| Understanding the interactions between different periods of the annual cycle in birds has been constrained by our inability to track individuals outside of the breeding season. I examined whether non-breeding diet quality, prior to arrival on the breeding grounds, influenced reproduction and ornament size in two Pacific seabird species. Diet quality was estimated from stable-carbon and nitrogen isotope signatures in feathers. Cassin's auklet females ( Ptychoramphus aleuticus) that fed on energetically superior copepods (Neocalanus spp.) in the pre-breeding period bred earlier in the season and laid larger eggs than did females that fed on rockfish ( Sebastes spp.). Pre-breeding diet quality was not related to body condition, which suggests that females may need to attain a threshold condition before they initiate breeding. In Rhinoceros auklets (Cerorhinca monocerata ), females that fed on more inshore fish tended to have larger ornaments than females that fed on more euphausiids. Body size was a stronger predictor of ornament size in males than females, suggesting that ornaments may serve as different signals in males and females. This work emphasizes the importance of determining how events are linked throughout the annual cycle for understanding individual success and population abundance. |
