Michael L. Morrison’s research while affiliated with Texas A&M University and other places

Gaps in dispersal data limit habitat protection efforts. We sought to characterize such gaps and compare the utility of dispersal data from demographic and genetic methods in making habitat protection decisions. Here, we used a search string to retrieve dispersal studies for amphibians, reptiles, birds, and mammals. We included studies based on a set of selection criteria. We used this sample of selected studies to assess for persistence of taxonomic and geographic biases. We extracted non-effective (i.e., demographic) and effective (i.e., genetic) dispersal rates. We weighted these dispersal rates by associated sample size and standard deviation to indicate the ability to capture population-level dispersal. We then tested for variation in weighted dispersal by study type using Bayesian mixed-effects models. Amphibians were the most under-represented taxonomic group in our sample. Dispersal studies were mostly retrieved from developed nations indicating the distribution of dispersal research reflected GDP rather than the number of threatened species. The magnitude of dispersal from genetic methods exceeded demographic methods in all vertebrate groups considered in our study. Further, genetic studies consistently sampled a larger number of individuals. Thus, genetic methods may be better suited to characterize population-level dispersal. However, demographic and genetic approaches enable examination of the dispersal process at varying spatial and temporal scales and a combination of these approaches can be used to address persistent gaps in dispersal and enable land-management decisions.

Mitigating habitat loss of western burrowing owls (Athene cunicularia hypugaea) often involves relocation from California ground squirrel (Otospermophilus beecheyi) burrows to offsite nest boxes. Naval Air Station Lemoore (NASL), Kings and Fresno counties, California, initiated this approach to displace a regionally important population from airfield grasslands. We examined monitoring data of burrowing owls and fossorial mammals at NASL to assess mitigation options. Occupied nests increased by 33 (61%), with 47 nest box installations in 1997–2001, peaked at 87 in 1999, then declined by 50 through 2013. Although ≥13 nest boxes were occupied in 2000, none were occupied in 2003–2013. Within a 43.1 ha isolated grassland monitored for 13 years, nest site reuse in ground squirrel burrows averaged only 17% between any 2 consecutive years. Compared to the average density across grassland study areas, ground squirrel burrow systems/ha numbered 43% higher within 60 m of occupied nests and non-breeding-season burrows. Vegetation clearing to restore kangaroo rat (Dipodomys n. nitratoides) habitat preceded a 7.4-fold increase in ground squirrel burrow systems and a 4-fold increase in occupied nests, but drought-induced extirpation of ground squirrels eliminated occupied nests from the 43.1 ha grassland study area. Ground cover near occupied nests averaged 58% of the mean vegetation height and 67% of the mean percentage of bare ground in the field. Both nest sites and non-breeding-season burrows occurred >60 m interior to field edges 1.4 times more than expected. Non-breeding-season burrows averaged 328 m from same-year nest sites, and only 7% of non-breeding-season burrows were also used as nest sites. Mitigating habitat loss should be made more effective by fostering natural burrow construction by fossorial mammals on patches of short-stature vegetation that is sufficiently expansive to support breeding colonies of ≥12 pairs averaging ≥60 m from the field’s edge and a separation between non-breeding-season burrows and nest burrows minimally equal to mean nearest-neighbor distances among nests.

Townsend's big-eared bat, Corynorhinus townsendii, is a cave- and mine-roosting species found largely in western North American. Considered a species of conservation concern throughout much of its range, protection efforts would greatly benefit from understanding patterns of population structure, genetic diversity, and local adaptation. To facilitate such research, we present the first de novo genome assembly of C. townsendii as part of the California Conservation Genomics Project (CCGP). Pacific Biosciences HiFi long reads and Omni-C chromatin-proximity sequencing technology were used to produce a de novo genome assembly, consistent with the standard CCGP reference genome protocol. This assembly comprises 391 scaffolds spanning 2.1 Gb, represented by a scaffold N50 of 174.6 Mb, a contig N50 of 23.4 Mb, and a BUSCO completeness score of 96.6%. This high-quality genome will be a key tool for informed conservation and management of this vulnerable species in California and across its range.

Effective management decisions depend on knowledge of species distribution and habitat use. Maps generated from species distribution models are important in predicting previously unknown occurrences of protected species. However, if populations are seasonally dynamic or locally adapted, failing to consider population level differences could lead to erroneous determinations of occurrence probability and ineffective management. The study goal was to model the distribution of a species of special concern, Townsend's big‐eared bats (Corynorhinus townsendii), in California. We incorporate seasonal and spatial differences to estimate the distribution under current and future climate conditions. We built species distribution models using all records from statewide roost surveys and by subsetting data to seasonal colonies, representing different phenological stages, and to Environmental Protection Agency Level III Ecoregions to understand how environmental needs vary based on these factors. We projected species' distribution for 2061–2080 in response to low and high emissions scenarios and calculated the expected range shifts. The estimated distribution differed between the combined (full dataset) and phenologically explicit models, while ecoregion‐specific models were largely congruent with the combined model. Across the majority of models, precipitation was the most important variable predicting the presence of C. townsendii roosts. Under future climate scenarios, distribution of C. townsendii is expected to contract throughout the state, however suitable areas will expand within some ecoregions. Comparison of phenologically explicit models with combined models indicates the combined models better predict the extent of the known range of C. townsendii in California. However, life‐history‐explicit models aid in understanding of different environmental needs and distribution of their major phenological stages. Differences between ecoregion‐specific and statewide predictions of habitat contractions highlight the need to consider regional variation when forecasting species' responses to climate change. These models can aid in directing seasonally explicit surveys and predicting regions most vulnerable under future climate conditions. The goal of our study was to model the current distribution of Townsend's big‐eared bats (Corynorhinus townsendii) and estimate range shifts under future climate conditions at different temporal and geographic scales. We built species distribution models in present and future conditions using all records from statewide roost surveys and by subsetting this data to seasonal colonies and to Environmental Protection Agency Level III ecoregions. As a whole, the range of C. townsendii is expected to decrease throughout California, but within some ecoregions suitable areas will increase, highlighting the need to consider intraspecific variation when building species distribution models.

Distance sampling from aerial platforms can provide researchers with precise and efficient density estimates for wildlife populations, particularly over large areas. The intensity of the distance sampling survey depends on the survey effort. Effort can be referred to as coverage, where transect spacing is determined by the observer's sightability distance of the object or animal. Managers and researchers in Texas often use helicopters to survey and collect data for northern bobwhite (Colinus virginianus) density estimates. For bobwhites, 100% coverage represents transect spacing of 200 m, assuming observers can cover out to 100 m on either side of the transects. Often surveys are conducted at 50% coverage or 400 m spacing to reduce cost. Still, the implications of lowering survey effort on the precision of density estimates are unknown, particularly in coverage prescriptions. We flew 2,641 km of line transects each December from 2014 to 2017 and detected 2,333 bobwhite coveys across 7,648 ha of rangeland on the San Antonio Viejo Ranch in Jim Hogg County, TX, USA. We conducted line‐transect distance sampling from a helicopter platform at 50 and 100% coverage and simulated results at coverage <50% using empirical data. Based on the results of simulated surveys at <100% coverage, surveying for bobwhites using helicopters with less than 50% coverage results in variable density estimates (wide 95% confidence intervals) and low precision (coefficient of variation >20%). Empirical surveys conducted at 50 and 100% coverage show little variation in density estimates between the 2 levels of coverage. However, when broken into substrata (areas less than ~1,000 ha), conducting surveys at 50% coverage resulted in <60 detections, which led to low precision in density estimates (coefficient of variation >20%). Our results are based on surveys conducted at the juncture of the Coastal Sand Sheet and Tamaulipan Thorn Scrub ecoregions in south Texas and need to be evaluated in other arid and semi‐arid rangeland systems. Survey design is an essential component of estimating wildlife populations via distance sampling. However, the number of transects flown is often based on logistics rather than survey precision. We evaluated the variance associated with estimates from varying levels of survey coverage while using line‐transect distance sampling for northern bobwhites in Texas.

Bats are difficult to study due to their nocturnal, cryptic, and highly vagile nature. Ongoing advances in acoustic recording hardware and call classification software have made species detection and activity monitoring more feasible. Our objectives were to determine effort necessary to monitor bat assemblages using an occupancy framework and acoustic data, and to provide guidelines for researchers interested in developing similar monitoring programs. We collected data at two study areas in South Texas from June through September in 2015, 2016, and 2017. We used Pettersson D500X Mk II real-time full spectrum detectors and classified sound files using SonoBat bat call analysis software. We attempted to collect data during 2 visits to individual sites with up to 5 consecutive nights per visit each year. We estimated occupancy rates for each species in each study area using occupancy models in Program MARK and included terms to define trends in detection probability through the season. Over the 3 years of our study, we sampled 106 sites with 803 sampling nights and classified a total of 2880 sound files to 7 species. Datasets for 6 of the species supported models indicating detection probability varied throughout our sampling period. Our results generally indicate that sample sizes between 10 and 20 sites would be required to detect declines in occupancy of 50% over 25 years using 10 nights per site with a starting occupancy rate of 0.70. Detecting declines of 30% in 10 years may require > 75 sampling sites. Finally, our analysis shows that recognizing seasonal variation in detection probability, and then timing surveys accordingly, can greatly reduce sample size requirements.

White-nose syndrome (WNS) is caused by the fungus Pseudogymnoascus destructans and has led to the deaths of millions of North American bats since it was first documented in New York in 2006. Since the first cases were recorded, WNS has spread rapidly across North America and is now confirmed or suspected in 40 US states and seven Canadian provinces. Often, the presence of P. destructans is detected in a cave or hibernaculum before signs of WNS manifest in the resident bat population, making presence of the fungus a more reliable assessment of potential epidemic spread than expansion of manifested WNS. An analysis of 43 cave internal climates across the state of Texas revealed a pattern of thermal suitability for P. destructans that correlated significantly with landscape (elevation, lithology) and external climate (mean surface temperature and precipitation). We generated a predictive model to assess the potential spread of P. destructans through Texas karst systems based on external features that correlate with suitable internal climates for fungal growth. Applications of this model to external climatic variables from 2019 showed seasonally varying patterns of suitability for fungal growth in select regions of Texas karst systems. Results from these surveys and models showed that internal climates of Texas caves are likely able to sustain the growth of P. destructans and could cause disease and resulting declines in Texas bats, and act as stepping-stones for the fungus, allowing it to travel southward into Mexican and Central American cave systems. The resulting work will inform researchers and natural resource managers of areas of significant concern to monitor for the spread of WNS.

Cases of albinism have been reported in less than 2% of living rodent species. Here, we report the first description of complete albinism in Baiomys taylori along with photographic evidence. This adult female was captured on three occasions as part of a long-term small mammal study on rangelands of extreme southern Texas. The individual was developing teats upon the third capture, an early sign of pregnancy. Despite selective pressures against albino phenotypes, this animal was able to survive to adulthood and potentially pass its albino alleles to offspring.