea, a small planktivorous seabird, were measured at Buldir Island Alaska during 1992-2003 to provide comparative information for auk life history studies and to test for links among climate, age, productivity and survival. Using two 9 m mistnets, we captured and recaptured 384 adult and 193 sub-adult (one year old, a known-age component of our sample) birds as they arrived at the colony after dark during May and June (1,730 capture events). The best fitting model indicated a lower initial survival rate over the first year following marking (0.708 + 0.036 SE), and subsequent survival (mean 0.835 + 0.029) covarying with the Aleutian Low Pressure climate Index, withhigher auklet survival in years with weak low pressure over the Aleutian Islands. Annual survival rate varied from 0.726+-0.127 in 1998-99 to 0.994 + 0.077 in 1994-95, rates similar to those previously reported for least A. pusilla and crested auklets A.cristatella. A model based only on recaptures of known-age birds indicated a lower local survival estimate over the first year following marking (age one to two years), with no other age-effects on survival. Breeding propensity by age inferred from recaptures of birds with fully-developed brood patches that were originally marked as sub-adults (one year olds) indicated 53% breeding at age two, 94% breeding at age 3, 97% breeding at age 4 and 100% breeding thereafter. The sex ratio of the sampled birdswas significantly male biased (60/40), likely due to differences in behaviour between males and females Curing the incubation stage. Taken together, our data indicate that whiskered auklet survival and productivity covaried with continuous variation in large-scale climatic conditions, the mechanism being either negative effects of stormy North Pacific weather or indirect effects on food supplies.