grady_jakobsberg's Journal

The weather today was a balmy 18 degrees with about 60% cloud cover at 9 am (we walked until 10:30 am). We left the Davis Center circle and walked down to Centennial woods, taking a short route into the woods and back over the hour and a half walk. We walked through a mix of urban environments (prior to the woods), and coniferous and deciduous forest.

The first thing we saw was a flock of about 14 Red Crossbills flying over the parking lot. They could be returning from a short nonbreeding winter season in more southern states - the main strategy that migratory birds use to survive the winter. However, I think most of the birds we saw today were year-round residents that had their own ways of handling the cold. We saw many smaller birds with their feathers fluffed up into little balls, such as the Dark-eyed Juncos who were perched in a dense shrub, likely to stay warm. Most of the birds we saw were in areas of Centennial Woods dominated by coniferous trees, whose needles provide extra insulation compared to the leafless deciduous trees. They were concentrated in large groups there - walking through we would hear the calls of 10 or more different birds who were likely staying together to work together in finding food. This highly populated area had plenty of snags and cavities - valuable resources for staying warm in the winter (more on that later). There was also evidence of squirrels pulling apart pine cones for food, which birds likely scavenge afterward because that is a food source they wouldn't otherwise be able to get at. Birds rely more heavily on fruit, seeds, and nuts during the winter because many of the insects they eat during the summer aren't around. We saw several different species, including the American Robin and Darke-eyed Junco, eating shriveled up berries that had fallen off various shrubs.

One of the most interesting things we saw today was a Barred Owl swooping away in the canopy. We didn't get a great look at it, but a small murder of American Crows followed soon after, squeaking loudly at it to move it away. I could imagine that some smaller birds are more at risk of predation during the winter from larger raptors and birds of prey because the lack of foliage leaves them more vulnerable and many of the other food sources have migrated south. That is why mobbing the predators in the way the American Crows did to the Barred Owl is an important way to fend off predators.

Mini-Activity: Snag Watch
Over the course of the walk, I saw about 15 different dead trees with cavities. They were in various states of quality - some trees were very rotted and the cavities looked to be unoccupied and falling apart. Other trees, particularly white pine, still had bark and the cavities looked to have been made more recently, evidenced by cleaner wood around the cavity entrance. Some of them had blong shapes, showing they were made by Pileated Woodpeckers. In the area we walked through that had a lot of birds, we heard a number of different species that likely used some of the surrounding cavities, including Black-capped Chickadees, White and Red-breasted Nuthatches, Tufted Titmice, and the Barred Owl. Since most of these birds aren't capable of making their own cavities, there is aggressive competition for the best sites. We didn't see any birds going in or out of cavities, but I would bet given the limited nature of them as a resource, most of the cavities I saw were occupied (except for the ones on overly rotted trees). In the winter, they're primary use is roosting to stay warm and protected at night, but during the breeding season they're main purpose is for nesting.

Date - March 21, 2021
Start time - 9:30 am
End time - 11:00 am
Location - Burlington Waterfront along the bike path
Weather - temp: 45° F, wind: 2-5 mph, precipitation: none, 0% cloud cover
Habitat(s) - sandy/rocky shoreline, urban, and some marsh

Walking up the bike path to meet the group at Echo, the first thing I noticed was a couple of Northern Cardinals calling back and forth at each other across the path. As I listened, I picked up on small differences in their calls as they went back and forth - namely differences in the length of the long "what" notes at the beginning of each call. I'm not sure what this means, but it was clear they were communicating over something. I also heard a lot of Canada Goose calls as they flew overhead in V formation in groups of 10+. I believe they honk in an attempt to keep the V formation together, which makes the long migratory flights less energetically costly for the group as a whole.

Two species that I saw a lot of today were Mallards and Ring-billed Gulls. I find it interesting that in some species like the Mallard, the plumages of males and females are dramatically different, but in other species like the Ring-billed Gulls, the plumages of males and females are practically identical. Male Mallards have a very distinct iridescent green head and females are mottled brown across their body. This sexual dimorphism is likely because the males have to attract females with their elaborate coloration - which could be explained by either the handicap principle or sexy son hypothesis. Mallards form breeding pairs in the fall and then migrate together, only parting ways after breeding season. This is something I observed today - all the Mallards I counted were in even numbers.

Ring-billed Gulls on the other hand look exactly the same for males and females. There is likely some type of coloration in the plumage that their ultraviolet-sensitive eyes can pick up on that we can't see. There are only a couple of similarities between the plumages of these two species. They both have black wing-tips which are colored with melanin to provide better structural support. They also both have featherless legs and feet, instead, they have a scaley material that provides better protection for all the uses of their feet. Countercurrent exchange allows them to maintain a warm body temperature despite a lack of insulation in their feet.

Many of the birds I saw today, mainly the ducks, gulls, and geese, were sitting in the water along a part of the shore where the surface ice was melted. Since there were a ton of them in a very shallow area, my guess is that they were simply resting during migration. This is the time of year for it (given circannual rhythms) and it was clear they weren't there to forage for food. Many of these species, such as Canada Geese, will travel with other species during migration, so it makes sense to see such a diverse group doing so. My only question is why they would be resting during the day rather than at night.

Mini Activity- Spishing:
We scared away a few Common Grackels and American Goldfinches with our spishing. While the sound can stress them out, birds are also often curious about it. Black-capped Chickadees particularly can be interested in the sound, and many other species tend to form mobbing groups around them. Small birds will flock around the sound to see if it is coming from a potential threat.