Ashley M. Long

Using LiDAR-derived vegetation metrics for high-resolution, species distribution models for conservation planning

Advances in remotely sensed data for characterizing habitat have enabled development of spatially explicit predictive species distribution models (SDM) that can be essential tools for management. SDMs commonly use coarse-grain metrics, such as forest patch size or patch connectivity, over broad spatial extents. However, species distributions are likely driven in part by local, fine-grained habitat conditions. Conservation and management are often planned and applied locally, where coarse predictions may be uninformative or not sufficiently precise. We investigated the integration of high-resolution LiDAR (Light Detection and Ranging) with avian point sampling data to develop a detection-corrected occupancy model to quantify habitat-occurrence relationships for two species with different habitats: the endangered golden-cheeked warbler (Setophaga chrysoparia) and black-capped vireo (Vireo atricapilla) on a military installation in central Texas. We compared occupancy models that used only the more conventional, coarse remotely sensed metrics to models that also incorporated high-resolution LiDAR-derived metrics for vegetation height and canopy cover, to assess their use for predicting distributions. Models including LiDAR-derived vegetation height and canopy cover metrics were competitive for both species, and models without LiDAR-derived vegetation height had substantially lower model weights and explanatory strength. Area under curve estimates for the highest ranked models were high for warblers (0.864) and moderate for vireos (0.746). Using the best supported models for each species, we predicted the occurrence distribution for both species. The resulting predictions provide a decision support tool that enables assessment of the status, impacts, and mitigation of impacts to endangered species habitat on the installation due to land management and military training activities that is more standardized and accurate than current assessment approaches based on visual gestalt of habitat and expert opinion. Additionally, although previous species distribution models have been created for our focal species, most fail to match the grain and extent of most management actions or include local, fine-grained metrics that influence distributions. In contrast, we demonstrate that use of LiDAR with species occurrence data can provide precision and resolution at a scale that is relevant ecologically and to the operational scale of most conservation and management actions.

Modeling Spatially Explicit Densities of Endangered Avian Species in a Heterogeneous Landscape

ABSTRACT. Relating population density to spatially explicit habitat characteristics can inform management by directing efforts to areas with lower densities or focusing conservation and land protection on high-density areas. We conducted point-transect surveys for the endangered Golden-cheeked Warbler (Setophaga chrysoparia) and Black-capped Vireo (Vireo atricapilla) in the live-fire region of Fort Hood, Texas. We used mark—recapture distance sampling and combined a Horvitz-Thompson estimator with a habitat-based, resourceselection gradient to estimate spatially explicit density for both species. We detected Golden-cheeked Warblers at 120 locations (202, 197, and 89 detected by primary, secondary, and both observers, respectively) and Black-capped Vireos at 173 locations (241, 255, and 107 detected by primary, secondary, and both observers, respectively). For Golden-cheeked Warblers, the average (± SE) composite detection probability estimate within a 100-m point-sample radius was 0.57 ± 0.14, and for vireos it was 0.24 ± 0.02. Estimated mean density (singing males ha-1) was 0.14 ± 0.03 (95% confidence interval [CI]: 0.08–0.23) and 0.47 ± 0.05 (95% CI: 0.38–0.60) for Golden-cheeked Warblers and Black-capped Vireos, respectively. Our analysis suggested evidence of heterogeneity in the detection process for both species, as well as imperfect detection at distance g(0), both of which would bias estimated densities if ignored. Additionally, both species exhibited spatial variability in estimated densities, with those areas that had higher occurrence probabilities typically having higher estimated density. In the absence of spatially explicit density prediction, managers must treat all losses of potential habitat for endangered species uniformly, despite likely differences in conservation value. Our approach could be used to ascertain areas of changing density in relation to changing habitat conditions over time and space.

ORIENTATION OF GRASSHOPPER SPARROW AND EASTERN MEADOWLARK NESTS IN RELATION TO WIND DIRECTION

Abstract. Orientation of the entrances of bird nests may be especially important in grasslands, where protective cover from solar radiation and wind is minimal. We examined orientation patterns of nest-dome entrances in two grassland bird species, the Grasshopper Sparrow (Ammodramus savannarum) and the Eastern Meadowlark (Sturnella magna). We noted how these patterns changed over the nesting season and how they related to prevailing wind direction. We found that Grasshopper Sparrow (n = 333) and Eastern Meadowlark (n = 272) nests were oriented nonrandomly, toward the northeast (ā = 33.4° and 52.9°, respectively). Prevailing wind in the study region was approximately from the south (ā = 171.1°); therefore, nests of the two species were generally oriented downwind. Nest orientation of the Eastern Meadowlark shifted northward as the nesting season progressed, coinciding with a southeastward shift in prevailing wind direction. Conversely, in one year we observed a seasonal shift toward the east in nest orientation of the Grasshopper Sparrow. Nest orientation in these species may represent a trade-off between various factors, including wind and solar radiation.

Orientation of Sap Wells Excavated by Yellow-bellied Sapsuckers

Abstract Ambient temperature may influence selection of foraging sites by organisms that use sap as a primary food source. I examined the spatial orientation of sap wells excavated by Yellow-bellied Sapsuckers (Sphyrapicus varius) on pine trees (Pinus spp.; n  =  43) in eastern Kansas. Sap wells were oriented toward the southwest (ā  =  246.04°, s  =  65.46°, P  =  0.004), unlike in previous studies. Benefits of southwesterly sap well orientation may include avoidance of high winds while foraging and increased flow of sap on the sides of trees warmed by afternoon light.

A before–after control–impact assessment to understand the potential impacts of highway construction noise and activity on an endangered songbird

Abstract Anthropogenic noise associated with highway construction and operation can have individual‐ and population‐level consequences for wildlife (e.g., reduced densities, decreased reproductive success, behavioral changes). We used a before–after control–impact study design to examine the potential impacts of highway construction and traffic noise on endangered golden‐cheeked warblers (Setophaga chrysoparia; hereafter warbler) in urban Texas. We mapped and monitored warbler territories before (2009–2011), during (2012–2013), and after (2014) highway construction at three study sites: a treatment site exposed to highway construction and traffic noise, a control site exposed only to traffic noise, and a second control site exposed to neither highway construction or traffic noise. We measured noise levels at varying distances from the highway at sites exposed to construction and traffic noise. We examined how highway construction and traffic noise influenced warbler territory density, territory placement, productivity, and song characteristics. In addition, we conducted a playback experiment within study sites to evaluate acute behavioral responses to highway construction noises. Noise decreased with increasing distance from the highways. However, noise did not differ between the construction and traffic noise sites or across time. Warbler territory density increased over time at all study sites, and we found no differences in warbler territory placement, productivity, behavior, or song characteristics that we can attribute to highway construction or traffic noise. As such, we found no evidence to suggest that highway construction or traffic noise had a negative effect on warblers during our study. Because human population growth will require recurring improvements to transportation infrastructure, understanding wildlife responses to anthropogenic noise associated with the construction and operation of roads is essential for effective management and recovery of prioritized species.

INFLUENCE OF PRESCRIBED BURNING ON BIRD ABUNDANCE AND SPECIES ASSEMBLAGE IN A SEMIARID GREAT PLAINS GRASSLAND

Abstract. Encroachment of woody plants is widespread in semiarid grasslands of the southwestern United States. Wildlife responses to shrub removal techniques in the region are relatively unknown. In 2008 and 2009, we examined avian responses to prescribed burning of ungrazed shortgrass prairie within a study area (4811 ha) near Amarillo, Texas, that is heavily encroached by honey mesquite (Prosopis glandulosa) and cholla (Opuntia spp.). Specifically, we compared relative abundance, species richness, and species diversity of breeding birds across large, spatially replicated experimental plots burned every 2 or 4 years since 2002 and unburned controls. We found no significant differences in the mean relative abundance of most species across the treatments. However, Northern Bobwhite (Colinus virginianus), Cassins Sparrow (Peucaea cassinii), and Brown-headed Cowbird (Molothrus ater) were more abundant in less frequently burned plots and unburned controls. We found no differences in species richness or diversity across the treatments. Limited variation in avian responses across the treatments likely reflects the uniform pattern of vegetation structure we found across the plots, despite repeated application of prescribed fire at 2- and 4-year intervals over a 7-year period. Differences in bird species assemblages among the burn treatments might be more prominent in future years as prescribed burning continues.

Nest defense behavior of Greater Roadrunners (Geococcyx californianus) in south Texas

ABSTRACT The Greater Roadrunner (Geococcyx californianus) is a medium-sized predatory bird that occurs widely across the southwestern United States. Despite its prevalence in this region, studies examining the nesting and behavioral ecology of this species are limited. In 2015 and 2016, we examined relatively unknown aspects of roadrunner natural history by using infrared video cameras to observe antipredator behaviors associated with Greater Roadrunner nest defense. Nest predation accounted for all nesting failures in our study. The Great Plains rat snake (Pantherophis emoryi) accounted for 70.0% of nest predation. We observed rat snakes entering the nest and consuming eggs or nestlings for >6 min before roadrunners flushed from nest sites. We also observed 53.3% of roadrunners actively defending nest sites from snake predators and zero defending nests from coyotes (Canis latrans), likely because of the predator size. Active defense sessions in our study lasted 1 min 20 s (95% CI 1 min 17 s) and consisted of 12.0 (95% CI 3.4) bill strikes per min of active defense. We observed no successful nest defenses because partial nest contents were lost during each event; however, >50% of predation events with an active defense session resulted in preservation of at least one viable egg or chick, indicating nest defense was a valuable behavior. Examining nest defense behaviors in larger, predatory birds may elucidate risks and rewards associated with nest defense that may not be observed in studies focusing primarily on passerines.

Does Age Structure Influence Golden-Cheeked Warbler Responses Across Areas of High and Low Density?

Abstract. Age-based differentiation in the timing of avian migration can influence subsequent habitat use and, therefore, reproductive success. Over 2 breeding seasons, we compared arrival dates, pairing success, and fledging success for second-year (SY) and after-second-year (ASY) federally endangered Golden-cheeked Warblers (Setophaga chrysoparia) occupying areas of low (n = 9 sites) and high (n = 10 sites) warbler density. Male warblers arrived on low-density sites on average 6 days later (11 March) than high-density sites (5 March). Male warblers that established territories on low-density sites tended to be younger than male warblers that established territories on high-density sites. Overall pairing and fledging success were similar across low- and high-density sites, but overall pairing and fledging success were lower for SY males compared to ASY males; no SY birds fledged young on low-density sites. We found no difference in pairing or fledging success for ASY males at low- and high-density sites. For some species, habitat that supports fewer birds may be of lower quality. However, warblers in our study area fledged young at low- and high-density sites. As such, low-density sites may fill an important role in conservation efforts for this species.

Responses of an Endangered Songbird to an Extreme Drought Event

Abstract Given natural variation in weather conditions and increased risk of drought associated with climate change, understanding how birds respond to fluctuations in precipitation is a necessary step toward development of more-effective, long-term management strategies for species of conservation concern. We compared behaviors and reproductive output of the federally endangered Vireo atricapilla (Black-capped Vireo, hereafter Vireo) during an extreme drought event and a year with moderate rainfall. During the drought, Vireos had lower pairing and territory success, delayed nest initiation, fewer re-nesting attempts, and lower nest-success. Brood parasitism by Molothrus ater (Brown-headed Cowbirds), which is one of the main threats to Vireo population persistence, was also greater during the drought year. Nest placement varied between years, with Vireos using the evergreen Juniperus asheii (Ashe Juniper) as a nest substrate more often when conditions were dry and the deciduous Diospyros texana (Texas Persimmon) under moderate conditions. Removal of Ashe Juniper and Brown-headed Cowbirds from Vireo habitat are common management practices used to support Vireo conservation efforts. Our results suggest that regional weather patterns should be considered when making decisions regarding Ashe Juniper removal. In addition, increased Brown-headed Cowbird removal may be warranted in dry areas during drought years.

Responses of a Federally Endangered Songbird to Understory Thinning in Oak-Juniper Woodlands

Wildlife conservation and management on military lands must be accomplished in the context of military readiness, which often includes ground-based training that is perceived to conflict with wildlife needs and environmental regulations. From 2008‒2012, we examined territory density, pairing success, and fledging success of the federally endangered golden-cheeked warbler (Setophaga chrysoparia; hereafter warbler) in relation to removal of small-diameter trees from the understory of mature oak-juniper (Quercus-Juniperus) woodland at the 87,890 ha Fort Hood Military Reservation in central Texas. Understory thinning created troop maneuver lanes, but left canopy vegetation intact. Warbler density, pairing success, and fledging success were similar across thinned and control sites. We found that warbler pairing and fledging success were best predicted by Ecological site (hereafter Ecosite), an indicator of hardwood tree species composition. Warbler pairing and fledging success were about 1.5 and 1.6 times higher, respectively, for territories dominated by the Low Stony Hill Ecosite than territories dominated by the Redlands Ecosite. Our results indicate that understory thinning for military training purposes did not have a negative effect on warblers at Fort Hood in the manner tested, and suggest that removal of smaller trees from the understory in a way that replicates historic conditions may elicit neutral responses from this forest-dependent songbird. Quantifying wildlife responses to military activities provides the Department of Defense and US Fish and Wildlife Service with data to guide conservation of threatened and endangered species on Department of Defense facilities while maintaining the military mission, and supports wildlife management efforts on other public and private lands.