. The Canadian field-naturalist. The Canadian Field-Naturalist Vol. 86 Table 1. — - Starting times (within hours oi sunrise). 1 Hour 1-2 Hrs. 2+ Hrs. Total days April May 20% 70% 45% 35% 20 30 Table 2. — Number of days as a function of observing hours during April and May Less than 3 hours April May 1* 4* 6 3* 5 3 2 9 2 7 8 *Weather factor. synoptic weather maps of eastern North Amer- ica and associated data at six-hourly intervals throughout the study period. Weather condi- tions, wind speed and direction at the Main Duck Islan
. The Canadian field-naturalist. The Canadian Field-Naturalist Vol. 86 Table 1. — - Starting times (within hours oi sunrise). 1 Hour 1-2 Hrs. 2+ Hrs. Total days April May 20% 70% 45% 35% 20 30 Table 2. — Number of days as a function of observing hours during April and May Less than 3 hours April May 1* 4* 6 3* 5 3 2 9 2 7 8 *Weather factor. synoptic weather maps of eastern North Amer- ica and associated data at six-hourly intervals throughout the study period. Weather condi- tions, wind speed and direction at the Main Duck Island, five miles east of were also provided by them at six-hourly intervals. No major kills occurred at the hghthouses on Main Duck I. nor False Ducks I. in the study period. PART I. PATTERNS OF MIGRATION Results and Discussion Abundance of Migrants The eastern end of Lake Ontario lies between the Atlantic Flyway and the Mississippi Fly- way. Birds from both flyways are found here but obviously their density will be much less than closer to either flyway. Diurnal observa- tions will probably not give a true picture of the total volume of migration. Many nocturnal migrants will pass directly over. It has been found that the number of grounded migrants represents a variable proportion of the number flying overhead (Lack, 1960). It is impossible to determine the total number of birds in our relatively large survey area. However, because of the systematic method of the study, daily differences should have meaning and broad trends in population levels which appear should give a picture of migration in and out. The dif- ferences introduced by inclement observing weather were more easily dealt with than were differences due to observers. There are cases where it is impossible to know whether differ- ences in numbers are statistically significant. Two hundred species including waterfowl were recorded during the study period. Waterfowl. The main migration of several of the divi
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