PERCEPTION OF THE HORIZON PREDICTS BIRD ABUNDANCE BETTER THAN HABITAT PATCH SIZE IN A TIDAL MARSH SPECIES OF CONSERVATION CONCERN
Author: Hallie Marshall
Major: Wildlife Ecology
Graduation Year: 2017
Thesis Advisor: Erik Blomberg
Description of Publication: The Saltmarsh Sparrow (Ammodramus caudacutus) is a tidal marsh bird species facing rapid population decline throughout its range. A major cause of this decline is degradation and loss of breeding habitat, and thus there is a need to preserve coastal marshes in the northeastern United States. To do so requires an understanding of the habitat features that support robust populations. Previous studies have shown increases in Saltmarsh Sparrow abundance with marsh size increases. In other grassland bird species, habitat patches with low horizons are preferred to those with tall objects (e.g., trees, telephone poles, wind turbines). This study tests how the abundance of Saltmarsh Sparrows is affected by the maximum height of objects in the horizon of marshes. Abundance data were collected via point count surveys at 1,698 points from Maine to Virginia during the 2012 breeding season. At each of these points, a clinometer was used to determine the height of objects in the horizon. Using program R, we evaluated detection and site covariates to determine the model which best predicted the abundance of Saltmarsh Sparrows. Our study found that the angle to the maximum horizon, which considers a bird’s perception of its surroundings, is a better predictor of abundance than marsh patch size. We found that the highest abundance of this species was observed in marshes where the angle to the horizon was zero degrees, and at angles greater than 13 degrees the predicted abundance fell below one bird per point. This implies that perceived openness, rather than a large area, is selected by this species, and should be a prioritized marsh characteristic for the conservation of Saltmarsh Sparrows.
Location of Publication:
URL to Thesis: https://digitalcommons.library.umaine.edu/honors/275/