Field Journal #5- Reproductive Ecology and Evolution

Date: April 22, 2019
Time: 7:30 am - 9:00 am
Location: Intervale Trails
Habitat: Forested area that hugs a lot of edges (due to the farmland and fields in the area). The central area of the forest was completely flooded, with a couple of inches of stagnant water sitting on the forest floor.

During my bird walk this morning on the Intervale trails, I observed many different species of birds- most of which were exhibiting some sort of behavior that seemed to be related to mate/nest selection or territorial defense.
The first bird I came across was an American Robin, who was scurrying across the trail carrying a large earthworm in his bill. I assume this bird that I saw was a male who was spending his time foraging food and bringing it back to his female breeding mate. This is especially likely if the female was elsewhere building the nest, as they are the primary nest-builders. After I saw the first robin, I heard/spotted another one in a nearby tree. This individual was making a distinctive robin “yuck” call, and I presumed that she was the female of the pair communicating with the foraging male. Throughout my walk, I saw other American Robins and heard their song repeated quite frequently from different locations. These singing robins were most likely repeatedly belting out their song as a means of trying to attract a breeding mate or defending the territory which it had established for its nest.
The next bird I recorded was the Tufted Titmouse, who I heard very clearly but was unable to spot (as there was a significant amount of flooding which made the area difficult to traverse at points). I also may not have been able to spot the individual due to the nature of its nesting habits and locations. Tufted Titmice prefer to nest in tree holes and cavities, as well as artificial structures (i.e. fence posts, metal pipes). Because these nests are often very hidden and enclosed, it makes sense that I would only hear the titmouse’s call. The call that I heard very well could have been coming from a male who was defending breeding territory.
While continuing on the trail, I heard several winter wren songs coming from the same general location, and was able to spot one through my binoculars. They were singing their complex song very loudly and somewhat incessantly as I walked. This behavior seemed to be very indicative of breeding mate selection and/or territory defense. Because I heard more than one winter wren singing simultaneously, there could have been a male to male conflict in regards to territorial dispute.
I saw several black-capped chickadees throughout my walk, and they seemed to exist in pairs or small groups every time I noticed them. I was not able to locate any possible nests or cavities that were occupied by the chickadees, however I assume the areas in which I saw pairs of chickadees were somewhat close to their possible nest-site for the breeding season. Most of the chickadees I saw were only a little bit above my head level, which makes sense considering they often do not nest higher than a few meters. The nests, which are built by females, usually exist fairly deep into an excavated cavity and include a covering of natural materials, therefore they are somewhat inconspicuous when walking on a trail.
There were several three northern cardinals that I found during my walk, 2 of which were males and one which was female. One male and one female seemed to be foraging in thicket very close to the ground. The other male was found perched on a branch a couple of meters off the ground. While the male and female who were foraging did not make any noise, the perching male was singing the “cheerio cheeri-ie” song quite loudly. It seemed as though this individual was trying to find a mate or defending its territory (perhaps from the two foraging cardinals below). At one point, the foraging male cardinal took off and flew many trees down, with the female following him a few seconds later. Due to this behavior, I figured that the two individuals were, in fact, a breeding pair, and they were working on foraging nest materials or trying to find suitable nest sites.
I saw two brown-headed cowbirds together, hopping about in a mess of branches and vegetation on the forest floor. One was a male and one was a female, which can be seen in the picture I uploaded to my iNaturalist observation. The two seemed to be foraging for seeds or insects in the soil, and they never seemed to stray too far apart. The pair, which I assumed to be a breeding pair, was not making any noise (neither songs nor calls). I assume that they were so quiet because they did not have any vital territory to defend nor did they need to communicate in such close proximity. Because the Brown-headed Cowbirds lay eggs in other birds’ nests, they did not have a territory or nest site in which they had to spend energy defending.
I heard one Mourning Dove throughout my walk, who let out a strong and frequent song in the distance. I never spotted the source of the song, but it sounded as though there was only one individual. I know that Mourning Doves may nest at higher elevations than some of the other song/perching birds I observed, therefore it makes sense that I heard the call coming from a farther distance.
I saw an abundance of Song Sparrows during my walk (about 5), and heard more coming from deeper into the forest. All of the Song Sparrows which I observed seemed to be sort of jumpy and very mobile. It was hard for me to get a good look at one before it took off for another nearby branch. This behavior, to me, seemed like the individuals were looking for something- whether it be a suitable nesting site or food/resources for the breeding pair and offspring. There was one stationary male (the one that I have pictures of in my observation), who was fairly stationary and loud. He remained perched on a branch and allowed me to walk fairly close to him, as he loudly sang the entire time. Due to this behavior, I assumed that the male was defending potential territory or trying to find a suitable mate.
I saw two White-throated Sparrows during my outing- one which I assumed to be male and one female. While I was not sure about the physical distinction between male and female White-throated Sparrows at the time, their close proximity and peacefulness in each other’s company made me think that the two were not competitors. The two of them kept traveling between the ground and low twigs/branches of a nearby thicket. Because White-throated Sparrows build their nests in low elevation areas with dense vegetation, I presume that this pair was a breeding couple who was working on constructing a nest for the upcoming season.
Many birds have very specific and unique nesting characteristics which are complementary to their life history traits (i.e. diet, habitat, foraging/behavior, etc.) Out of the bird species that I observed this morning, three with some of the most distinct nesting patterns (in my opinion) were the Brown-headed Cowbird, the Winter Wren, and the American Robin. While I observed all of these bird species in the same general vicinity, their requirements and preferences for nesting are quite different. Brown-headed Cowbirds are very unlike the other species that I observed today, because they are “brood parasites”- meaning they do not build their own nest, but rather lay their eggs in the nests of other species. Female cowbirds will search for females of other bird species that are in the process of laying eggs. When she finds a host that is deemed suitable, the female cowbird will sneak into the host nest and replace one of the existing eggs with one (or more) of her own. Some popular nests in which the Brown-headed Cowbirds lay their eggs include the Red-wing Blackbirds, Ovenbirds, Yellow Warblers, Song Sparrows, etc. The types of nests which these host species occupy are not very similar, and range from nests on the forest floor to treetops. Usually, the Brown-headed Cowbird will select host nests that contain eggs with smaller volume than their own. This can result in cowbirds quickly lowering the success and wellbeing of their host individuals upon hatching. American Robins, on the other hand, build their own nests for the breeding season. Much like the female Brown-headed Cowbirds choose the host nest, female robins decide where their nests will be built. They usually choose nest sites on horizontal branches that are hidden beneath a layer of dense vegetation. Females are also in charge of building the nest, which they do from the inside out by pressing dead grass and twigs together to form a cup-shaped structure. Winter Wrens are another species of bird with nesting behaviors that I find quite interesting. Winter wrns do make their nests, however the shape and placement of these nests are different from the American Robin/ The Winter Wrens nest are more dome-shaped/globular, and offer protection on almost all sides. To obtain a maximum amount of coverage, wrens will often build nests in dead trees and cavities. Unlike the Brown-headed Cowbird and the American Robin whose nest site is scouted out and built by females, the building of Winter Wren nests is done by the males. The males will build several nests in a season before showing the nest options to a female who will choose which one to use. Nests usually exist anywhere between ground level and 20 feet above the ground.

Mini Activity:
When I sat quietly in one spot in the forests surrounding the Intervale Center, I heard many different species singing/calling from all different directions. The chaos and volume of all the different competing sounds was sort of mind-blowing, and it took me awhile to discern any individual species. Once I let the symphony of bird songs sort of settle in my brain, I was able to focus in on one species at a time and try to identify them. I heard several winter wrens that seemed to be about 20 yards in front of me. I could tell that they were different individuals due to overlapping songs as well as slight differences in vocalization patterns. Almost immediately in my ear, I heard the very recognizable song of the Song Sparrow, who in actuality ended up being a lot farther than I thought based on audio alone. Across the marshy area to my right, I heard a woodpecker drumming away, however I was unable to ID it based on the drum beat alone. From very far behind me, I heard an individual making a lengthy call that comprised of crazy combinations of whistles, trills, and clicks. While I never was able to find the bird and confirm, the chaotic nature of its song seemed like me to be coming from a European Starling. There were a couple of other songs in the distance that I simply could not ID at the time, due to them blending in with the songs of other birds or me simply not recognizing them. I wrote down some notes that came from the same general location of the woodpecker drumming- which I illustrated as short of short staccato notes that are evenly spaced. Upon looking up the sound for the Downy Woodpecker, I realized that those short squeaky calls could have been coming from the same individual that I heard drumming.

Publicado el abril 22, 2019 07:35 TARDE por haleyferrer