The Use of Remote Sensing to Evaluate Shorebird Habitats and Populations on Prince Charles Island, Foxe Basin, Canada

Landsat-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'île 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'est servi des densités de nidification spécifiques à l'habitat tirées de ces observations pour évaluer la population totale des oiseaux nicheurs de l'île, à partir des zones d'habitat tirées de l'imagerie classifiée. On a procédé de plus à une modélisation des densités de nidification, et ce, à deux fins: d'abord, pour tenir compte de la distance depuis la côte, dans les cas où l'analyse de régression faisait apparaître un rapport significatif entre distance et densité, ensuite, pour n'inclure que les pixels des zones jugées appropriées pour la nidification, en utilisant les résultats d'une analyse de proximité visant à déterminer les associations d'habitats entre les sites de nidification connus (les pixels) et d'autres habitats. On a trouvé que six espèces d'oiseaux de rivage nichaient dans l'île du Prince-Charles, avec une population globale (après modélisation) évaluée à 294 000 paires. La comparaison des densités de nidification et des populations d'oiseaux de rivage estimées avec celles enregistrées à d'autres endroits de l'Arctique a révélé que l'île du Prince-Charles accueille un nombre important d'oiseaux de rivage, surtout de bécasseaux à croupion blanc et de phalaropes roux. La comparaison entre les zones de référence d'habitat connu et celles de l'imagerie classifiée révèle que la précision de la classification atteignait en moyenne 90 p.cent. La télédétection semble offrir une méthode fiable d'évaluation des habitats et des populations régionales d'oiseaux nicheurs dans au moins certaines zones, à condition que les méthodes de classification soient appliquées avec soin et sous contrôle. L'utilisation de la méthode sur de grandes surfaces de l'Arctique exigerait un travail considérable de réétalonnage de l'imagerie pour différentes régions géographiques

Philopatry, site tenacity and mate fidelity in the semipalmated sandpiper.

Philopatry, site tenacity, and mate fidelity were examined in a 5-yr study of a population of male-territorial, monogamous Semipalmated Sandpipers (Calidris pusilla) breeding at La Perouse Bay, near Churchill, Manitoba. There was no sex bias in natal philopatry and no significant difference in adult philopatry, although males tended to return to the breeding area at higher frequencies than females. However, males nested significantly closer to previous nests than did females. Pairs that had reunited did not move as far from their previous nest site as birds that had changed mates, and this effect was more pronounced in females. Birds that had nested successfully the previous year returned at higher rates than those that had been unsuccessful. However, there was no significant difference in distance moved from a previously successful vs. unsuccessful nest. There also was no significant difference in site tenacity when distances one and two years or two and three years apart were compared. However, nest distances increased significantly when three years had elapsed between utilization of sites. Each year approximately 50% of the marked birds in the study area had reunited with their mate of the previous year. If both members of the pair returned, close to 80% remained paired. There was no tendency for birds that had "divorced" to have been less successful nesters in the previous year, compared to pairs that had reunited. Subsequent nesting success was not significantly different between birds that had changed or retained mates. However, in 1 of 4 yr, nests of pairs that had changed mates hatched significantly later than did those of remated pairs. Received 23 April 1984, accepted 4 October 1984

Rigorous Results, Cross-Model Justification, and the Transfer of Empirical Warrant: The Case of Many-Body Models in Physics

This paper argues that a successful philosophical analysis of models and simulations must accommodate an account of mathematically rigorous results. Such rigorous results may be thought of as genuinely model-specific contributions, which can neither be deduced from fundamental theory nor inferred from empirical data. Rigorous results provide new indirect ways of assessing the success of models and simulations and are crucial to understanding the connections between different models. This is most obvious in cases where rigorous results map different models on to one another. Not only does this put constraints on the extent to which performance in specific empirical contexts may be regarded as the main touchstone of success in scientific modelling, it also allows for the transfer of warrant across different models. Mathematically rigorous results can thus come to be seen as not only strengthening the cohesion between scientific strategies of modelling and simulation, but also as offering new ways of indirect confirmation