Carotenoid skin ornaments as flexible indicators of male foraging behavior in a marine predator: Variation among Mexican colonies of Brown Booby (Sula leucogaster)

Carotenoid-dependent ornaments can reflect animals’ diet and foraging
behaviors. However, this association should be spatially flexible and
variable among populations to account for geographic variation in optimal
foraging behaviors. We tested this hypothesis using populations of a
marine predator (the brown booby, Sula leucogaster) that forage across a
gradient in ocean depth in and near the Gulf of California. Specifically,
we quantified green chroma for two skin traits (foot and gular color) and
their relationship to foraging location and diet of males, as measured via
GPS tracking and stable carbon isotope analysis of blood plasma. Our three
focal colonies varied in which foraging attributes were linked to
carotenoid-rich ornaments. For gular skin, our data showed a shift from a
benthic prey-green skin association in the shallow waters in the north to
a pelagic prey-green skin association in the deepest waters to the south.
Mean foraging trip duration and distance of the foraging site from the
coast also predicted skin coloration in some colonies. Finally, brown
booby colonies varied in which trait (foot vs. gular skin color) was
associated with foraging metrics. Overall, our results indicate that male
ornaments reflect the quality of diet and foraging – information that may
help females select mates who are adapted to local foraging conditions and
therefore, are likely to provide better parental care. More broadly, our
results stress that diet-dependent ornaments are intimately linked to
animals’ environments and that we cannot assume ornaments or ornament
signal content are ubiquitous within species, even when ornaments appear
similar among populations.