Population Change in a Marine Bird Colony is Driven By Changes in Recruitment
Bibliographic record
Abstract
The population dynamics of long-lived birds are thought to be very sensitive to changes in adult survival.However, where natal philopatry is low, recruitment from the larger metapopulation may have the strongest effect on population growth rate even in long-lived species.Here, we illustrate such a situation where changes in a seabird colony size appeared to be the consequence of changes in recruitment.We studied the population dynamics of a declining colony of Ancient Murrelets (Synthliboramphus antiquus) at East Limestone Island, British Columbia.During 1990-2010, Ancient Murrelet chicks were trapped at East Limestone Island while departing to sea, using a standard trapping method carried on throughout the departure period.Adult murrelets were trapped while departing from the colony during 1990-2003.Numbers of chicks trapped declined during 1990-1995, probably because of raccoon predation, increased slightly from 1995-2000 and subsequently declined again.Reproductive success was 30% lower during 2000-2003 than in earlier years, mainly because of an increase in desertions.The proportion of nonbreeders among adult birds trapped at night also declined over the study period.Mortality of adult birds, thought to be mainly prebreeders, from predators more than doubled over the same period.Apparent adult survival of breeders remained constant during 1991-2002 once the first year after banding was excluded, but the apparent survival rates in the first year after banding fell and the survival of birds banded as chicks to age three halved over the same period.A matrix model of population dynamics suggested that even during the early part of the study immigration from other breeding areas must have been substantial, supporting earlier observations that natal philopatry in this species is low.The general colony decline after 2000 probably was related to diminished recruitment, as evidenced by the lower proportion of nonbreeders in the trapped sample.Hence the trend is determined by the recruitment decisions of externally reared birds, rather than demographic factors operating on the local breeding population, an unusual situation for a colonial marine bird.Because of the contraction in the colony it may now be subject to a level of predation pressure from which recovery will be impossible without some form of intervention.RÉSUMÉ.On pense que la dynamique des populations d'oiseaux ayant une longévité accrue est sensible aux changements dans la survie des adultes.Toutefois, lorsque le degré de philopatrie est faible, le recrutement au sein de la métapopulation a peut-être davantage d'effet sur le taux de croissance de la population, même chez les espèces à longévité accrue.Dans le présent article, nous illustrons un cas où les changements d'effectifs d'une colonie d'oiseaux marins semblent être la conséquence des fluctuations du taux de recrutement, au moyen de l'étude de la dynamique de population d'une colonie de Guillemots à cou blanc (Synthliboramphus antiquus) en déclin à l'île Limestone Est en Colombie-Britannique. De 1990 à 2010, de jeunes guillemots ont été capturés sur l'île Limestone Est au moment de quitter la colonie, à l'aide d'une méthode de capture standard utilisée tout au long de la période des départs.Les guillemots adultes ont pour leur part été capturés au moment de leur départ de la colonie, de 1990 à 2003.Le nombre
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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 | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".