Geology topics

Research about Aransas National Wildlife Refuge

Source-linked reports with geographic coverage including Aransas National Wildlife Refuge.

6 recordsLinked to original sources

USGS2026

Inland habitat selection model for wintering whooping cranes

Inland habitat use by wintering Aransas-Wood Buffalo whooping cranes ( Grus americana ) is expected to increase given projected population growth and observations of some whooping cranes using inland winter habitat in addition to coastal marshes. We developed resource utilization functions using ‘random forests’ to model whooping crane use as a function of environmental covariates considered important for whooping crane use. Covariates associated with distance to cropland, distance to development, and wetness or standing water were the most influential in model prediction. The model estimated that the 50% predicted use contour encompassed 34,925 hectares (ha) and the 95% predicted use contour encompassed 328,928 ha within the study area. While presently limited by the small sample size of inland wintering areas observations ( n = 7 cranes with ≥50 locations), this model provides an initial tool for identifying potential impacts to whooping crane inland habitat use in proximity to anthropogenic development. The model can be expanded to incorporate future data to reduce uncertainty.

Texas↗

USGS2025

Mortality of fledged whooping cranes in the Aransas-Wood Buffalo Population

Maintaining accurate mortality records for endangered species is important for guiding management and conservation actions. Mortalities of whooping cranes ( Grus americana ) in the Aransas-Wood Buffalo Population (AWBP) are documented in published records from 1950 through 2010. This paper documents publicly available records of known mortalities from 2011 through 2023, and updates historic records from 1950 to 2010. Public sightings and telemetry carcass records were restricted to fledged whooping cranes from the AWBP and stratified by confirmed, suspected, and unknown causes across the annual range (i.e., summer, migration, and winter). This mortality update provides more certainty associated with available carcass data and reduces discrepancies in existing published information.

Texas↗

USGS2022

Space use and site fidelity of wintering whooping cranes on the Texas Gulf Coast

The Aransas-Wood Buffalo population (the only non-reintroduced, migratory population) of endangered whooping cranes ( Grus americana ) overwinters along the Texas Gulf Coast, USA. Understanding whooping crane space use on the wintering grounds reveals essential aspects of this species' ecology, which subsequently assists with conservation. Using global positioning system telemetry data from marked whooping cranes during 2009–2017, we fit continuous-time stochastic process models to describe movement and home range using autocorrelated kernel density estimation (AKDE) and explored variation in home range size in relation to age, sex, reproductive status, and drought conditions. We used the Bhattacharyya coefficient of overlap and distance between home range centroids to quantify site fidelity. We examined the effects of time between winter home ranges and the sex of the crane on site fidelity using Bayesian mixed-effects beta regression. Winter whooping crane 95% AKDE home range size averaged 30.1 ± 45.2 (SD) km 2 (median = 14.3, range = 1.1–308.6). Home ranges of sub-adult females were approximately 2 times larger than those of sub-adult males or families. As drought worsened, home ranges typically expanded. Between consecutive years, the home ranges of an adult crane exhibited 68 ± 31% overlap (site fidelity), but fidelity to winter sites declined in subsequent winters. The overlap of adult home ranges with the nearest unrelated family averaged 33 ± 28%. As a whooping crane aged, overlap with its winter home range as a juvenile declined, regardless of sex. By 4 years of age, a whooping crane had approximately 14 ± 28% overlap with its juvenile winter home range. Limited evidence suggested male whooping cranes return to within 2 km of their juvenile home range by their fifth winter. Previous data obtained from aerial surveys led ecologists to assume that whooping crane families normally used small areas (~2 km 2 ) and expressed persistent site fidelity. Our analyses showed <8% of families had home ranges ≤2 km 2 , with the average area 15 times greater, and waning site fidelity over time. Our work represents an analysis of whooping crane home ranges for this population, identifying past misconceptions of winter space use and resulting in better estimates of space requirements for future conservation efforts.

Texas↗

USGS2013

The relationship of blue crab abundance to winter mortality of Whooping Cranes

We sampled blue crab (Callinectes sapidus) numbers in marshes on the Aransas National Wildlife Refuge, Texas from 1998-2006, while simultaneously censusing the wintering population of Whooping Cranes (Grus americana) on the refuge and surrounding habitats. This was done to determine whether mortality of wintering Whooping Cranes was related to the availability of this food source. Yearly variation in crab numbers was high, ranging from a low of 0.1 crabs to a high of 3.4 crabs per 100-m transect section. Significant non-linear increases in both juvenile and adult mortality in relation to decreasing crab abundance was observed. Results suggest that some threshold of crab abundance exists in which Whooping Cranes have higher survival on their wintering grounds.

Texas↗

USGS2008

A low intensity sampling method for assessing blue crab abundance at Aransas National Wildlife Refuge and preliminary results on the relationship of blue crab abundance to whooping crane winter mortality

We sampled blue crabs ( Callinectes sapidus ) in marshes on the Aransas National Wildlife Refuge, Texas from 1997 to 2005 to determine whether whooping crane ( Grus americana ) mortality was related to the availability of this food source. For four years, 1997 - 2001, we sampled monthly from the fall through the spring. From these data, we developed a reduced sampling effort method that adequately characterized crab abundance and reduced the potential for disturbance to the cranes. Four additional years of data were collected with the reduced sampling effort methods. Yearly variation in crab numbers was high, ranging from a low of 0.1 crabs to a high of 3.4 crabs per 100-m transect section. Mortality among adult cranes was inversely related to crab abundance. We found no relationship between crab abundance and mortality among juvenile cranes, possibly as a result of a smaller population size of juveniles compared to adults.

Texas↗

USGS1982

Chlamydiosis in 2 biologists investigating disease occurrences in wild waterfowl

Chlamydiosis (ornithosis, psittacosis) is an infectious disease of birds that can be transmitted to humans. Human infections are probably acquired by inhalation of aerosols containing elementary bodies of the causative agent Chlamydia psittaci , from bird droppings, or from tissues. Infected birds do not have to be ill to transmit the organism (Schachter and Dawson 1978). The disease in humans is considered an occupational risk for people working with pet birds (particularly psittacine species) and poultry, but all avian species can be considered as potential reservoirs (Schachter and Dawson 1978). Burkhart and Page (1971) listed >130 species of wild birds as being infected. The purpose of this report is to draw the disease to the attention of those working with wild birds by describing 2 cases acquired from wild waterfowl and by reviewing other information on human infections associated with wild birds. We do this because the disease can be serious if not treated properly, and because the disease is not usually associated with wild birds the diagnosis may not be considered by physicians without some prompting from the patient.

California, Manitoba, Saskatchewan, Texas, Wiscons↗