. The Canadian field-naturalist. Natural history. 2003 Rodway, Regehr and Chardine: Atlantic Puffins 71 one major colony. We compare our results to previ- ous studies, and extrapolate conclusions about the status of the Great Island breeding population to the Witless Bay population as a whole. Methods Great Island (47° 11' N, 52° 46' W) is part of the Witless Bay Seabird Ecological Reserve and lies approximately km offshore of southeast insular Newfoundland (Figure 1). The island has been described in detail by Nettleship (1972). Three component measurements were used in the calculation of
. The Canadian field-naturalist. Natural history. 2003 Rodway, Regehr and Chardine: Atlantic Puffins 71 one major colony. We compare our results to previ- ous studies, and extrapolate conclusions about the status of the Great Island breeding population to the Witless Bay population as a whole. Methods Great Island (47° 11' N, 52° 46' W) is part of the Witless Bay Seabird Ecological Reserve and lies approximately km offshore of southeast insular Newfoundland (Figure 1). The island has been described in detail by Nettleship (1972). Three component measurements were used in the calculation of a breeding population estimate for puffins on Great Island: burrow density, the propor- tion of burrows that were occupied by nesting birds (occupancy rate), and colony area (Nettleship 1976; Evans 1980; Bibby et al. 1992). Burrow occupancy was determined on 17-28 June 1993 as part of a larg- er study on puffins in 1992-1993 (Rodway et al. 1998). Burrow density was determined and colony area mapped 22 July to 8 August 1994 (more details are given in Rodway et al. 1996*). Burrow density was estimated by calculating the average density of burrows in 237 sample quadrats. Quadrats were distributed using a stratified, centred start, systematic sampling scheme (Madow 1953) to ensure adequate representation of different parts of the colony. Ten permanently marked parallel tran- sects, 100 m apart, were run east and west across the island from a centre line measured down the long axis of the island (Figure 2). Quadrats 2X2 metres in size were established at 5 m intervals throughout the puffin colony along each transect. Numbers of burrows were counted and angle of slope was mea- sured to the nearest degree in each quadrat. An entrance was called a burrow if its tunnel extended more than 50 cm and did not connect with another entrance within 100 cm. In rare cases, tunnels less than 50 cm were called burrows if they contained obvious nest cups, eggs, or chicks. Occupancy rate was dete
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