18 September 2008, Isabella Reservoir, Kern River Valley, Kern County, California
I observed an extraordinary massed bathing of Violet-green Swallows very early this morning. My attention was diverted from my daily search for freshly arrived autumn migrants to the big nearby pond, where the water appeared to be vigorously boiling. Upon closer inspection, I discovered that the normally dark water was being churned up by several hundred swallows, repeatedly striking the water's surface. With every strike, each little swallow sent a tiny jet or "rooster tail" arcing eight to ten inches into the air, shining brightly, ignited by the sun's first rays skimming over the hills.
With hundreds of swallows engaged thus, and with some birds striking several times like a stone skipping over the water, the water's surface seemed to sizzle and boil wildly, reminding me of how the surface of the sea appears when myriad small fish roil and thrash at the surface in their efforts to escape larger fish attacking from below.
The activity wasn't constant, but ebbed and flowed. Over the fifteen to twenty minutes that I watched, the hundreds of swallows alternated between swirling over the weedy shoreline, at all heights and distances, to gathering over the pond where they would gradually lower toward the water. The bathing frenzy began with only a few birds at first, then steadily increased until all the swallows were veering toward the water at a shallow angle and striking. Each swallow followed up its dip with vigorous in-flight shaking off and even in-flight preening.
Although I have observed swallows bathe in this fashion many times, it has never involved so many birds or produced such a spectacle.