Field Journal #4: Migration

On Saturday, April 3rd, I went into Rock Creek Woods in NW DC from 2:00-3:00 pm. It was 65º and sunny with no wind. These woods are dense forest made mostly of deciduous trees with a few coniferous trees scattered throughout. The woods have an area of about 2.7 miles so for a city forest, it’s a large swath of land. In these woods, I observed an American Robin, Northern Cardinal, Downy Woodpecker, and Pileated Woodpecker. On Monday, April 6th, I sat in my backyard from 2:50- 3:30 pm. My neighbors have a feeder that many city birds come to, and there is a large deciduous tree next door as well as many shrubs in surrounding area. The weather was 70º, and very sunny with no clouds in the sky. There was a light breeze. I observed House Sparrows and a Mourning Dove.
The year round species I observed were House Sparrows, Downy Woodpecker, Pileated Woodpecker, and Northern Cardinal. These birds could be non-migratory for a variety of reason including that DC does not get very cold in the winter, and I believe this winter it did not even snow. So, it could be energetically efficient not to migrate because it stays warm here and there is not a lack of food or resources. I think the sparrows rely on bird feeders and tourists for food in the winter because I have only observed them in the cityscape and not in the forests. The cardinals and woodpecker rely on insects and seeds to survive, and given the warmth there could be insect living in the trees still. The cardinal most likely relies on seeds from rodent droppings or twigs to survive and probably looses wait to compensate for the lack of food.
The only migrant I observed was the Mourning Dove, and it is a facultative migrant in DC. According the Cornel Bird Lab, Mourning Doves in more northern states will migrate to southern states, Mexico, or even South America. However, given that DC is a central district, the doves are facultative. A reason they could be migrating is that their foods are not available during the cold, or that the migration is not very intense, and there is more resources in the south. Their migration depends on if the expending the energy to go south is worth the resources or if staying for the winter is more efficient. A common wintering ground for them is Texas, so I calculated the distance from DC to Dallas TX, and it is a 1,328.2 mile trip one way, and a 2,656.4 mile round trip migration.

Publicado el abril 7, 2020 05:10 TARDE por iadeslaw