[cobirds] Hypothesis for the Frisco Colorado Purple Sandpiper

COBirders,

 

This is a hypothesis. Frisco, Colorado, is located at N 39.57859/W -106.091118.  Island Beach State Park, New Jersey, at N 39.54189 is an East Coast location where Purple Sandpiper is regular in winter at similar latitude (eBird).  I used Google to tell me a location midway between Frisco and Island Beach State Park. If you continue reading you will see why I did this. Google presented me with Highland, Illinois, at the same approximate latitude and with a longitude of W -89.679264. Following W -89.679264 north into arctic Canada we arrive at the western side of Ellesmere Island, one of the Queen Elizabeth Islands where Purple Sandpipers breed (eBird).  We know small shorebirds can travel about 4000 - 7000 km without stopping to refuel or about 2485 to 4349 miles (Rare Birds of North America by Howell, Lewington, and Russell).  From Ellesmere Island to Frisco, CO, it is about 2970 miles (Google) or well within the range of a flight by a small shorebird before needing to restore its fat reserves and get rid of lipid oxidation. The >100 birders who approached the CO Purple Sandpiper closer than the parking lot or highway should have been able to see the white-edged tertials and wing coverts of a first winter bird (nice photo of a first winter PUSA almost identical in appearance to the CO bird can be viewed in The Crossley I.D. Guide Eastern Birds.)

 

Migrant young birds travel with a built-in compass and clock, while adults who have successfully undergone at least one migration are thought to have a bicoordinate migration system and are thought to sense at least two global coordinates and can, perhaps, unlike young birds, determine their global position and therefore make flight corrections when needed (Rare Birds of North American). Young birds sometimes choose “misorientation” (not disorientation) when their internal compass tells them the directional heading and their internal clock tells them how long to stay in the air (Rare Birds of North American). If either the internal compass or the clock is faulty, perhaps in the case of our Purple Sandpiper its internal compass may have caused our bird to head in the “wrong” direction. One of the well-known types of misorientation is ‘reverse migration’ sending a bird in the mirror image or opposite direction from the direction it would normally fly.  (Fork-tailed Flycatchers migrating north to the U.S. instead of farther south in South America is a good example). Perhaps the 1^st winter Colorado Purple Sandpiper and one from each of these states, Kansas, Oklahoma, Utah, Montana, and Alberta (photos on eBird show me they are all likely 1^st winter birds too) all perhaps had faulty internal compasses sending them in the “wrong” direction. If Iron Spring Creek remains ice free throughout winter months and the seemingly abundant aquatic food supply stays easily accessible, perhaps the Purple Sandpiper could winter at the same latitude Purple Sandpipers frequently choose for spending a winter, but in this case Frisco, Colorado.

 

Bill Maynard

Colorado Springs