Meeting Abstract
Many species experience a seasonal decline in clutch size, and theoretical models predict two possible, non-exclusive pathways influencing this relationship: 1) poor condition at arrival on the breeding grounds may delay laying and thereby reduce investment in the clutch, or 2) later arriving females may have reduced resource availability to support the formation of a large clutch. If lower condition or later-arriving females can gain in condition at a faster rate they may be able to lay larger than expected, earlier clutches. Lipid accumulation and management is critical prior to laying in common eiders (Somateria mollissima) which must accumulate significant fat stores prior to laying to both fuel follicle growth and deposit the fat stores needed to successfully complete their 24-day incubation fast. Here we use an 11-year data set collected from East Bay Island, NU, Canada, in pre-recruiting, Arctic-nesting female eiders to examine the effect that fattening rate may have on clutch size. We quantify fattening rate using plasma triglycerides (TRIG) and energetic metabolite. Path analyses revealed that fattening rate had an indirect effect on clutch size via a direct influence on the timing of laying: females with higher fattening rates (TRIG) laid earlier and produced larger clutch sizes. Our results are the first to provide mechanisms underlying the well-documented seasonal decline in clutch size across species, namely that fattening prior to breeding indirectly influences reproductive investment via changes to breeding phenology.
