DOI: 10.5061/dryad.905qfttt7
title: Carotenoid skin ornaments as flexible indicators of male foraging behavior in a marine predator: Variation among Mexican colonies of Brown Booby (Sula leucogaster)

description: 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. 
description: We studied three colonies of brown booby from Islas Marietas
 (n=16; July to August 2016), Isla San Pedro Mártir (n=44; January to
 February 2018), and Isla San Jorge (n=17; December 2016 - January 2017)
 Mexico, during the incubation and chick-rearing phases of breeding. To
 measure foraging behavior and habitat use at sea, we tracked brown boobies
 from each colony for 6–10 days using miniature GPS tags. We used tracking
 data to 1) quantify foraging trip duration and total distance traveled on
 unique foraging trips (as indicators of foraging behavior), and 2) measure
 ocean depth and distance to coast at foraging locations (two physical
 variables describing the environment). The mean values of tracking metrics
 per individual were used for the analyses. To evaluate
 skin color, we measured the reflectance of two brown booby skin traits
  (gular and feet) using a handheld spectrophotometer (MINOLTA CM 2600d,
 Osaka, Japan), which collected reflectance spectra at 10 nm intervals from
 360 to 740 nm (details in Supplementary Materials). Three sequential
 measurements of nonoverlapping patches of the skin were taken from each
 patch and the average of these three measurements was automatically
 calculated by the device and was used to obtain the spectra data to
 calculate a green chroma variable (sum of reflectance from 480-550 nm/sum
 of reflectance from 360 to 700 nm) for the gular and the foot
 regions. For a subsample of tracked brown boobies, we
 analyzed the stable carbon isotopic composition of blood plasma, which was
 collected from birds upon retrieval of GPS tracking devices (San Jorge
 n=17, San Pedro Mártir n= 20, Marietas n=14). Stable carbon isotope values
 in brown booby blood plasma likely reflect diet over approximately 10 days
 (Hobson and Clark 1993) and therefore match the period of
 tracking. <strong>Statistical
 Analyses</strong> We used independent linear
 models (LM) to first, assess differences between colonies on foraging
 parameters, diet (estimated by plasma d<sup>13</sup>C), and
 gular and foot color and second, to evaluate the relationship between skin
 color (gular and foot color) and stable isotope data and tracking metrics.
 All variables were standardized within the colony (standardized value = X
 – μ / σ)<strong> </strong>before the analyses to satisfy the
 linearity and homoscedasticity criteria, which were tested using the
 Shapiro-Wilk normality test and the studentized Breusch-Pagan test,
 respectively. To facilitate interpretation, we converted
 d<sup>13</sup>C values to positive numbers (by adding 18.9,
 the absolute value of the lowest d<sup>13</sup>C value) before
 standardization. Because data from San Pedro Mártir included males during
 the incubation and chick-rearing period, gular and foot color were
 standardized according to the breeding stage. All statistical analyses
 were conducted in R version 4.2.1 (R Core Team 2022).
description: # Carotenoid skin ornaments as flexible indicators of male foraging
 behavior in a marine predator: Variation among Mexican colonies of Brown
 Booby (*Sula leucogaster*)
 [https://doi.org/10.5061/dryad.905qfttt7](https://doi.org/10.5061/dryad.905qfttt7) ## Description of the data and file structure | Variable | Definition | | | | | :------------ | :--------------------------------------------- | - | - | - | | id | identity of each bird (colonyyearspbandnumber) | | | | | id-bdd | id within the bdd for this project | | | | | colony | 1=San Jorge; 2=San Pedro; 3=Marietas | | | | | stage | 1=incubation; 2=chick rearing | | | | | duration | average trip duration (hrs) | | | | | depth | average depth during searching trips (m) | | | | | distcost | average distance from the cost (km) | | | | | flightdist | Average distance traveled | | | | | searching | average proportion of searching time | | | | | d13C | Delta 13 Carbon isotope data (%) | | | | | gular | Green chroma from gular color (% reflectance) | | | | | foot | Green chroma from foot color (% reflectance) | | | | | std13 | standardized by colony d13C | | | | | std13positive | standardized by colony d13C \* -1 | | | | | stgular | standardized by colony gular green chroma | | | | | stfoot | standardized by colony foot green chroma | | | |