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After 4 weeks of nights showing less than 5 dbz (see reflectivity graphic below) of migration consisting probably mostly of Juncos and Tree Sparrows, temperate migrant intensity picked up the night of March 26-27 initiating a very warm period that lasted until April 5. This period brought the typical first wave of temperates such as Song Sparrow, Sapsucker, Hermit Thrush and Myrtle Warbler. More than one observer noted how quickly Fox Sparrows seemed to pass through southern Wisconsin as we saw night after night of good tailwind weather. Unusual though this year was a blocking weather pattern that set in on April 6 and lasted until May 2 consisting of a stationary low over southern Canada creating a strong fall-like NW flow that kept intensities at <15 dbz until May 3. In 2004 there were 9 nights of migration >15 dbz during April vs. 2 in 2005. This pattern prevented early arrivals of Neotropicals that we often see the last half of April on warm southerly flows such as the earlier arrivals that were recorded in 2004.

The nights on the 17th and the 21st produced small waves of more Myrtles and our first good movement of White-throats, but the bulk of these was delayed until early May. By the last 3 days of April the first Neotropical swarms could be seen nightly building slowly into central and then northern Illinois. It was not until May 3 that the low moved east and a southerly flow was established and we saw a major wave the night of May 3-4. The lack of migration in April suddenly transformed into nightly big waves bringing us many late April migrants as well as the first waves of Neotropicals that built into a first major peak on the night of May 8-9. This is usually the earliest night for this first big wave, usually occurring in southern Wisconsin from the 9th to the 12th. Nightly migration was slowed by cold fronts from the 10th-15th and then the expected single big night occurred on May 16-17 when Milwaukee saw 32 dbz and LaCrosse hit 37 for the State's seasonal high.

On most nights LaCrosse was 10-15% higher in reflectivity values over Milwaukee-Sullivan illustrating the larger number of birds using the Mississippi Valley corridor and its high quality habitat. Green Bay would on most nights be the same intensity as Milwaukee. GB patterns are less likely to be effected by E or NE winds that can easily push birds well inland reducing  intensity. Initial heavy wave nights over SE Wisconsin are reflected in subsequent nights of increased intensity over Green Bay. Generally there would be a 2 night delay after initial big waves seen at LaCrosse to be reflected at Duluth-Superior.

A great deal of new documentary imagery was collected including detections of the major corridor of migration through Door Co. into the UP, fallout patterns at dawn, velocity (migrant flight directions) detections illustrating locations where migrants need shoreline habitat and dozens of others. Lake ascension and crossing were regularly seen but were nearly always from west to east with only one night of a strong crossing from Michigan on a ESE flow.  Beginning about May 25 migration peaked earlier in the late evening after exodus, often beginning a decline after 11 p.m., but still sustained at a lower intensity than peak until dawn. Birds seem to be flying lower in altitude with increased Lake avoidance and greatly reduced crossing perhaps illustrating the lower diversity of species. Note that as the season of record ends that migration is still ongoing nightly and of moderate intensity and will probably be detectible until June 15-17.

 John Idzikowski

  June 1, 2005