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Front Zool. 2018 Nov 22;15:45. doi: 10.1186/s12983-018-0288-3. eCollection 2018.

Physiological predictors of reproductive performance in the European Starling (Sturnus vulgaris).

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1Department of Biological Sciences, Simon Fraser University, 8888 University Dr, Burnaby, BC V5A 1S6 Canada.
Present address: Springfield College Biology, 263 Alden Street, Springfield, MA 01109-3797 USA.
3Groupe de recherche PRIMUS, Department of Family Medicine, University of Sherbrooke, 3001 12e Ave N, Sherbrooke, QC J1H 5N4 Canada.
Contributed equally



It is widely assumed that variation in fitness components has a physiological basis that might underlie selection on trade-offs, but the mechanisms driving decreased survival and future fecundity remain elusive. Here, we assessed whether physiological variables are related to workload ability or immediate fitness consequences and if they mediate future survival or reproductive success. We used data on 13 physiological variables measured in 93 female European starlings (Sturnus vulgaris) at two breeding stages (incubation, chick-rearing), for first-and second-broods over two years (152 observations).


There was little co-variation among the physiological variables, either in incubating or chick-rearing birds, but some systematic physiological differences between the two stages. Chick-rearing birds had lower hematocrit and plasma creatine kinase but higher hemoglobin, triglyceride and uric acid levels. Only plasma corticosterone was repeatable between incubation and chick-rearing. We assessed relationships between incubation or chick-rearing physiology and measures of workload, current productivity, future fecundity or survival in a univariate manner, and found very few significant relationships. Thus, we next explored the utility of multivariate analysis (principal components analysis, Mahalanobis distance) to account for potentially complex physiological integration, but still found no clear associations.


This implies either that a) birds maintained physiological variables within a homeostatic range that did not affect their performance, b) there are relatively few links between physiology and performance, or, more likely, c) that the complexity of these relationships exceeds our ability to measure it. Variability in ecological context may complicate the relationship between physiology and behavior. We thus urge caution regarding the over-interpretation of isolated significant findings, based on single traits in single years, in the literature.


Dysregulation; European starling; Physiological complexity; Physiological state; Principal components analysis; Reproductive fitness; Statistical distance; Sturnus vulgaris

Conflict of interest statement

All research was conducted under Simon Fraser University Animal Care permits # 657B-96, 829B-96, and 1018B-96.Not applicable.The authors declare that they have no competing interests.Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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