April 8, Migration

April 8, 2020, 4:00-5:30p
Weather: Mid to upper 50's and sunny.
Location: The Intervale Center, Burlington VT
Habitat: Started in an urban area, moved to an heavily human-influenced forested floodplain. Very sandy soils, and sparse underbrush. Many deciduous trees, with plenty of large snags.

For this bird walk, I decided it might be interesting to return to my first birdwatching site from this class on the trails in the Intervale, and observe the changes between the winter and the beginning of the spring. The walk started off well, as I spotted a cardinal outside my window while I was getting ready to leave, and then a pair of blue jays almost immediately after leaving the house. I started by walking through a small graveyard which had some good bird activity. I saw a number of starlings, which are residents to Vermont, and a few robins, which are facilitative migrants. I have seen a couple of robins around Burlington this winter, but there seemed to be a lot out of them out today. Eventually I got down to the Winooski river, and my next fun sighting was a group of 4 common mergansers in the water, though they moved on before I could look too closely at them. There were a couple of other memorable moments throughout the trip, one being closely investigating a pair of noisy tufted titmice in some shrubs, as I feel I have only ever really seen them from afar. The other was a bird I was unable to identify, which really vexed me. I first thought it was the wood thrush we talked about in class today, but the coloration wasn't quite right. It looked a lot like a song sparrow, but much smaller than I picture a song sparrow being. The size reminded me of the winter wren, but it didn't keep its tail cocked in the same way.

When looking at migration, most of these species, including the other species listed in the observations, are residents or short distance migrants. The true residents need to be tough or resourceful enough to find food throughout the winter, need adaptations like the brainpower of a crow to find food, or the memory of a chickadee to remember where you hid it during the summer. Also, they are all birds that spend most of their lives above dry land, many of them reside in the forest, which may help keep them safe from some of the harsher winter conditions. Our longest distance, and only obligate migrants, on the other hand, were both waterbirds, the Canada goose and the common merganser; and it makes sense to fly south if your food source is going to be trapped under a layer of ice for 6 months. Others are somewhere in between, like the American robin, which generally migrate short distances. This also seemed to have an effect today, as I saw robins on many different occasions, though many were close enough that I didn't want to double count. It might make sense that there may be more robins here as the weather warms, or I could just be experiencing conformation bias. Either way, based on the birds we saw today, habitat type may be one reason for birds to migrate, as freezing temperatures can leave some waterbirds without many options.

Estimating the distances the birds had flown to travel here was challenging. I chose 4 that migrate at least a little bit: the Canada goose, the common merganser, the American robin and the song sparrow. None of these migrants have travelled very far yet, though the former 2 may have a long journey ahead, which is why to makes sense that we are seeing them here so early. Among the 4 species, I estimated that they had traveled a total of about 1500 miles to get here, though this number has an enormous margin of error.

Posted on April 9, 2020 01:11 AM by lucasferrier