Stable hydrogen isotope (δD) values in songbird nestlings: effects of diet, temperature, and body size
Bibliographic record
Abstract
Stable hydrogen isotopes (δD) can be a powerful tool for estimating the large-scale movements of animals, but the cause and extent of isotopic variation within animal tissues remain poorly understood. Here, we simultaneously examined three hypotheses to explain δD variation in the blood (δD B ) of nestling Tree Swallows ( Tachycineta bicolor (Vieillot, 1808)) from a single nest-box population in southern Ontario, Canada: (1) microgeographic and (or) temporal variation in δD of local diet, (2) potential evaporation of protium resulting from variation in nest-box temperature, and (3) differences in body size resulting in higher rates of water loss and isotope fractionation in larger birds. δD B ranged from –128‰ to –94‰, with a mean ± SD of –113‰ ± 7‰. Nest-box temperatures ranged from 21.5 to 38 °C immediately prior to blood collection. A general linear mixed-effects model explained 80% of the variation in δD B and provided evidence that δD values in prey, maximum temperature 1 day prior to blood collection, and body size were all significant predictors of δD B . Our results suggest that isotopic variation in individuals and local populations arises from a combination of physiological factors and local environmental variation. To gain a complete understanding of how δD values can be used to estimate animal movements, additional work is needed to determine how these factors influence other tissues, such as metabolically inert feathers, and animals of different age classes.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".