The November 13-14, 2005 Cave Swallow Incursion into Wisconsin and the 

Western Great Lakes-

  Weather Maps and Speculations

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Summary

 

A cyclonic (counter-clockwise) circulation on the east side of a low pressure system that moved rapidly NE from the southern Great Plains and Texas to the upper Midwest created a strong southerly flow from Nov. 12-14 along its track. Timed with the flow ahead and after the passage of the cold front associated with this low  was the appearance of an estimated 600 Cave Swallows noted along the shores of the western Great Lakes. Could this system's flow have involved birds in the late fall Texas range of the expanding SW race of Cave Swallow, pelodoma (=pallida)? Are these birds moving south at this time? This  fallout on the western Great Lakes is similar to that seen from the E-NE or upper right quadrant of a hurricane.  

 

 

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Cave Swallow Observation, Milwaukee Co. North Point, Nov. 13, 2005, 9:30 a.m.

  As a strong low-pressure system tracked into the western Gr. Lakes on Saturday, Nov. 12,  SW wind warnings were issued for Sunday. Such November lows more often bring NE winds and we expect lake ducks, gulls and Kittiwakes concentrating at the shore of Lake Michigan. Such a “reversed” wind event this late in the fall was intriguing so I was at N Point by 8:00 a.m. and saw no land birds following the shoreline. A return to the same spot at 9:30 initially produced more of the same including no raptor movement. As I walked along the path an apparent Cliff Swallow flew slowly to the south, directly overhead, 40 feet away, fighting the wind’s push out onto the Lake while finding some protection as it was below the height of the bluffs to the west seemingly attempting to hawk non-existent insects. Its rufous-buff rump was readily visible as was the squared tail, dark back with some lightish striping barely visible, dark wings. At first I could not see the head and breast, but as it fought the southward push it banked back to the north and I could easily see the light orangish-buff throat extending up into the auriculars unlike the dark throat and pattern of a Cliff. Initially I felt that I was unable to see the forehead of this bird, but based on subsequent observations of the Nov. 14 Oak Creek birds under similar conditions I probably did see this spot briefly but due to overcast and shadow it appeared uniformly dark; even under these conditions the bright buff forehead patch of a Cliff probably would have been visible. Ten minutes later another Cliff/Cave flew over, but quickly headed south and only its rump and silhouette were noted. The subsequent observation of birds at S. Metro the following day along with the pictures I took and impressions from flight shots of other documentations of Caves convinced me of this bird being a Cave Swallow.

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Cave Swallows,Oak Creek, S Metro Pier, Milwaukee Co., Nov. 14- 

    

Cave Swallow from S Metro, November 20, 2005 by Mike McDowell-

caveswallow.jpg (35386 bytes) Click on thumb to enlarge

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Cave Swallow reference shots-

   

Cliff Swallow reference shots for comparison-

   

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Weather Synopsis

1.  Since early November, the jet stream or the upper level "river of wind" at 30,000 feet, a guiding force for our surface weather systems, had been in an essentially west to east direction for several weeks bringing the upper Midwest mild November  weather as cold Canadian air stays to the north. 

Jet stream map for Nov. 9- 

05110912jet.gif (28334 bytes) Click on thumb to enlarge

2.  Note how the jet begins to dip southward and then swings SW to NE over the upper Midwest in a more typical fashion for late autumn. 

Jet stream map for Nov. 12-

05111212jet.gif (29415 bytes)

3.  Note the low pressure system developing over eastern Colorado with its cold front; also note the southerly flow to the Midwest on the backside of the high over the SE. Remember that the barbs pointing from the weather observation stations point towards the direction that the wind is coming from. Note how the southerly flow forms a virtual "train" for possible vagrants from the SW as the low tracks NE, much like we saw in the fall of 2000.

Surface map from 6 p.m. on Nov. 11-

05111200.gif (52814 bytes)

4.  The low strengthens and moves NE; a southerly flow is already ahead of the low on the backside of the high. 

Surface map from 6 a.m. on Nov. 12-

05111212.gif (55931 bytes)

5.  The low moves rapidly to the NE across northern Wisconsin with the strong cold front sweeping across the State; forecasters are warning of high winds with the passage of the low and the attendant cold front as it strengthens and develops a pressure gradient.

Surface map from 6 p.m. on Saturday, November 12-

05111300.gif (57966 bytes)

6.  The cold front passes through Wisconsin before dawn on Sunday morning, Nov. 13; the winds behind the front are SW and quite strong. Experienced observers take to the western shore of Lake Michigan hoping to find migrants concentrated along the shoreline on the SW winds. Two Cave Swallows are encountered on the Lake Michigan shoreline in Milwaukee by 9:30 a.m. In the afternoon a flock of 15 are found feeding around sewage treatment tanks 10 miles to the south.

Surface map from 6 a.m. on Sunday-

05111312.gif (57626 bytes)

7. The strong SW winds continue all day as the low moves rapidly east.

Surface map for 6 p.m. Sunday evening-

 05111400.gif (55928 bytes)

8.  The winds die down Monday morning, the 14th and eventually shift to the SE on the circulation of the high behind the front; the flock moves west with these winds and disappears. At least 2 states, Wisconsin and Ohio have recorded first of state records for Cave Swallow involving flocks of birds- an essentially unheard of occurrence. 

Surface map for Monday morning, dying SW flow-

05111412.gif (57401 bytes)

Surface wind maps for Nov. 11 through Sunday afternoon, Nov. 13. Beginning with the map for 00Z on the 11th. Note the progression of a southerly flow beginning in the southern Gr. Plains and then building  as the Low strengthens and moves into the Midwest. By Sunday morning the Low is producing a strong southwesterly flow into southeastern Wisconsin pushing swallows to the western shore of Lake Michigan.

Discussion and References

It seems probable that this event reflects a perfect weather scenario coinciding with the migration of Cave Swallows, perhaps aided by the expansion and population increase of this race. We will no doubt find out in future autumns as we anticipate the movement of weather systems.  Lows at this time of year often enter the Midwest farther south bringing strong E and NE winds to the western Great Lakes or they come from a more direct westerly direction not involving a strong, continuous wind flow from out of the range of this species and a SW to NE track.

Contrast the movement of these birds associated with the Nov. 12-14 low track and the more typical track of such lows in recent years at this time of year bringing these birds mostly to the eastern Great Lakes and East Coast. See the pdf file from "North American Birds" reviewing the fall, 2004 season on pages 25-27.

Also see-

McNair, D. B., and W. Post. 2001. Review of the occurrence of vagrant cave swallows in the United States and Canada. Journal of Field Ornithology 72 (4): 485-503.  Read the abstract.

U. of Kansas researchers have found that Cave Swallow expansion into northern Texas and no doubt eventually farther north and east is being facilitated by the use by Cave Swallows of old Barn Swallow nests. Nesting success is the same as if they were building their own new nests.
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John Idzikowski

December 12, 2005