The Fen out by Happy Isles, at the east end of Yosemite Valley, is perhaps the most diverse and interesting habitat in Yosemite Valley. From sunny scrub to shadowy forests to well-irrigated wetland, it's all there. Being wet, white alder grows in abundance, which attracts the Red-breasted Sapsucker (Sphyrapicus ruber). With their thin bark, alders are an excellent choice for a drink of sap, so the Red-breasted Sapsucker is a common sight in the Fen. There's one alder, well worked, where I frequently see them. Yesterday (August 10), in between programs, I decided to wander the now-dry perimeter of the Fen to see what I could see.
The sapsucker is an amazing engineer. Scientist have tried to figure out how it makes the sap flow, but they've never been able to replicate it. Some believe that sapsuckers have some sap anticoagulant in their saliva. If you grew up in Vermont, like I did, you'll immediately contest that we do know how to make sap flow. The entire maple syrup industry depends on it. That is the nutritionally poor xylem sap. That's why we have to boil it down so much to get anything worthwhile out of it and why you can't harvest it all from most species of tree (because in most species the sugar content is so low). The sapsuckers can't drink gallons of sap, so they need to feed off the phloem sap from the tree's growing layer, which is rich in sugar and amino acids. But trees are designed to heal when wounded, just like us. The phloem sap typically dries quickly into a hard, dry scab. But not if the sapsucker opens the hole, sort of like what happens when a mosquito bites a mammal.
Anyway, wandering back further into the fen into the dense tree cover, I saw a Red-breasted Sapsucker on a different alder tree. Always a pleasure, but as I say, a common site. I stopped to watch for a while and suddenly, in come three hummingbirds. They were silhouetted against the sun, but based on size, I believe they were Anna's Hummingbird (Calypte anna). Two of them flew beak-to-beak in an undulating up and down flight, each oscillation taking in about 2-3 feet. Mostly though, they focused on what they had come for: drinking sweet sap from the sapwells created by the sapsucker. After a time they left and the sapsucker returned. Then the sapsucker left, and at least one hummingbird came back and so on.
It turns out that many species of hummingbird will horn in on sapsucker sapwells [1,2], a fact that was noticed at least as early as 1891 with the observations of Frank Bolles . Interestingly, ornithologist Laura Erickson, working in Wisconsin, found that Eastern Phoebes, Ruby-Crowned Kinglets and other birds also drank from the sapwells when the sapsucker rested. The hummingbirds, however, would chase off any bird other than the sapsucker. Since hummingbirds eat less than phoebes, in protecting its food source, the hummingbirds were also doing a favor to the sapsucker . Others have documented hummingbirds following sapsuckers, specifically the Yellow-bellied Sapsucker being followed by the Ruby-throated Hummingbird . It certainly seemed to me from this observation, and one later in the day (which I'll get to next), that the hummingbirds were on the sapsucker's trail.
So that was a pretty great sighting and I continued to wander, finding bear tracks and poop all over and eventually making my way back to the Happy Isles Nature Center to give a Junior Ranger Walk. We began our walk and as we approached the Fen, I looked and there was a Red-breasted Sapsucker on a white alder! I did an emphatic "Shhh" with my finger and the kids crowded around. The poor sapsucker was on the tree looking like it was suffering from heat exhaustion. On the trunk, it's beak wide open, it stood still as a statue, panting off the heat of the near-record 97-degree day (according to the Happy Isles weather station). In its torpor, it was reluctant to move and all the kids got a nice long look. So then I started explaining how they feed on the sap and that sometimes hummingbirds will also feed from the sapsucker holes. And right on cue, in flies the hummingbird!
The kids were also in torpor from a day out in the 97-degree heat, but when I asked if anyone besides me thought that was amazing, all the hands went up. They were, however, less than convinced when I told them I would, without hesitation, trade twenty bear sightings for what we had just seen.
This is a deep chain. When we enjoy columbines and scarlet monkeyflowers and other hummingbird-pollinated species, we don't think that they depend on flooded fen or a rushing creek miles away. But think about the life of a migratory hummingbird. It wants to show up in time to drink all the nectar from those flowers it loves, but it can't plan its trip by pulling up the Yosemite Scarlet Monkeyflower Webcam to see if they're ready to bloom. It has to show up early enough to catch the season, but if it's a late bloom, what happens? The sapsucker provides the food source to tide the hummingbird over through the lean times. So if a creek dries up, you lose the water-loving alders (and say something else happens to lose the deerbrush like, say, it just gets too warm). If you lose the alders and deerbrush that the sapsuckers depend on, there are no sapsuckers to make holes. If you lose the sapsucker holes, there's no fill-in food supply and you lose the hummingbirds. If you lose the hummingbirds, you lose the scarlet monkeyflowers and columbines.
Photo Credits and Sources
Photo of the red-breasted sapsucker by Kevin Cole via Wikimedia Commons and the photo of the Anna's hummingbird is by Alan Vernon also via Wikimedia Commons
1. All About Birds: Red-breasted Sapsucker
2. "A partnership that works. Sapsuckers and Hummingbirds" on Journey North.
3. "Ruby-throated Hummingbird Observed Following Yellow-bellied Sapsucker: Evidence for Keystone Bird Species in Northern Hardwood Forests," by David Flaspohler and David Grosshuesch, in The Passenger Pigeon, vol. 58, no. 3 (1996); download PDF