Use of alternate upland nesting habitat reduces brood parasitism in an endangered bird
Bibliographic record
Abstract
The Least Bell’s Vireo (Vireo bellii pusillus) is a federally endangered songbird restricted to Southern California, USA, and Baja California, Mexico. Historically abundant, it suffered a catastrophic population decline during the twentieth century due to widespread habitat destruction and the arrival of Brown-headed Cowbirds (Molothrus ater) within its breeding range. We monitored Least Bell’s Vireo nests and conducted cowbird removals for over 13 years in a protected natural area along the Otay River in San Diego County, California. We evaluated the effects of lay date (day of the first egg laid in each nest), nest habitat (river channel versus adjacent upland terrace), and cowbird removals on Least Bell’s Vireo brood parasitism rates and nest success. Least Bell’s Vireos nested in 11 different host plant species, but over half of vireo nests were found in the upland shrub laurel sumac (Malosma laurina). We located and monitored 177 Least Bell’s Vireo nests, of which 20% were parasitized. The rate of parasitized nests was strongly associated with whether cowbird removals had occurred that season (9%) or had not (35%), despite the low number of female cowbirds removed annually (1–4 females per year). We also found that nests located in the upland terrace had a lower parasitism rate compared to the river channel (12% vs. 29%), with this difference more pronounced in years without cowbird removals. These differences in parasitism rates also drove differences in nest success; only 29% of channel nests were successful versus 48% of nests on the terrace. The best model predicting cowbird brood parasitism included lay date, cowbird removals, and nest habitat (river channel versus upland terrace). Thus, recovering populations of Least Bell’s Vireos may benefit by nesting outside of riparian habitats in adjacent upland habitat due to reduced cowbird parasitism rates. Conservation and restoration of upland habitats adjacent to riparian areas may provide refugia from cowbird parasitism, allowing for continued population increases in areas with limited funding for cowbird management. Conservation of upland habitats will also increase habitat available to Least Bell’s Vireos under future drier climate scenarios.
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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".