HOW DO BROWN-HEADED COWBIRDS (MOLOTHRUS ATER) CAUSE NEST FAILURES IN SONG SPARROWS (MELOSPIZA MELODIA)? A REMOVAL EXPERIMENT
Bibliographic record
Abstract
A removal experiment was conducted to measure how much and by what mechanisms brood parasitic Brown-headed Cowbirds (Molothrus ater) cause nest failures in a commonly used host, the Song Sparrow (Melospiza melodia). When numbers of female cowbirds were reduced experimentally, nest failures fell from 65.0% (n = 663 nests) to 49.9% (n = 331). Cowbird reduction reduced the frequency of nest failure to one-third of control levels in Song Sparrows during the last 80 days of the sparrow's breeding season, the period when most parasitic laying took place. Cowbird reduction decreased nest failures strongly at the egg stage, and weakly at the nestling stage. Daily nest-failure rates were independent of whether or not a nest was parasitized by cowbirds. Two hypotheses were tested to explain how cowbirds cause host nests to fail: first, egg removal by female cowbirds lowers clutch size below a threshold where the host deserts; second, cowbirds cause host nests to fail by destroying entire clutches or broods. In support of the first hypothesis, desertion following parasitism and egg removal was less frequent when cowbird numbers were reduced (8.9% of n = 158 nests) than for unmanipulated controls (16.5% of n = 424 nests). In support of the second hypothesis, there were fewer cases where young were killed in the nest, or found dead near it, after cowbird numbers were reduced (2.5% of 158 nests) than in controls (4.7% of 424 control nests). In contrast, proportions of nests that failed after the disappearance of all eggs, young, or both, and after unparasitized clutches were deserted, increased when cowbird numbers were reduced. Although our study supports both hypotheses, cowbird-induced desertion had a greater effect on nest failure rates than did cowbird predation. Our study suggests that cowbird removal programs are likely to benefit commonly used and endangered hosts by reducing rates of nest failure.
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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) | 0.001 | 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".