Field Observation 6: Reproductive Ecology and Evolution

Time: 3-6:30pm
Date: April 22, 2018
Location: UVM's Redstone Campus. Specifically in the front and back of WDW residence hall. 
Weather: Sunny, warm, felt like 70 degrees F. Actual 58 degrees F.
Habitat: Campus with open grassy areas, and small clumps of trees. Parking lots and buildings. More concrete and brick than grass and dirt.
Journal: At this time of year, there are many behaviors occurring that are related to mate selection, nest selection and territory selection. I have heard American Crow individuals cawing at each other, each round becoming louder and louder, faster and faster. The males yell at each other to be the more available and attractive partner to females. They are also defending territories by making themselves sound more menacing. I am also seeing Cedar Waxwings flocking in trees and descending to the grass in unison. That may be more for foraging, but they move around in flocks, perhaps looking for a territory for the summer? Some species are nesting on the roofs of buildings, while others are nesting in the tree tops or clumped in bushes. I think that a flocking bird such as the Cedar Waxwings would be likely to nest in the bushes so that they could stay close together, although I have not observed their nesting sites. The habitat requirements for nesting and territories vary among species because they have different group behaviors. The Waxwings move in flocks and are always together. Crows will forage in flocks, but for mating and nesting, will separate into their own territories.
I think that it would make sense that if a bird were singing extra loudly while defending its territory, it must have a prime territory and so it would be working extra hard to attract a mate to share it with. But it would also make sense that a female would see the prime territory and already be making a beeline to that male. That loud male may also be singing extra loud in order to appear more attractive and healthy to make up for the fact that it had a low quality territory. A large and prime territory would indicate that the male was healthy and able to defend a large territory, and win disputes more often- maintaining the territory. A weak or unhealthy male would lose more disputes and by default have a smaller territory.
A Bald Eagle is a very large bird. It would have to build its nest out of materials strong enough and in a place that would be able to withstand the weight of the pair, the chicks, the eggs, and the food. The adults may be 14ish pounds, so 28lbs of adult, maybe 3 eggs/chicks, so say 40lbs of bird total in the nest. Then the additional 20ish-lbs of a fawn for food, the tree or ledge that the nest was in would have to hold 60lbs of bird and food, and then the nest itself. It would need to be built in a strong tree that is older to be stronger, and less likely to be blown or knocked over. The nest would have to be built out of strong materials, unlike the twigs and grasses that might make up that of a Black-capped Chickadee’s nest. The Bald Eagle would be likely to use sticks and branches. If it were built in a tree, the Eagle might incorporate the live branches for stability. They would be likely to also line the nest with plucked feathers for warmth, as well as some grasses or leaves for cushioning too. The Eagles would have to search around the nest for these materials. The grass would be on the ground, feathers from their bodies, and then the branches and leaves from the trees around the nesting spot, or from the ground/fallen branches.

Publicado el 29 de abril de 2018 por esm398