Stable isotopes link diet to avian yolk carotenoid allocation: a comparative study of five auk species (Charadriiformes: Alcidae).

The allocation of important but environmentally limited nutrients, such as carotenoids, often represents a trade-off between homeostasis and reproduction. However, key questions remain about how diet and species traits influence carotenoid allocation. We studied yolk carotenoid profiles and yolk color in relation to trophic level (based on delta(15)N values) in five species of seabirds belonging to the family Alcidae: common murre (Uria aalge), pigeon guillemot (Cepphus columba), Cassin's auklet (Ptychoramphus aleuticus), rhinoceros auklet (Cerorhinca monocerata), and tufted puffin (Fratercula cirrhata). In three species, which ranged from low (tufted puffin) to high (pigeon guillemot) trophic level, yolks had pink to red hues and contained exclusively astaxanthin, while yolks of species from a high trophic level (common murre) and from a generalist forager (rhinoceros auklet) had yellow to orange hues and contained astaxanthin, lutein, and zeaxanthin. The absence of a systematic relationship between trophic level and carotenoid types suggests that these species possess adaptations for the uptake and use of specific carotenoids. In contrast, total yolk carotenoid concentrations were best explained by the combination of species and trophic level: lower-trophic-level feeding was linked to production of carotenoid-rich yolks, both across species and within the one generalist species. We conclude that both behavioral and physiological traits can play strong roles in the acquisition and allocation of critical nutrients from mothers to their offspring.