Current and Past Research
My research interests are broadly focused on the ecology and conservation of birds and mammals. While I have conducted research on a variety of mammals including collared peccary, kangaroo rats, and bats, the majority of my research since arriving at Texas State has focused on birds, and more specifically waterbirds.
Broadly, I am interested in both ecological and evolutionary studies of birds but likewise interested in applied research on birds, specifically the conservation and management of bird populations.
Areas of specific research interest include 1) ecology and conservation of Reddish Egrets (Egretta rufescens), 2) ecology and conservation of Black Rails (Laterallus jamaicensis), 3) methodologies of surveying colonial waterbirds and secretive marshbirds, 4) the use of wildlife crossings (bridges, culverts) by various mammalian species and, 5) the ecology and conservation of other waterbirds including Green Herons (Butorides virescens). Below is more about some of these specific topics:
Ecology and Conservation of Reddish Egrets
I have been studying Reddish Egrets for over 18 years and been actively involved in the Reddish Egret Working Group since its founding in 2005. Recent research on Reddish Egrets has included movement ecology of adult and juvenile Reddish Egrets through color banding and satellite telemetry, conservation genetics across the range of the species and general nesting and foraging ecology of the species. For more information about Reddish Egrets, please visit our working group website Reddish Egrets
Ecology and Conservation of Black Rails
The Black Rail (Laterallus jamaicensis) is a candidate species to be listed as “threatened” under the U.S. Endangered Species Act that inhabits emergent salt marsh of the Texas Gulf Coast. Black Rails are also listed as species of high priority by the Texas Wildlife Action Plan. At the regional and continental level, the species is a priority species for the Gulf Coast Joint Venture and listed as high concern and ranks as the most threatened marsh bird in North America (priority marsh bird species listed by Waterbird Conservation for the Americas). Partly due to its secretive behavior and habitat affinity within dense and often inaccessible marshes, the species has been poorly studied and many aspects of its ecology, life history and behavior are unknown. Along the Texas Gulf Coast, the population has never been rigorously surveyed; therefore occupancy rates and overall abundance are lacking for the Texas population.
We conducted point count surveys and collected habitat measurements at survey points along the Texas coast to estimate occupancy rates by habitat during the breeding season. We explored various spatial predictors of Black Rail occupancy and developed and tested a survey protocol. This project provided baseline data for estimates of detectability, occupancy and abundance of Black Rails in Texas. More recently, we have explored home range of nesting Black Rails, winter use by Yellow and Black Rails, and variation in acoustic calling of Black Rails along the Texas Gulf Coast.
Methodologies of surveying and detecting colonial nesting and secretive nesting waterbirds
We have been exploring the use of unmanned aerial vehicles (UAVs) to survey waterbird colonies and use UAVs to track colony phenology and assess species diversity using the colonies for nesting. While conducting these studies, we have also assessed the possible disturbance effects of UAV on nesting waterbirds. We will also be comparing UAV survey counts with standardized ground counts conducted on waterbird colonies in Texas.
Influence and ecological significance of plumage coloration in waterbirds
My doctoral research on plumage coloration in herons investigated the ecological significance of plumage coloration in relation to sociality and foraging behavior. White plumage has apparently evolved independently on numerous occasions in the order Ciconiiforms (herons, ibises and their allies). Closely related species of herons differ considerably in plumage coloration with one species being dark plumage (e.g. little blue heron Egretta caerulea) and one species being all-white (e.g. snowy egret E. thula). I tested several hypotheses related to the influence of white plumage including crypsis to prey, foraging tactics and flock formation and utilization. White plumage has long been hypothesized to facilitate social foraging in herons by attracting birds to a given area. The apparent costs of attracting potential competitors to a given area may be offset by minimizing the risk of predation and/or increase foraging efficiency. Through a series of experimental manipulations with heron decoys, I found white plumage did not serve as a universal attractant to herons and instead species were attracted to like-plumaged and like-size decoys (Green and Leberg 2005). I also investigated inter-individual spacing of foraging white and dark-plumaged wading birds; hypothesizing that if white plumage increases sociality in wading birds, we would expect to find white birds closer in spacing to one another and conversely, dark-plumaged species would be more solitary. In a series of paired observations, we found that white-plumaged species were not closer together than that based on random chance and for snowy egrets specifically, they were significantly further apart than that based on random chance (Green and Leberg 2006). White plumage may confer a foraging advantage in open (unvegetated) water habitat as fish appear to detect the presence of dark plumaged birds (Green and Leberg 2005). However, there was no evidence for this presumed advantage in behavioral comparisons between white and dark plumaged species of herons. Within the plumage dimorphic reddish egret (Egretta rufescens), this presumed advantage was evident in behavioral comparisons between white and dark morphs using specific foraging tactics (Green 2005). In continuation of my research on the plumage dimorphic Reddish Egret, I have several students examining aspects of this species ecology including potential genetic differentiation, nesting behavior, dispersal behavior and juvenile survival between color morphs.