Determining Seabird Body Condition Using Nonlethal Measures

Abstract

Energy stores are critical for successful breeding, and longitudinal studies require nonlethal methods to measure energy stores ("body condition"). Nonlethal techniques for measuring energy reserves are seldom verified independently. We compare body mass, size-corrected mass (SCM), plasma lipids, and isotopic dilution with extracted total body lipid content in three seabird species (thick-billed murres Uria lomvia, all four measures; northern fulmars Fulmarus glacialis, three measures; and black-legged kittiwakes Rissa tridactyla, two measures). SCM and body mass were better predictors of total body lipids for the species with high percent lipids (fulmars; R2 = 0.5-0.6) than for the species with low percent lipids (murres and kittiwakes; R2 = 0.2-0.4). The relationship between SCM and percent body lipids, which we argue is often a better measure of condition, was also poor (R2 < 0.2) for species with low lipids. In a literature comparison of 17 bird species, percent lipids was the only predictor of the strength of the relationship between mass and total body lipids; we suggest that SCM be used as an index of energy stores only when lipids exceed 15% of body mass. Across all three species we measured, SCM based on the ordinary least squares regression of mass on the first principal component outperformed other measures. Isotopic dilution was a better predictor of both total body lipids and percent body lipids than were mass, SCM, or plasma lipids in murres. Total body lipids decreased through the breeding season at both sites, while total and neutral plasma lipid concentrations increased at one site but not another, suggesting mobilization of lipid stores for breeding. A literature review showed substantial variation in the reliability of plasma markers, and we recommend isotopic dilution (oxygen-18, plateau) for determination of energy reserves in birds where lipid content is below 15%.

Year-long deployments of small geolocators increase corticosterone levels in murres

“…We used body mass rather than scaled mass index or size-adjusted mass, because scaled mass index does not predict energy stores ('body condition') in seabirds, including murres, and size-adjusted mass does not substantially improve predictability in murres (Jacobs et al 2012). For each parameter (mass and corticosterone), we constructed a general linear model with Sex, Colony and Treatment as covariates.…”

Parents are a Drag: Long-Lived Birds Share the Cost of Increased Foraging Effort with Their Offspring, but Males Pass on More of the Costs than Females

“…Lipid analyses followed established protocols and standards [57], [34]. Briefly, plasma was added to Folch reagent (2∶1 v/v) and filtered [57].…”

“…High levels of circulating neutral lipids are associated with high energy expenditure (chick-rearing murres [26]; small fish [31]; birds [27], [32], [33]. Plasma neutral lipid level is associated with parental mass loss during chick-rearing [34], as lipids are mobilised to fuel increased energy spent flying, and parental mass during chick-rearing is negatively correlated with the mass gain of chicks [35], [36]. Plasma lipids are potentially a better measure of energy mobilisation than body mass because changes in body mass can represent changes in non-lipid portions [37], [26].…”

Applicability of the doubly labelled water method to the rhinoceros auklet, Cerorhinca monocerata

“…A recent study found that body water pool derived 18 O using the plateau method has the highest correlation with actual amount of body water pool (Jacobs et al, 2012). Therefore, in our study, N o and R dilspace determined by the plateau method were used for the calculation of metabolic rates using the one- and two-pool models.…”