Print PagePopulation numbers of bird species associated with habitats characterized by intermittent disturbance have declined throughout North America (NA) over the last century. The loss of early-successional habitats due to the suppression of fire, abandonment of farm fields, and expanding urbanization play a major role in these declines. Although early-successional species are often assumed to be edge specialists at a patch scale, this may not be true at a landscape scale. Patch context, a theory which asserts that the structure and composition of a matrix surrounding a habitat patch will affect the biological processes within, may be an important factor for early-successional species. The Golden-winged Warbler (GWWA) is a Neotropical migratory songbird that relies on early-successional habitat to breed and is one of the most rapidly declining songbirds in NA. In Canada, the species declined by 79% from 1993 to 2002, and in 2006 was listed as ‘threatened’ under the Species at Risk Act. The objective of my study is to assess the effects of anthropogenic disturbance in the matrix on GWWA occupancy at multiple scales to better identify critical habitat. I used province-wide GWWA presence/absence survey data from 2008-2010 collected by Bird Studies Canada. These data were overlayed with a land-use map created by the Manitoba Land Initiative. Using ArcGIS, buffers were created around each point at 200, 1000, and 2000 m and the proportion of each land-use type falling within each buffer was calculated. I used generalized linear mixed effects models to determine the effects of anthropogenic land use on GWWA occupancy and density and Akaike’s Second Order Confirmation Criterion was used to select the top-ranking model(s).
Results/Conclusions
I found that the presence of GWWA was significantly negatively impacted by agricultural and urban land uses that fell within the matrix. These negative effects were present at all three spatial scales (200m, 1000m, 2000m), although the effects were strongest at the largest scale. At this scale, there is a threshold of 35% anthropogenic land use in the matrix above which GWWA are no longer present. Densities also significantly decreased as the proportion of anthropogenic land use in the matrix increased. This indicates that patch context is an extremely important factor determining habitat suitability for GWWA. Future management programs must consider the effects of the matrix and the scale when determining where to preserve or create habitat for the GWWA. Future research should address the mechanistic basis for these results.
