The naked eye, binoculars and spotting scopes are used to scan the sky for migrants. Spotters are often used to help the official counter locate birds. When a raptor is observed, a series of decisions must be made:
In what direction is the bird heading?
Only birds moving west or southwest over the Detroit River are defined as migrating.
Figure 1. Potential flight paths of migrating raptors from Canada to US depending upon wind conditions.
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(Click to enlarge; opens in new window.)
Figure 2. Panoramic image of Lake Erie Metropark count site with key landmarks. View is approximately 4 miles wide from south (Lake Erie, #27, right) to north (Marsh Creek, #1, left). Image courtesy of J.S. Jourdan.
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What is next?
Once it has been determined that the bird is migrating, it is then identified to species using the standard field identification techniques (shape, color, pattern, wing beat cadence, behavior, etc.). If it is not possible to identify the bird, it is recorded as "unidentified." If possible, age and sex are also noted.
The bird is officially tallied only after it passes west/southwest of the observer. Any bird that does not pass that point is not counted. Each migrant species that is observed is recorded on a tabletop clicker with one button for each of 16 species. At the end of the hour, the species totals are documented and the clicker is cleared.
Counting Broad-winged HawksBroad-wings save energy by riding thermals for lift. At times, hundreds or thousands of birds are using the same thermal. The birds are far too difficult to count while in these "kettles" which can look like a tornado swirling with birds.Conveniently for counters, when the birds reach the top of the thermal, they glide out singly or in smaller numbers (often referred to as "streaming out"). As they stream out, the birds can be counted one at a time on our hand-held clickers.If necessary, they are counted 10 at a time (one click represents 10 birds). If there are too many birds for this, a block count method can be used on the stream (e.g., if 40 birds are in one field of view in the binoculars and 25 fields of view are required to scan a given group, 1,000 birds are tallied).
Counting Bald Eagles and OspreyBefore a Bald Eagle or Osprey is officially tallied, it must demonstrate a migratory pattern as opposed to a behavior indicative of a local bird. Birds are not counted as migrants if they are:1. in view for extended periods of time;2. actively hunting, or flying "the wrong way"Bald eagles and osprey are counted if they are:1. using thermals;2. flying a straight course in the correct direction; or3. at a very high altitudeIdentifying individual birds by sex or age assists with the migrant/transient documentation. This procedure allows for a more conservative bald eagle and osprey survey.
The official count site for the Detroit River Hawk Watch is the Boat Launch at Lake Erie Metropark (LEMP). Prior to the late 1990s, numerous count sites were used from Trenton to Brownstown depending on wind conditions, which would alter where the most migratory raptors were crossing the Detroit River from Canada. Since about 1998, coverage was limited to two sites: LEMP and the headquarters of Pointe Mouillee State Game Area (PMSGA) about 2 miles to the south. PMSGA was often used instead of LEMP, especially on days with northerly winds, which pushed birds south of LEMP. At times, the two sites were used simultaneously with the assumption that birds are not "double-counted“ because of the geography of the two locations. However, there were limitations with this protocol because significant coverage gaps occurred at each site. Because the sole objective of counting birds is to systematically "sample" the migration and consistently collect weather data the counts are now conducted exclusively at LEMP. If sufficient coverage is available, a secondary count at PMSGA may be conducted with data reported apart from the day's official tally.
View the Official Site Protocol.