Field Journal #2- Physiology

Date: March 6, 2019
Time: 2:00 - 3:45 pm
Location: Shelburne Bay
Weather: The weather on this bird walk was fairly cold, with temperatures dropping to about 10-12 degrees. There was a light snow falling for the majority of the time, with fairly consistent cloud coverage (blocking the sun).
Habitat: I walked through the forested area in Shelburne that is adjacent to the bay. While I started out traversing the trails, a lot of my exploring was done off of the path.

The species that I observed during my bird walk utilize various evolutionary and ecological tactics in order to stay warm and survive the Vermont winter season. Although I did not necessarily observe these behaviors and processes directly during my time at Shelburne Bay, there is an ample amount of research and studies that provides insight into these birds’ winter lifestyles.

During my walk, I saw a really large abundance of American Robins (at least ten were gathered in the first few trees upon entering the forest), which allowed me to undertake thorough observations and think a lot about their winter behaviors. I noticed that some of the stationary robins that were perched upon a branch seemed very large from where I was standing, at least relatively to the robins that I see in other times of the year. Upon investigating this observation after my bird walk, I found out that robins often will fluff their feathers to help retain body heat. I found that fluffing up feathers increases the air next to the body and thus offers more protection from the cold. The composition of the Robin’s feathers also plays an important role in their winter survival, as they have a dense layer of down feathers close to the skin, which trap air and act as an excellent insulator. They have other layers which exist on top of this down feather coat, which further helps in separating the cold external air from the body heat that is being produced. During my time at Shelburne Bay, I witnessed two different robins eating small morsels of food (they looked to be some sort of berries). Consuming calories definitely assists in keeping the birds warm as it increases fat buildup as well as causes a rise in body temperature. While the other robins were not seen to be eating any food, they did seem to be moving around quite a bit- even when I was standing still and hidden. The robins kept sporadically flying between various trees, often moving as a group. Perhaps this movement was a foraging tactic, or maybe the intermittent movement helped them keep their body temperatures elevated. American Robins, like many other birds, also rely on each other for heat through roosting and cuddling. In very cold temperatures, Robins can stay close together to share body heat as well as seek protection from other weather factors (ie. snow, wind). While I did not see a lot of direct contact between the Robins that I observed, I did notice that there was a very large group of them which stayed in very close proximity the entire time I observed them- a behavior which I don’t often see when I observe a robin or robins.
During my time at Shelburne, I also saw a single Barred Owl perched on a tree very close to the edge of the forest. As I approached the owl, I noticed that I was able to get extremely close without him moving or fidgeting. As he stared me down from atop his branch, I wondered how owls are able to stay warm during the winter season- especially considering they are such independent birds. Much like Robins, I figure, Owls have a very particular feather composition that allows them to insulate their body heat effectively. Barred Owls, along with other members of the Strigiformes order, have a fluffy layer of feathers that extends all the way down to their legs and toes. They also have thick pads on their feet, which allow their extremities to remain warm during low temperatures. Due to the lack of wind that was present during the time at which I observed the owl, he was able to stand upon a tree branch that was relatively exposed to the conditions that traveled across the nearby field. I assume, however, that if wind and precipitation were especially strong, the owl would have seeked shelter behind an on-ground object or a denser, more internally-located tree.
Even though I did not directly observe or notice such behaviors, I know that there are other tactics which these birds most likely partake in to stay warm during the winter. The countercurrent exchange between birds’ body and legs, for example, allows for birds to deliver heated blood to their internal organs, and reduce blood flow to extremities without risking frostbite. Birds can also tuck their legs/feet into their feathers to shield bare skin from the cold. Many birds also have physiological responses to cold, such as shivering, entering a state of facultative hypothermia/torpor, etc. These types of physiological responses help birds to control metabolic rate and generate body heat strategically. Birds often enter a state of torpor or hypothermia at night, for example, as a method of conserving energy for an extended period of time. This involves reducing metabolism and shutting down certain systems so that less energy is required to maintain a proper amount of heat.
Because the Shelburne Bay park is such a densely forested area, I saw an abundance of snags that were distributed throughout my entire walk. By the time I was only a few minutes in, I had already counted well above ten snags/dead trees. I came across various types of dead trees, all of which could definitely be potential habitats to birds and other wildlife. Where the trail opens up right at the edge of the forest, there are several small dead trees that lay across the ground and form a jumbled mess of branches and brush. When I first spotted this scene, there were at least six American Robins that were seeking shelter in there. As I continued to walk, I found numerous snags that were standing up right. Most of these types of snags that I observed had various holes and cavities in them, either being naturally formed or formed from wildlife/birds. I noticed that the taller snags often times had several holes distributed up the length of the tree trunk at varying elevations. This, I assume, could be due to the same species of birds seeking different shelters or areas to forage for food. I also noticed that the thicker snags had larger holes that appeared to be more suitable to fit a bird or creature that is greater in volume. I knocked on a couple of these trees to see if any organism poked its head out, but I did not find any sign of life when I did this. Although I did not see any birds physically in the snags/cavities, these structures are very vital aspects of many birds’ lifestyles. Birds, and other small animals, can use snags for nests, foraging, roosting, and perching. Because of the dead/hollow nature of the trunk and branches, snags are excellent resources for birds to excavate and create fairly intricate forms of shelter. Snags also are home to many sources of food that are consumed by birds, including insects. Perhaps I would have seen more activity around the snags and cavities if I visited the area at a time in which birds were awakening or settling down for the night (dawn or dusk), which I will keep in mind for my next outing.

Publicado el marzo 7, 2019 09:22 TARDE por haleyferrer