Breeding bird community dynamics in a bottomland hardwood forest of east Texas

Conservation of bottomland hardwood forests throughout the Southeast is of great concern due to significant habitat loss and potential impacts on the complex biotic productivity occurring in these systems. Development and agriculture has suppressed frequency and occurrence of natural disturbances (i.e., floods, droughts, windthrow, fires, and hurricanes), fragmenting and degrading remaining forests and ultimately causing the decline of many forest-dependent bird species in these systems. Intentional anthropogenic disturbances can be used to manipulate forest composition and successional stage that directly encourage and support wildlife species that rely upon these systems. The impacts of these practices coupled with other seasonal disturbances on Neotropical migrant and resident bird communities and reproductive success are largely unknown regionally. This research sought to examine the natural response of the breeding bird community to a drought disturbance in a second-growth bottomland hardwood forest at Old Sabine Bottom Wildlife Management Area (OSBWMA), Smith County, Texas, in addition to providing a baseline assessment of habitat associations and reproductive success when the forest status is at desirable conditions. Bird community composition appeared fairly consistent between 2008 and 2014 with inhabitants including early and late-successional species, species with specialized habitat requirement, and species of conservation concern. As a result of the 2011 drought-induced disturbance, the OSBWMA experienced changes in stand structure including significant overstory mortality, increased number of snags and early-successional habitat. Densities of both Neotropical migrants and resident bird species were initially negatively impacted, in particular, canopy and cavity nesting species; however, within three years of this event, most species began to show signs of recovery and several early-successional species had either recovered completely, or exceeded, pre-drought density estimates. Overall, the drought-induced disturbance and resulting regeneration created vegetation heterogeneity within the forest (i.e., canopy gaps, understory stem density, vine cover, etc.) and were the main factors which structured and organized the breeding bird community at the OSBWMA. Although many species within the OSBMWA shared overlapping habitat associations, other species such as Acadian flycatchers (Empidonax virescens), prothonotary warblers (Protonotaria citrea) and Kentucky warblers (Geothlypis formosa), were correlated with a unique set of habitat characterisitics ultimately partitioning species into preferred habitats within the area. Mayfield nest success estimates were generally high for three early-successional focal species in this study, Northern cardinals (Cardinalis cardinalis; 43%), indigo buntings (Passerina cyanea; 38%), and white-eyed vireos (Vireo griseus; 38%). Forest structural changes following the drought, including gap creation and expansion and increased vine and shrub density, seemed to increase nesting success for Northern cardinals and indigo buntings but decreased nesting success for white-eyed vireos. In addition, overall parasitism and predation rates decreased after the disturbance for all three species providing evidence that post-drought OSBWMA contains suitable habitat for nesting early-successional species.