MEPS 564:187-197 (2017)  -  DOI: https://doi.org/10.3354/meps11988

ABSTRACT: Differences in reproductive output for marine vertebrates are driven by a combination of environmental, physiological, and behavioral cues. Individuals use these cues when balancing the tradeoff between current reproductive investment and future survival, particularly when resources vary on spatial and temporal scales. A common strategy for maximizing fecundity in birds is to produce 2 broods in a single season, a behavior known as double brooding. Cassin’s auklets Ptychoramphus aleuticus are among the relatively few seabirds that use this strategy; however, the proportion of breeding pairs that attempt double brooding is highly variable among years. We investigated the source of this variation using long-term monitoring data from Southeast Farallon Island off central California, USA. Double-brooding rates ranged from 0 to 90% over a 26 yr period, with an overall rate of 32% (95% CI ± 4.16%). Parameter estimates from generalized linear mixed models indicate that older females, earlier breeding initiation dates, stronger upwelling, and an interaction between age and upwelling strength increased the likelihood of double brooding in this population. Using a within-subject centering technique, the effects of age included both a within- and between-individual improvement in the likelihood of double brooding with age. Our findings indicate that females of higher quality and reproductive experience drive double brooding in this population and that these individuals are especially able to adopt a more flexible breeding regime in years characterized by high marine productivity.

KEY WORDS: Age-based demography · California Current · Cassin’s auklet · Reproductive strategy · Seabird · Upwelling · Double brooding · Variable environment