The numerical response of great horned owls to the snowshoe hare cycle in the boreal forest
Notice bibliographique
Résumé
Great homed owls (Bubo virginianus) are among the most opportunistic avian predators. In the subarctic boreal forest, their diet consists mainly of snowshoe hares (Lepus americanus), which show extreme population cycles with a 8-11 year period. The aim of this thesis was to study the population ecology of great homed owls in a cyclic environment, to investigate the components of the numerical response of this predator to its prey, and to evaluate the evolutionary context of the ecological processes involved. The study was conducted from 1989-92, with some data from 1988 and 1993, at Kluane Lake in the southwestern Yukon, Canada. During the increase phase of the snowshoe hare cycle, 86% of resident owl pairs bred and raised large broods of 2.4-2.6 fledglings per successful nest. Survival of young owls in their first two years of life was high, and two females were observed to breed as yearlings. Densities of territorial owls almost doubled to a maximum of 21-24 pairs/100km² from 1988-92, but most owls that recruited locally became non-territorial 'floaters', presumably because social behaviour limited the number of territories. Floaters were silent, their ranges overlapped with those of territorial birds, and their density reached 40-50% of the total population. Snowshoe hares began to decline in the winter of 1990/91, and the number of great homed owls recruited in fall dropped from 1.7/pair in 1989-90 to 0.3/pair in 1991. Proximate causes of high pre-dispersal mortality included predation by mammals and parasitism by black flies (Simuliidae) and by Leucocytozoon ziemanni, a blood parasite transmitted by these flies. Post-dispersal mortality and emigration of resident owls also increased as hare densities declined further, floaters being affected before territorial birds. Owl densities continued to increase after the hare peak and then declined with a time lag of one year for floaters, and two years for territory holders. Responses to brood size manipulations and food additions suggested that food was not super-abundant during the prey peak. I conclude that territorial behaviour is essential in causing time lags, with some birds monopolizing resources and conserving energy by ceasing reproduction. A review of life history variation in northern owls showed that great horned owls are constrained in their phenotypic plasticity to increase reproduction at high prey levels compared to some other species. Based on a comparison of evolution in the genera Bubo and Nyctea, I hypothesize that habitat-specific differences in the availability of prey during reproduction, and also in the mortality on age classes during bottlenecks, favoured the diversity of life histories in northern owls.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».