Suchergebnisse

Context Nest predation is a leading cause of nest failure for most ground-nesting birds. Methods that allow for accurate classification of fate and identification of predators are important for understanding productivity and conservation strategies. Past studies have used a visual inspection of nest remains to determine nest fate and predict predator identity. Most formal assessments of these methods have addressed small-bodied birds nesting in trees or shrubs, and have revealed that use of evidence at nests can be relatively accurate for determining nest fate but may lead to incorrect conclusions regarding predator identity. However, few have tested the latter hypothesis for larger ground-nesting birds with precocial young. Aim We aimed to evaluate a classification system developed for determining nest fate and identifying predators of waterfowl nests, at both the scale of individual nests and across the study area. Methods From 2016 to 2020, we located 989 blue-winged teal (Spatula discors), mallard (Anas platyrhynchos) and gadwall (Mareca strepera) nests in central North Dakota. We placed cameras at a subset of 249 nests and recorded evidence of nest remains at depredated nests. Key results The most common predators were American badgers (Taxidea taxus), followed by striped skunks (Mephitis mephitis), raccoons (Procyon lotor) and red foxes (Vulpes vulpes). Using evidence of nest remains, we determined nest fates with high accuracy (98.0%). However, evidence of nest remains was only sufficient for identifying predators at 50% of nests, and the classification system was correct only 69.7% of the time. The predicted proportion of predators across the study area differed between the classification system and our video evidence as well. Conclusions The accuracy of predator identifications based upon the classification system that we evaluated was not supported at any scale. Implications Our results suggest that evidence of nest remains can be used to determine nest fate for large-bodied precocial, ground-nesting birds, but accurate identification of nest predators will require alternative methods such as nest cameras.

Grizzly bears have been observed with increasing frequency in northern Manitoba, Canada over the last four decades (1980 – 2020), likely originating from the established population in Nunavut and the Northwest Territories. We summarize and present an interdisciplinary synthesis of documented observations of grizzly bears in northern Manitoba from historical records from the Hudson's Bay Company Archives, published literature, direct observations, remote camera observations, government agency reports, the first author's field notes, volunteered observations, and media and social media reports. A total of 160 observations were recorded, 140 of them since 1980. Spatially, these observations all fall within the Southern Arctic, Hudson Plains, and Taiga Shield ecozones within Manitoba and span from the northern limit of Manitoba at the Nunavut border to the south shore of the Nelson River. Grizzly bears were historically present in northern Manitoba prior to 1980, though in very low numbers, but the frequency of observations has increased significantly since then. Most observations (86%) were less than 1 km from the Hudson Bay coast. Grizzly bears appear to select for open habitats and against forested ones. Reported observations, however, have been largely opportunistic, and the geographical distribution of observer efforts was uneven, so our data likely contain spatial and temporal biases. All confirmed observations were of single bears, suggesting that the present population is likely maintained by dispersal from the population to the north. Understanding grizzly bear ecology, distribution, and demographics north and west of Churchill will be critical for more accurately assessing the status and conservation needs of grizzly bears in the province. ; Au cours des quatre dernières décennies (1980 – 2020), de plus en plus de grizzlis ont été observés dans le nord du Manitoba, au Canada, vraisemblablement en provenance de la population établie au Nunavut et dans les Territoires du Nord-Ouest. Nous résumons et présentons une synthèse interdisciplinaire d'observations documentées de grizzlis dans le nord du Manitoba à partir de dossiers historiques des archives de la Compagnie de la Baie d'Hudson, d'ouvrages publiés, d'observations directes, d'observations en provenance de caméras à distance, de rapports d'organismes gouvernementaux, de notes prises sur le terrain par les principaux auteurs, d'observations participatives ainsi que de signalements prélevés dans les médias et les médias sociaux. Dans l'ensemble, 160 observations ont été consignées, dont 140 depuis 1980. Du point de vue géographique, ces observations ont toutes été faites dans les écozones du sud de l'Arctique, des plaines hudsoniennes et de la taïga du Bouclier du Manitoba, allant de la limite nord du Manitoba à la frontière du Nunavut jusqu'à la rive sud du fleuve Nelson. Les grizzlis étaient présents dans le nord du Manitoba avant 1980, bien qu'en très petits nombres, mais la fréquence des observations s'est accrue considérablement depuis cette époque. La plupart des observations (86 %) ont été faites à moins d'un kilomètre de la côte de la baie d'Hudson. Les grizzlis semblent opter pour les habitats ouverts au détriment des habitats forestiers. Cependant, les observations signalées sont largement opportunistes et la répartition géographique des efforts des observateurs n'était pas égale, ce qui signifie que nos données sont vraisemblablement empreintes d'un biais spatial et d'un biais temporel. Toutes les observations confirmées se rapportaient à des ours seuls, ce qui suggère que la présente population découle probablement de la dispersion de la population du Nord. La compréhension de l'écologie, de la répartition et de la démographie des grizzlis au nord et à l'ouest de Churchill jouera un rôle critique dans l'évaluation plus précise de l'état des grizzlis et de leurs besoins en conservation au sein de la province.