. The Canadian field-naturalist. Natural history; Sciences naturelles. 2005 Lumsden: Grouse Hybridization on Manitoulin Island 511. figure 2. Approximate speed of advance of Sharp-tailed Grouse in northern Michigan and Manitoulin Island, Ontario. Observations on Leks Starting in 1951, watching from a blind on selected leks on Manitoulin Island, I made judgements on wheth- er each male was a hybrid, a Prairie Chicken, undeter- mined or a Sharp-tailed Grouse. I used their plumage markings, aberrations in their displays and the colour of their booming sacks and toes. By 1951, Prairie Sharp- taile
. The Canadian field-naturalist. Natural history; Sciences naturelles. 2005 Lumsden: Grouse Hybridization on Manitoulin Island 511. figure 2. Approximate speed of advance of Sharp-tailed Grouse in northern Michigan and Manitoulin Island, Ontario. Observations on Leks Starting in 1951, watching from a blind on selected leks on Manitoulin Island, I made judgements on wheth- er each male was a hybrid, a Prairie Chicken, undeter- mined or a Sharp-tailed Grouse. I used their plumage markings, aberrations in their displays and the colour of their booming sacks and toes. By 1951, Prairie Sharp- tailed Grouse had only reached the extreme western end of Manitoulin Island and none had appeared on the four leks intensively studied. Counts of these leks (Table 2) suggested that of 48 males present, 28 (58%) were hybrids, 16 (33%) were Prairie Chickens, 4 (8%) were undetermined, and none were Sharp-tailed Grouse. Those in the undetermined category had the appear- ance of Prairie Chickens but slight shortening of the pinnae, or occasional peculiarities of behaviour caused me to question their identity. By 1962, Prairie Sharp-tailed Grouse had taken over at Gore Bay Airport. There were only 3 (23%) hybrids, no Prairie Chickens, but 10 (7%) apparently pure Prai- rie Sharp-tailed Grouse. In 1961, on the extreme eastern end of the Island at the Sheguiandah lek, there were still 10 (83%) hybrids, 2 (17%) Prairie Chickens, and no Sharp-tailed Grouse. Much the same ratios prevailed at Sheguiandah in 1962 when 6 (85%) were hybrids and there was only 1 (15%) Prairie Chicken. However in 1964, Prairie Sharp-tailed Grouse had appeared at Sheguiandah and in 1966 at Ten Mile Point. The proportions of hybrids in each year for each lek studied ranged from 23% to 85% (Table 2). Discussion The hybrid frequency on Manitoulin Island amounts to more than 50% of the population (Lumsden in preparation) but in northern Michigan far less than 1%. There are thus significantly different rates of hybridi- z
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