Common Loon migration on Lake St. Clair

From 1995-1997, the Rouge River Bird Observatory took over the coordination of an informal spring Common Loon migration survey that was started at Metro Beach Metropark in Macomb Co. in 1992. Metro Beach lies along the western shore of Lake St. Clair beween Lakes Huron and Erie. RRBO standardized the count methods to try and better understand the migration of Common Loons in the lower Great Lakes.

Over the 6 years, 4114 loons have been counted.

Common Loon migration at Metro Beach, 1992-97

Year Count days Total hours Loons per 10 hrs. Total loons
1992 42 120.0 59.1 709
1993 40 100.5 47.7 479
1994 49 165.0 60.1 991
1995 56 268.0 21.8 583
1996 60 228.0 27.9 637
1997 31 121.5 58.8 715

Flight direction
Of the 2,952 loons whose flight directions were recorded over the six-year period, 47% were traveling north, 37% northwest, and 12% northeast. Only 3% of the loons were flying in a direction with no northerly component. Thus, the Common Loons observed at Metro Beach are clearly migrating.

Dates of passage
Peak flight between 27 April and 2 May: 47.9% of all loons are counted between these days. Most days during the 25 March to 1 June field season are dull, with 70% of the days having fewer than 10 loons.

Wind and weather conditions
Loons have an apparent strong preference for flying into head winds. Out of the 65 days over the five-year period that had 15 or more loons counted, 64.6% of the days had winds with a northerly component. On those days, 83% of the loons were counted on days when winds were blowing from the north (29.7%), northeast (36.1%), or northwest (17.2%). Weather conditions were recorded daily beginning in 1995. During the peak migration period from 27 April to 2 May during 1995-97, only 25% of the days had northerly winds, yet 92.2% of the loons flew on those days. Thus, even though nearly half of all loons will migrate during this 6-day window, the vast majority of them will only fly into a head wind.

Time of passage
Prior to 1995, it appeared that the majority of the loons passed by between 0800 and 1000 EST. This was due primarily to lack of observation time: from 1992-94, 17.75 hours were logged between 0600 and 0800 hours, and about 9.5% of the loons were counted during this time. In 1995-96, 250.75 hours were logged in these two hours, and over 65% of the loons were seen in this time period, a dramatic change. This may indicate that the early loons are birds spending the night on Lake St. Clair (later loons may be birds that spent the night on Lake Erie).

Percentage of loons passing per hour

Time (EST) 1992-94 1995-97 Total
0600-0700 1.5% 45.9% 29.1%
0700-0800 7.9% 22.0% 13.7%
0800-0900 33.5% 13.4% 19.5%
0900-1000 31.0% 5.4% 18.5%
1000-1100 10.8% 8.0% 8.5%
1100-1200 9.9% 5.3% 7.7%
1200-1300 5.3% 0 3.1%

Please note:  All data is provisional and not to be cited without permission.

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