Field Observation: Migration

For this week’s journal entry, and given the current Coronavirus situation, I travelled to my grandmother’s house in Barrington, Rhode Island. It was April 4, 2020, and at about 4:00 in the afternoon when I began observing birds on her bird feeder and around her yard. The purpose of the visit was actually just to check in on my grandmother and spend some time with her outside, and at the proper distance. Once I started seeing how many birds were flying around her yard, however, I couldn’t pass up the opportunity to sit for a while and observe. The yard is very shaded with many large trees and bushes, providing plenty of habitats for many different bird species. More specifically, the habitat had a mix of tree cover and open grass, along with shrubs, bushes, and flower gardens. Along with this, since it was in a backyard, the area could also be described as residential and suburban. The weather at the time was about 50˚ with a slight cool breeze. Since it was around 4 o’clock, the sun was lower but not yet setting, but it had begun to cool down for the day.
I will begin by first listing all of the year-round residents for Rhode Island that I observed. These include the House Sparrow, Tufted Titmouse, Black-capped Chickadee, White-throated Sparrow, Blue Jay, Downy Woodpecker, and Northern Cardinal. Some reasons behind bird species remaining in one place year-round are that migration is energetically expensive, and if it is not necessary for the species to move around, they will refrain from doing so. Along with this, there is a high mortality rate during migration that can be attributed to inclement weather. If the reproductive output of a bird species does not offset the mortality during migration, then it is not advantageous in a biological or evolutionary sense. In terms of the adaptations utilized by year-round residents, they can be physiological or behavioral, both of which help an individual survive various conditions. These can include behaviors such as hypothermia or torpor, the act of extreme shivering to generate body heat in the winter or nesting in smaller holes in trees to stay warm. In order to be a successful year-round resident, birds must also transition to different food sources depending on the season. Birds that eat mostly insects and berries in the spring or summer may search for nuts in the winter instead, for example.
Some examples of facultative migrants that I observed on my most recent birding outing are the American Crow, American Goldfinch, Mourning Dove, American Robin, European Starling, Herring Gull, and Common Grackle. Unfortunately, I do not believe any of the species I observed are classified as obligate migrants. However, I have plenty of facultative migrants to discuss, meaning those species determine each year whether they will migrate. Most of the species listed above would be arriving in Rhode Island at this time of year, coming back from somewhere warmer where they spent their winter. Some specific examples would be the American Robin, which in the winter migrates to the warmer, southern states in the U.S., or the Common Grackle, which only migrates short distances within its range. In terms of environmental changes that cause these species to arrive back in Rhode Island around this time, the biggest factor would be temperature. A lot of these birds are not equipped to spend winter in the northern regions, but now the temperature is beginning to be consistently higher and things are starting to bloom. However, especially in Rhode Island and the northeast in general, the weather can still be quite variable in April, which could be a disadvantage of the birds arriving this early.
As part of the mini activity, I wanted to include the rough estimate of miles travelled by all of the facultative migrants I observed, since I wasn’t able to spot any obligate migrants. Using Google Earth to help me map it out, I determined that the migrants I listed in the previous paragraph travel a total of about 2,570 miles. Keep in mind that this is a complete estimate, however, and I also took into account that a lot of them are considered “resident to short-distance migrants,” so when given a range in their distances travelled, I leaned toward the lesser

Publicado el abril 7, 2020 11:24 TARDE por bethanysmith512