What: It's FOY (first-of-year) season, and the skies are abuzz with the wing beats of our first returning migrant birds. Apparently, they didn't hear about our record-setting cold weather. I love the first flocks of vultures returning north. They come with the male red-winged blackbirds, the waterfowl (if only our ponds would thaw!!), and the courtship behavior of our over-wintering birds like chickadees.
I spotted this committee of vultures (see my post on collective nouns) over the St Joseph Cemetery on Archibald St in Burlington on Saturday afternoon. There were at least 15 birds.
Over the next few weeks we'll see more and more birds returning to the state. It's an exciting time of year - I'd love to hear what other folks are starting to see as the days get longer and (hopefully) warmer.
Bonus post: Just wanted to post a quick video I put together from that epic thunderstorm last night. For a better synopsis of conditions leading up to and during the storm, check out The Weather Rapport.
What: Last Wednesday and Thursday I paddled the Winooski River from Bolton Dam down to Salmon Hole in Burlington (about 30 miles or so). There are a couple of great paddling guides online (1) (2) that give a sense of what to expect from the conditions on the river, but do little to describe the sheer joy of getting lost in the meandering freedom of the Winooski's bends and folds. Only occasionally did the old span bridge or rumble of a semi's engine break remind me of the thin border of silver maples separating me from the faster pace of asphalt and clocks.
Ecological notes: I was particularly fascinated with the enormity and odd grace of the committee of turkey vultures that seemed to defy my cultural expectations of what a vulture should be (on Friday I'll post more about collective nouns, like committee, for animals). Wednesday evening I came to a fork in the river where it split around an island. I saw a turkey vulture circling low on the south stretch of the island and so I set down that direction. As I slowly approached, another turkey vulture landed on a gravel spit about a quarter mile down from me, followed shortly by three more. I tied up my boat and crept slowly along the shore line to get a better view. As I rounded the bend I was treated with a spectacular view of about 25 turkey vultures either sunning themselves on the rocks or perched up in the trees preening themselves.
In that late afternoon heat I wanted nothing more than to spread my own arms out and sun myself on the rocks with them. I couldn't help but wonder if that was the ultimate motivation for the turkey vultures' behavior. When I got back, Callan and I came up with a pretty short list of reason why we thought the vultures (and other birds) might do sun themselves. Here's what we came up with:
Kill bacteria by drying them out (they're detritivores, an animal that eats dead stuff, which is probably a source of all kinds of nasty bugs)
Kill other parasites, like taking a dust bath
Produce Vitamin D
Warm themselves up before going to bed
Warm themselves up to increase metabolic rate, digest food faster
Visual display of power to other turkey vultures
Dry off
I've also seen cormorants do this (see photo above), pelicans, and green herons. Some quick research shows that many birds do this, but their posture is different from the vultures and cormorants shown above. Indeed only a few others, like anhingas, storks, and other herons, do this standing up with wings spread. The ring-billed gull colony I encountered the following afternoon had about 300 individuals (plus a small handful of mergansers) all standing facing the sun, but with wings closely tucked in).
Some patterns in the list of birds that sun themselves standing up with wings out emerge: many are aquatic, they tend to be darker, they're carnivores, they're very large birds, they live longer than most birds, and most are in the stork order, Ciconiiformes. After writing this I looked up the order of pelicans (Pelicaniformes) to see if it used to be included in Ciconiiformes, and sure enough Pelicaniformes is often proposed as part of Ciconiiformes. What's even cooler and more surprising is that new world vultures (as opposed to buzzards and their old world kin) are close cousins of the storks. So if this behavior of standing up and sunbathing is monophyletic (occuring only in one evolutionary branch of birds), then it might be reasonable to assume it originated in a single ancestor of new world vultures, herons, storks, cormorants, and pelicans. The behavior might then serve a unique purpose among these birds.
I didn't find anything conclusive, but it looks like birds will sunbath for all the reasons that Callan and I came up with. A 1957 paper on the topic indicates that birds might also sunbathe socially; if one starts sunbathing then others will join her/him. I'm not sure what the primary purpose of sunbathing is for these birds, but I'll bet spending lots of time in/near stagnant water (for cormorants, herons) and eating carcasses (vultures) makes these birds susceptible to parasites so having a way to kill them would be good (maybe the black of a vulture heats their feathers up to a higher more lethal temperature).
Additionally, vitamin D deficiency can pose skeletal problems, making large body size a critical reason to sunbathe. Ciconiiformes and vultures don't migrate far, so in the winter they're not getting as much vitamin D as say migratory song birds might. Vitamin D deficiency prevents an animal from absorbing calcium from food. Prolonged deficiency (as with people in northern latitudes) can result in weakened bones that bend and curve under the body's weight (like the stereotypical bow-legged Eskimo). Sunning would be an effective way of producing vitamin D.
Another source says that warming up feathers "resets" their curvature, bringing them back to their most efficient shape, an obvious advantage for a turkey vulture, which spends most of its time soaring looking for food. But I couldn't verify this with any reputable sources.
Where: Winooski River, about 2 miles upstream from Richmond.
What: A couple of days ago, Fish and I paddled the 10 miles from Salmon Hole down to the Winooski's mouth at Delta Park. As the sun set we heard more and more beavers slapping their tails at us. The birds were out, but the heat made everyone a bit slower. This turkey vulture was standing on the bank and didn't seem to mind until I was downstream.
Our last few miles we paddled in the dark before setting up camp along the beach, with a sky full of stars over head. We woke up Friday morning to a pair of baby ravens making a ruckus, and then paddled to Burlington, ate breakfast at Skinny Pancake, and then leisurely made our way to the south end of Shelburne Bay, rounding out a 22 mile trip. The weather was hot, and the mosquitoes and deer flies were hungry and irritable. It hasn't rained in forever, so the Winooski River was about as slow moving and low as I've seen it. Good luck set in while on the lake, where we enjoyed a strong, favorable tailwind blowing out of the Northeast, and we were probably paddling faster on the lake with the wind than on the river with the lazy current.
Ecological notes: I was picking up a lot on different signs of old high water lines. We found a bank burrow from a beaver that was about 2' higher than the water. A beaver would only dig a den below where the water line would consistently be to ensure that the entrance was always concealed. Maybe a young one that wasn't expecting the water level to drop so much had made the bank earlier in the spring.
Other signs included debris lines of branches strewn along the banks at different heights and sand bars that were exposed on the downstream side of islands. One of my favorite signs was all the silver maple seedlings sprouting up at distinctly different terraces along the bank as in the photo above that shows two such terraces. My guess it that they correspond to two rain events. The upper "terrace" of seedlings being deposited first in a big rain storm. Rains could have washed loads of the seed crop into the river as it swelled. Seeds were deposited at the edge of the river, particularly on the inside of the river's turn (called a point bar, or erosional area, as opposed to the outside of the turn where water moves quickest, called the cut bank; cut banks usually have steep slopes as opposed to the slow sloping banks of a point bar).
Water level subsided and the seedlings germinated. Another smaller rain storm could have brought the water level up again, but not quite up to the level of the first surge. The next batch of seedlings are much smaller, many of which still had the dicotyledons (the first leaves that look more like bananas than maple leaves), the upper level seedlings had two to three pairs of mature leaves and thickening stems.
What: It's FOY (first-of-year) season, and the skies are abuzz with the wing beats of our first returning migrant birds. Apparently, they didn't hear about our record-setting cold weather. I love the first flocks of vultures returning north. They come with the male red-winged blackbirds, the waterfowl (if only our ponds would thaw!!), and the courtship behavior of our over-wintering birds like chickadees.
.JPG)
.JPG "Adult turkey vulture about to take off")
.JPG "Silver maple seedlings along Winooski River")