Assessing Some Key Approaches Used to Monitor and Study Populations of Birds

Abstract

Efforts to monitor birds and determine their distributions often make assumptions that allow for inference into parameters of interest but necessitate that potentially confounding factors be ignored. In any scientific endeavor it is fundamental to assess assumptions to confirm that more is gained in inference than is lost in simplification. In this dissertation, I use data collected in and around Tuskegee National Forest (TNF), Alabama to test assumptions of bird monitoring programs, sampling protocols, and models of distributions. Many monitoring programs assume the number of animals detected is strictly a function of the number of animals present. However, climate change may be causing birds to breed earlier, thus systematically changing bird vocalization and violating the assumption of constant detectability. I showed that if the breeding date of the bird community shifted earlier by one week, migratory birds will become less detectable during June. Further, the change in bird detection was not correlated with trends in abundance calculated using data from the Breeding Bird Survey. Next, I assessed assumptions related to assessment of habitat associations of birds. Many studies designed to predict or examine distributions of birds assume that birds choose habitat using broad scale information such as cover-type. This assumption is violated if birds choose sites using criteria other than land cover or within urban areas that are not adequately described by cover-type alone. I tested whether species ecology and urbanization affect Alabama Gap Analysis Program’s (GAP) accuracy when predicting distributions of birds. GAP performed best when predicting distributions of insectivorous birds that do not nest in cavities and within TNF rather than Auburn (a close-by urbanized area). I also tested whether addition of fine-scale habitat information increased inference into habitat use of migratory birds wintering in TNF. I found that occupancy models were improved by addition of fine-scale habitat variables. Finally, I assessed the assumption that birds retain the same habitat associations throughout the breeding season. I found that models which incorporated movement between sites outperformed models that assumed constant occupancy throughout the breeding season. The results of my studies should guide future studies of bird populations and distributions.