. The Canadian field-naturalist. Natural history. Habitat types ? Rock H Grass tussock 52 Grass-Rubus ESI Forest I Exposed peat 100 200 Metres Figure 3. Distribution of vegetation types on Great Island, Newfoundland, in 1994. occupancy rate of ± breeding pairs/burrow, yields a breeding population estimate of 123 066 ± 7029 pairs. Rounding off, we estimate the current breeding population of Atlantic Puffins on Great Island to be 116 000 - 130 000 pairs. Discussion Comparison of the present vegetation distribution (Figure 3) with that in 1968-1969 (Figure 2 in Nettleship 1972) indicate
. The Canadian field-naturalist. Natural history. Habitat types ? Rock H Grass tussock 52 Grass-Rubus ESI Forest I Exposed peat 100 200 Metres Figure 3. Distribution of vegetation types on Great Island, Newfoundland, in 1994. occupancy rate of ± breeding pairs/burrow, yields a breeding population estimate of 123 066 ± 7029 pairs. Rounding off, we estimate the current breeding population of Atlantic Puffins on Great Island to be 116 000 - 130 000 pairs. Discussion Comparison of the present vegetation distribution (Figure 3) with that in 1968-1969 (Figure 2 in Nettleship 1972) indicated that forested area has contracted and perimeter grassy and meadow habi- tats have expanded. Long-term residents that have fished around Great Island throughout this century report similar observations (J. Reddick, personal communication). Changes are especially obvious on the southern end, which is now virtually devoid of forest, and along the eastern and northern sides of the island. The activities of nesting birds, particular- ly puffins and Herring Gulls (Larus argentatus), likely contributed to habitat changes. Our estimate of 123 000 pairs of Atlantic Puffins nesting on Great Island in 1993-1994 probably underestimates the actual number nesting due to two sources of bias inherent in our methodology. First, the area of the colony was likely underestimated because of the complex, fractal nature of natural habitats (Pennyeuiek and Kline 1986). We corrected our colony area estimate to account for differing slopes in quadrats spaced 5 m apart along transects. which were spaced 100 m apart. However, smaller hills or valleys between quadrats or transects would not have been characterized at our scale of measure- ment. Second, occupancy rates may have been underestimated because any burrow in which an egg had been lost and not replaced before the single check during incubation would not be considered occupied. Although the present estimate is conserva- tive, results from futur
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