Assimilation and deposition of wax esters in planktivorous seabirds

We have analyzed the lipid composition of meals fed to chicks and determined the ability of chicks to assimilate wax esters in four species of high latitude, plankton‐feeding seabirds: one alcid ( Aethia pusilla ; Alcidae: Charadriiformes) and three petrels ( Pelecanoides urinatrix, P. georgicus , and Pachyptila desolata ; Procellariiformes). Up to 63% of the estimated digestible energy in chick meals consists of wax esters. Using 14 C‐labeled cetyl palmitate, we have shown that chicks of the four study species efficiently hydrolyze wax esters, with less than 1% of the ingested label excreted in most cases. Labeled fatty acids were assimilated and deposited primarily as triacylglycerols in storage fat depots. The one study species known to store lipids in the proventriculus retained much of the labeled wax ester unhydrolyzed in stomach oils. However, the capacity to store stomach oils was not a requisite for efficient assimilation of wax esters. This study provides the first direct evidence that seabirds have the inherent ability to digest and assimilate wax esters efficiently.