Okay, I will take that bait Ted!
So, according to eBird, I have the earliest two records of Swainson's Hawk in Colorado (yes ALL of Colorado). The first one (previous early arrival record) was on March 2, 2003 in Larimer county (in fact, it was near the border of Weld and Larimer counties somewhere on a frontage road near I-25, I just didn't note the exact location). The new early record arrival for Swainson's Hawk is my Feb 25, 2012 observation (again, according to eBird since the party in Prowers county over the weekend didn't enter data [yet?]). I don't have a copy of "Bob & Bob" to check their data. This somewhat corroborates with Ted's information from eBird. Also interesting from eBird is an animation of Swainson's Hawk occurrence in the United States over a year (Thanks Scott!): http://ebird.org/results/STEM/animations/SWHA_large.gif Interesting in this animation is the early returns to the California Central Valley in late February or early March. Are these birds from a different population/subspecies or are they just taking advantage of some weather phenomenon that occurs along the West Coast/Central Valley at this time of year, or is it something else completely? That is my kind of question, but I don't have any data to support or disprove the notions. At the time of my sighting, the winds were howling out of the west and southwest at the surface varying slightly with each gust. The winds from the middle of the atmosphere down to the surface were nearly the same. Here are the maps to "prove" it: Surface streamlines -> http://www.atmos.illinois.edu/~bguaren2/birdweather/archive/2012022500_nam_stream_sfc_06.gif .75 km above sea-level streamlines (note the above sea-level, so the winds in the mountains should be discounted) -> http://www.atmos.illinois.edu/~bguaren2/birdweather/archive/2012022500_nam_stream_900_06.gif 1.5 km above sea-level streamlines (note the above sea-level, so the winds in the mountains should be discounted) -> http://www.atmos.illinois.edu/~bguaren2/birdweather/archive/2012022500_nam_stream_850_06.gif 2.5 km above sea-level streamlines -> http://www.atmos.illinois.edu/~bguaren2/birdweather/archive/2012022500_nam_stream_700_06.gif 5.0 km above sea-level streamlines -> http://www.atmos.illinois.edu/~bguaren2/birdweather/archive/2012022500_nam_stream_500_06.gif I can't say I would have expected strong migration on this day. The only thing I see that "might" be interesting is the wind pattern from Baja up to Colorado at multiple levels (.75km, 1.5km, 2.5km, and to a lesser degree 5.0km above sea level). This might be an indication that these birds were from that area, but there is no current way to tell. GPS tracking sounds like a great idea to me, but the success rate of bird-borne GPS is so low until recently, that it doesn't really bode well for a meteorology x ornithology study. Today is a great example of what I think could lead to a LOT of hawk migration. http://www.atmos.illinois.edu/~bguaren2/birdweather/archive/2012022700_nam_stream_850_12.gif Winds all along the Yucatan peninsula wrap south around the Gulf of Mexico then north along that very common flyway for hawks (the east coast of Mexico through Veracruz), then north into the central plains and specifically along the eastern slope of the Rocky Mountains. The surface heating is likely leading to convection (with or without clouds) which seems ideal for raptor migration. Without a lot of further analysis, this is as far as I can get. Bryan Guarente Instructional Designer/Meteorologist The COMET Program University Corporation for Atmospheric Research Boulder, CO -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/cobirds?hl=en.
