Bill's hypothesis lines up exactly with what I was thinking regarding how this bird got to CO, but I wanted to take the speculation a bit further. Here's an additional thought on how it might have gotten it's directions wrong.
First, simple mutation or developmental issues might muck up such a system, or perhaps it hooked up with some other species and followed the wrong flock. But here's another option (admittedly a very remote one): it's not a pure North American bird. Purple Sandpiper is a holarctic species, and breeds along the northern edge of Europe and the western parts of the Asian arctic. Those Eurasian birds migrate WEST, not EAST like the North American birds. There is evidence from other bird (songbird) spec that the direction of that "internal compass" is heritable, and typically a youngster will tend to migrate in roughly the same direction as it's parents. So if mom and dad happen to have genes telling them to migrate two different directions, studies in songbirds suggest that this might cause youngsters to want to travel in a direction that is somewhere in the middle. So, while I suspect this is a "pure" North American bird with a bad compass (as suggested by the migratory patterns of the species and patterns of vagrancy mentioned by Bill), the thought had also crossed my mind that perhaps this is a bird with a mix of American and European Purple Sandpiper genes (seems unlikely, I know!) who split the difference of heading SW and SE and just went South. As far fetched as it sounds, this is one of those fun little mysteries we'll probably never know the answer to. Then again, should this bird perish and some or all of it's remains are found, the answer might be there in it's DNA, and so those remains should immediately be put on ice and taken to CU Boulder (or perhaps the Denver Museum of Nature and Science) where we might be able to preserve those tissues for later genetic work. Just a thought :-) Good birding, Paul Hurtado PS: Thank you all for the continued updates!! There are still a few of us who haven't had a chance to chase this bird. I hope to make a trip up to Frisco later this week, so with a little luck it'll stick around for me! ;-) On Mon, Dec 26, 2016 at 8:14 AM, Bill Maynard <[email protected]> wrote: > 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 1st 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 1st 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 > > > > > > -- > You received this message because you are subscribed to the Google Groups > "Colorado Birds" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > To view this discussion on the web visit https://groups.google.com/d/ > msgid/cobirds/000301d25f93%242adacfa0%2480906ee0%24%40com > <https://groups.google.com/d/msgid/cobirds/000301d25f93%242adacfa0%2480906ee0%24%40com?utm_medium=email&utm_source=footer> > . > For more options, visit https://groups.google.com/d/optout. > -- Paul J. Hurtado Assistant Professor of Mathematics & Statistics Ecology, Evolution and Conservation Biology University of Nevada, Reno http://www.pauljhurtado.com/ -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/cobirds/CABpQ-FUKxp2NOapTVWa-yh%2BbyxjmeH6rU4H4ccAH2_4SyufNbQ%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
