Saturday, March 17, 2012

A Spectacle of Swallows

The field season has kicked off once again, and I spent the past ten days with the 2012 Great Basin Bird Observatory (GBBO) crew around Blythe and Yuma (Cibola and Imperial NWRs).  The beginning of the field season is the most difficult work, clearing trails and scouting plots to ensure that surveys go smoothly.

Resting on a small trail my crewmate and I carved through an arrowweed stand (Photo by Brandon Breen)

During this first tour, the crew spent several nights camping at Fishers Landing on Martinez Lake.  The campground itself was nothing to write home about, but the birding in the area was pretty good.  One thing we noticed at our campsite was that streams of hundreds of Tree Swallows would pass overhead each evening.  This was no surprise to any of us who had spent a spring along the Colorado River before, as migrating streams of swallows are a common sight out here.  One evening, though, we went up to an overlook point to scan the lake and we were impressed by the number of swallows streaming over the water, swirling over the marsh, and gathering in flocks high over the lake.  Eventually, all the swallows gained elevation and streamed into the masses high in the sky.  Numbers increased rapidly, from a few thousand to more than 20,000 as we stood and watched, estimating numbers repeatedly.  The ball of swallows moved through the sky with the liquidity of smoke, merging and splitting, climbing and shifting as the light dimmed.  Eventually, a few hundred birds broke off from the flock, diving almost straight down toward the marsh before breaking at the last moment and settling into the cattails, preparing to roost for the night.  As more and more birds joined in the plummet to the marsh, they appeared as whirling vortices to the naked eye, like twisting pillars of smoke.  Soon the clouds of swallows had drained to nothing, and as darkness fell, and two Black Rails began calling from the marsh, we headed back to the campsite.

The next night, having heard from us the spectacle we'd seen, most of the crew took the walk to the viewpoint.  The swallows were out again, streaming over the water and building in flocks over the marsh.  Eventually the flock built to an estimated 50,000 birds, more than twice the size of the previous evening's flock, and twice as spectacular!

The swallows' marsh
The crew enjoying the swallows (Both photos above by Brandon Breen)
Watching the swallows spiraling down to roost

I've seen some fantastic migration events, with the raptor migration of Veracruz topping the list: a constant stream of Broad-winged Hawks, Swainson's Hawks, Turkey Vultures and others topping 250,000 in one day!  At Hazel Bazemore near Corpus Christi, TX, I've seen kettles over 10 and 20 thousand.  This sight of swallows gathering at dusk was equally spectacular to me as those kettles of hawks.  It occurred to me while I watched this that this surpassed any gathering of cranes in Arizona or New Mexico.  Why not have a March Swallow Festival?  After all, our count of 50,000 wasn't even very high--last year's high count was about one million, and that wasn't unprecedented.  In early March last year, I counted nearly 3,200 Violet-green Swallows migrating over Rotary Park in an hour and a half.  This is a regular phenomenon in this area--even researchers are beginning to look at it using radar.  I would like to see a time in the near future when wildlife enthusiasts from all over the country (the world?) come to the Lower Colorado River Valley to see the swallow migration!

1 comment:

  1. That sounds amazing Lauren. I usually start geeking out after watching just a dozen swallows fly over a pond in the evening--50,000 might induce cardiac arrest.

    It's lovely to read your reports on the listservs (and I believe you also helped me correct an eBird error I made). Thanks for all of your diligent work. I'm looking forward to hearing more about this most recent tour of duty.