. The Canadian field-naturalist. 194 The Canadian Field-Naturalist Vol. 112 The convoluted Lake Superior shoreline probably provides adequate visual isolation between territo- ries, thereby reducing the probability of territorial encounters (Strong and Bissonette 1988). Consequently, it may be that loons are not moving about to establish territories, but instead are pair- bonding and/or searching for nest sites as suggested by Evers (1994). Males spent slightly more time foraging (12% -vs- 7%) and resting (14% -vs- 11%) than females during the pre-nesting stage, perhaps because of their greate
. The Canadian field-naturalist. 194 The Canadian Field-Naturalist Vol. 112 The convoluted Lake Superior shoreline probably provides adequate visual isolation between territo- ries, thereby reducing the probability of territorial encounters (Strong and Bissonette 1988). Consequently, it may be that loons are not moving about to establish territories, but instead are pair- bonding and/or searching for nest sites as suggested by Evers (1994). Males spent slightly more time foraging (12% -vs- 7%) and resting (14% -vs- 11%) than females during the pre-nesting stage, perhaps because of their greater investment in territorial defense (agonistic encounters, 3% -vs- 0; Figure 1). Courtship and copulation between loons is subtle and was observed twice during this study only through chance encounters. As expected, incubation was the most frequent activity during the nesting stage for both males and females (58% and 51%, respectively) (Figure 2). Males incubated during most of the afternoon and evening hours, and females were predominantly on the nest during the morning (Table 1). No definite nest-exchange schedule could be delineated for Lake Superior loons, but male loons on Isle Royale were typically found on the nest in early evening, whereas females tended to be incubat- ing in early morning. This suggested that pairs exchanged positions after sunset, allowing males to patrol the territory. Mclntyre (1988) stated that, though a stereotypical exchange pattern probably does not exist, loon pairs regularly exchange incuba- tion duties. She suggested that males may patrol the territory at night while their mates are incubating, Table 1. Diurnal distribution of incubation rates (in per- cent-time) for Common Loons on the Lake Superior shore- line of Isle Royale NP, 1992-1993. N = 3 territories. Sex Morning Afternoon Evening Male Female 61 124 121 51 130 55 and then exchange places on the nest sometime after sunrise. The advantage to be gained from that type of rotation is the
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