39 research outputs found
The Use of Remote Sensing to Evaluate Shorebird Habitats and Populations on Prince Charles Island, Foxe Basin, Canada
No full textLandsat-5 Thematic Mapper imagery was used to produce a 17-habitat classification of Prince Charles Island, Foxe Basin, Northwest Territories, through a combination of supervised and unsupervised approaches. Breeding shorebirds and habitats were surveyed at 35 study plots in July 1989. Habitat-specific breeding densities calculated from these observations were used to estimate total populations of breeding shorebirds on the island based on areas of habitat derived from the classified image. Breeding densities were further modelled in two ways: first, to adjust for distance from the coast, where regression analyses found a significant relationship between distance and density, and second, to include only those pixels of areas considered suitable for breeding, using results of a proximity analysis to determine habitat associations between known breeding locations (pixels) and other habitats. Six species of shorebirds were found breeding on Prince Charles Island, with a combined population (after modelling) estimated at 294 000 pairs. Comparison of breeding densities and estimated populations of shorebirds with those recorded at other arctic locations indicated that Prince Charles Island supports highly significant numbers of shorebirds, especially white-rumped sandpipers and red phalaropes. Comparison of reference areas of known habitat with those on the classified image indicated classification accuracy averaged over 90%. Remote sensing appears to offer a reliable method for assessing habitats and regional breeding populations of birds in at least some areas, providing that classification methods are carried out in a carefully controlled manner. Use of the method over broad areas of the Arctic would require considerable work to recalibrate imagery for different geographic regions.On a utilisé des images de cartographie thématique obtenues avec le Landsat-5 pour répartir en 17 classes les divers habitats de l\u27île du Prince-Charles, située dans le bassin de Foxe (Territoires du Nord-Ouest), et ce, en faisant appel à des méthodes dirigées et non dirigées. En juillet 1989, on a procédé à un relevé des oiseaux de rivage nicheurs et de leur habitat à 35 parcelles-échantillons. On s\u27est servi des densités de nidification spécifiques à l\u27habitat tirées de ces observations pour évaluer la population totale des oiseaux nicheurs de l\u27île, à partir des zones d\u27habitat tirées de l\u27imagerie classifiée. On a procédé de plus à une modélisation des densités de nidification, et ce, à deux fins: d\u27abord, pour tenir compte de la distance depuis la côte, dans les cas où l\u27analyse de régression faisait apparaître un rapport significatif entre distance et densité, ensuite, pour n\u27inclure que les pixels des zones jugées appropriées pour la nidification, en utilisant les résultats d\u27une analyse de proximité visant à déterminer les associations d\u27habitats entre les sites de nidification connus (les pixels) et d\u27autres habitats. On a trouvé que six espèces d\u27oiseaux de rivage nichaient dans l\u27île du Prince-Charles, avec une population globale (après modélisation) évaluée à 294 000 paires. La comparaison des densités de nidification et des populations d\u27oiseaux de rivage estimées avec celles enregistrées à d\u27autres endroits de l\u27Arctique a révélé que l\u27île du Prince-Charles accueille un nombre important d\u27oiseaux de rivage, surtout de bécasseaux à croupion blanc et de phalaropes roux. La comparaison entre les zones de référence d\u27habitat connu et celles de l\u27imagerie classifiée révèle que la précision de la classification atteignait en moyenne 90 p.cent. La télédétection semble offrir une méthode fiable d\u27évaluation des habitats et des populations régionales d\u27oiseaux nicheurs dans au moins certaines zones, à condition que les méthodes de classification soient appliquées avec soin et sous contrôle. L\u27utilisation de la méthode sur de grandes surfaces de l\u27Arctique exigerait un travail considérable de réétalonnage de l\u27imagerie pour différentes régions géographiques
High daily energy expenditure of incubating shorebirds on High Arctic tundra: a circumpolar study
No full text1. Given the allometric scaling of thermoregulatory capacity in birds, and the cold and exposed Arctic environment, it was predicted that Arctic-breeding shorebirds should incur high costs during incubation. Using doubly labelled water (DLW), daily energy expenditure (DEE) during incubation was measured in eight shorebird species weighing between 29 and 142 g at various sites in the Eurasian and Canadian High Arctic. The results are compared with a compilation of similar data for birds at lower latitudes.
2. There was a significant positive correlation between species average DEE and body mass (DEE (kJ day−1) = 28·12 BM (g)^0·524, r^2 = 0·90). The slopes of the allometric regression lines for DEE on body mass of tundra-breeding birds and lower latitude species (a sample mostly of passerines but including several shorebirds) are similar (0·548 vs 0·545). DEE is about 50% higher in birds on the tundra than in temperate breeding areas.
3. Data for radiomarked Red Knots for which the time budgets during DLW measurements were known, indicated that foraging away from the nest on open tundra is almost twice as costly as incubating a four-egg clutch.
4. During the incubation phase in the High Arctic, tundra-breeding shorebirds appear to incur among the highest DEE levels of any time of the year. The rates of energy expenditure measured here are among the highest reported in the literature so far, reaching inferred ceilings of sustainable energy turnover rates.
Imagination and Imaging in Economic Model Building
No full textModelling became one of the primary tools of economic research in the 20th century and economists understand their mathematical models as giving some kind of representation of the economic world, one adequate enough for the purpose of reasoning about that world. But when we look at examples of how non-analogical models were first built in economics, both the process of making representations and aspects of the representing relation remain opaque. Like early astronomers, economists have to imagine how the hidden parts of their world are arranged and to make images, that is, create models, to represent how they work. The case of the Edgeworth Box, a widely used model in 20th century economics, provides a good example to explore the role of imagination and images in the process of making representations of the econom
Staging Studies of Knots Calidris Canutus Islandica in Iceland in the Early 1970s: Body Mass Patterns
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