Tuesday, September 1, 2015

Post #35 - Fall is here! What range maps don't show us, Whimbrel migration

I can't believe summer is winding down. It feel like just yesterday Sonia and I were moving into our new LA digs! Though it has taken a bit of time to adjust to car culture and the hoards of people EVERYWHERE, I think I have established some form of birding and photography pattern that will permit me to enjoy the influx of birds that fall migration will bring to Southern California. So, without too much more mucking around, let me tell you what I was thinking about this past week while birding out and about. 

Birders are well familiar with distribution or range maps. These graphics show generally where a particular species occurs at what time of year. Take for an example the range map for Whimbrel. 

From this, we can see that Whimbrels nest in the extreme northern latitudes and winter in more southerly locations, notably along the California Coast, Gulf Coast, and southern half of the Atlantic Seaboard. Clearly, the bird does not magically translocate from one end of the continent to the other; This is suggested by the yellow shading which roughly designates major migration routes and stopover points. This map effectively communicates what the population of Whimbrel is generally doing at various points in the year, but it does not do justice to the incredible feat that is Whimbrel migration. For this, we need to look at the migration traces of individual birds, and this is precisely what advances in bird tracking now permit us to do. Take for example this slice of tracking data from 4 particular Whimbrels.

From this we can see some representative migration routes. The routes shown here, particularly the nonstop, 4000-mile oceanic segments, do far more to inspire our awe than a traditional range map. Prior to obtaining these data, we might have mistakenly assumed that Whimbrel migrated to South America via Central America. This overland route might make sense to our land-based human sensibilities, but it appears as though at least some Whimbrel exercise an unexpected and lengthy oversea route to reach their South American winter destinations. Range maps certainly have utility in conveying where a particular species can be broadly found, but they less effectively communicate how the individual birds move between the regions as indicated on the range map. This is where tracking data will provide invaluable. Coupled with real time range maps as generated in eBird, we are likely to glean much new and interesting information about bird distribution, movement, and migrations. It should be very exciting!

Whimbrel - Numenius phaeopus
Malibu Lagoon, Los Angeles County, California, 8/9/15
Canon 500mm f/4 IS v1 + 1.4x III on EOS 7D2
1/2500 at f/5.6, ISO 800, Manual mode

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