Where's the Water?
The large flock of sparrows, predominantly white-crowns, that arrived in the fall stayed through much of the winter. It was surprising to me because the fall and winter were extremely dry, with only a couple of measurable rain events. The sparrows mainly feasted on various dried grass seeds in the floodplain. But where did they get their hydration? Outside of a few folks putting water out for wildlife and stock, the only natural water sources I knew of were two miles south and four miles north. The river didn't flow all winter. Yet, the core of the flock I was following stayed in a dry grassy area in between.
One late afternoon, on a sparrow walk, a small group of us noticed sparrows and towhees flying up to the side of a small cottonwood tree. Further investigation revealed a wound where a branch had broken off and it looked damp. One of us decided to check it out, and sure enough, it was wet. This was at a time when we hadn't seen any rain for weeks.
Lincoln's Sparrow using a cottonwood drinker
I started looking for other wounds in cottonwoods that might exhibit the same phenomenon as the one we found. In one day I mapped ten locations that either had active use or looked promising. Many of the active ones were on the interface of the cottonwood trees and the grassy areas. Some of them were virtually little bowls of water with water stains running down the sides of the trunk. This all during one of the driest times we've had since monsoon.
Cottonwood is known for its brittleness and how it sheds branches on a regular basis. They are also known for providing habitat for cavity-nesting birds and owls that take advantage of hollows that form in some cases. In the past I had assumed that the wet-looking streaks from such wounds was a sticky sap. I was amazed when I looked closely into some of the wounds and found shimmering pools of water whose only source could be from the subsurface river water that the trees continued to draw upon, even during their dormant winter sleep. A quick smell and taste revealed a strong "wet wood" scent and flavor. I'm assuming that is a couple of steps up from a murky pool that cows have been urinating and defecating in.
These little reservoirs clearly provided enough water to sustain one of the largest flocks of white-crowned sparrows I've experienced, and during a very dry fall and early winter. When we did get some rain, the activity around the wounds would drop off. It would then pick up a few days later as the rest of the land dried out again.
Eventually, the white-crowned sparrow population began to drop off towards the end of winter. Knowing that they had a steady supply of water makes me confident that they moved on for other reasons.
I will never look at cottonwood trees the same again.