Laguna Atascosa National Wildlife Refuge Research Articles

Using Bayesian multispecies models to evaluate fish and invertebrate detection probability and distribution in the hypersaline Bahia Grande tidal basin

AbstractObjectiveIn 2000, the Laguna Atascosa National Wildlife Refuge acquired the Bahia Grande (Texas) management unit, a space that had lain barren and arid for 70 years. A large cooperative partnership launched a restoration project to replenish the basin and recover its original tidal hydrology. In 2005, the construction of a pilot channel successfully restored water throughout the basin, and plans to eventually widen the channel were developed. Our study aims to evaluate an estuarine habitat restoration by assessing ecological drivers and the impacts on species diversity.MethodsWe evaluated species richness, detection/occupancy rates, and species–habitat relationships, and we estimated the sampling effort required to achieve a given level of relative precision if relative abundance was used instead of occupancy to inform future sampling. Sampling gear included bag seines for juvenile life stages and gill nets for capturing subadult and adult life stages. For analysis, we used a Bayesian negative binomial linear mixed‐effects model to evaluate richness–habitat relationships and a hierarchical Bayesian multispecies model to evaluate individual species–habitat relationships, and we calculated the total number of fish captured and relative standard error by gear and sample year to produce a precise estimate of relative abundance.ResultOverall, 29 species were caught between 2018 and 2021. Salinity emerged as a clear driver in the Bahia Grande, as both species richness and individual‐level responses were negatively associated with high salinity values. We found that catch estimated as relative abundance had much variability, as is typical of most survey programs assuming constant detectability, and the number of net sets or seine hauls required to achieve a given level of relative precision varied considerably depending on the species, season, year, and gear type. The most collected species were found in the upper extremes of their salinity tolerances—potentially a unique adaptation to this hypersaline system.ConclusionBaseline data suggest that for the channel widening to be successful, there must be a noticeable increase in suitable habitat characteristics throughout the basin.

Trypanosoma cruzi and Incidental Sarcocystis spp. in Endangered Ocelots (Leopardus pardalis) of South Texas, USA.

The federally endangered ocelot (Leopardus pardalis) population of south Texas, USA is declining; fewer than an estimated 80 ocelots remain. South Texas has robust transmission of Trypanosoma cruzi, the protozoan parasite causing Chagas disease in humans and various mammals. This parasite's impact in ocelots is unknown. Blood from live-trapped ocelots was collected by US Fish and Wildlife Service personnel in an annual monitoring program; additionally, tissues were obtained from carcasses collected from 2010 to 2017 around Laguna Atascosa National Wildlife Refuge in south Texas and placed in scientific collections. Variable samples were available from 21 ocelots: skeletal muscle (n=15), heart tissue (n=5), lung (n=1), kidney (n=1), spleen (n=1), liver (n=1), blood clot (n=9), and serum (n=3). Overall, 3/21 (14.3%) ocelots showed evidence of T. cruzi infection or exposure, with T. cruzi PCR-positive samples of skeletal muscle, heart, and blood clot, respectively. All three were infected with the T. cruzi discrete taxonomic unit "TcI"; one of these ocelots also had anti-T. cruzi antibodies. Lymphoplasmacytic inflammation was noted in the PCR-positive heart tissue and in some PCR-negative tissues from this and other individuals. Incidentally, Sarcocystis spp. were noted histologically in five ocelots. Trypanosoma cruzi infection and associated cardiac lesions suggest that this parasite should be further investigated in vulnerable populations.

Evaluating population connectivity and targeting conservation action for an endangered cat

AbstractDispersal of animals among populations helps to increase genetic variability and population viability. The endangered ocelot (Leopardus pardalis) in south Texas persists in two small populations separated by 30 km and cutoff from populations in northeastern Mexico. Despite the relatively short distance separating the two south Texas populations, movement between them has been limited, leading researchers to believe landscape connectivity is poor in the region. We developed habitat suitability maps using remote sensing and GPS‐collared ocelots and ran connectivity analyses to assess current habitat linkages, important areas for conservation, and areas where connectivity could be improved through habitat restoration. First, we developed a resource selection function using random forest models and GPS data from ten ocelots collared at Laguna Atascosa National Wildlife Refuge combined with spatial layers derived from LiDAR and remotely sensed imagery. We then used these results as the basis for a cost surface layer. Using this layer, we examined habitat connectivity using least‐cost and circuit theory methods. We evaluated linkages by cost of movement, identified areas important for maintaining existing connectivity, and ranked areas where restoration would have the greatest benefit to connectivity. We found that core habitats within the two populations were relatively well connected but connectivity between the two populations was poor. By identifying areas currently important for connectivity and areas with the greatest benefit to ocelots if restored, these results will help inform land acquisition and restoration planning to improve ocelot conservation in south Texas.

Molecular screening for rickettsial bacteria and piroplasms in ixodid ticks surveyed from white-tailed deer (Odocoileus virginianus) and nilgai antelope (Boselaphus tragocamelus) in southern Texas.

A survey of ixodid ticks parasitizing white-tailed deer (Odocoileus virginianus) and nilgai antelope (Boselaphus tragocamelus) was completed during the 2018–2019 public hunt season on the Laguna Atascosa National Wildlife Refuge (Cameron County, Texas) and the East Foundation's El Sauz Ranch in nearby Willacy County (Texas). Anocenter nitens was the predominant tick species identified with 5% of these ticks collected from nilgai. All life stages were encountered in high numbers on white-tailed deer, indicating that deer may be a primary host in this region. Amblyomma maculatum and Amblyomma inornatum were identified from both hosts, while Ixodes scapularis was encountered only on white-tailed deer. This is the first published record of A. inornatum on nilgai. A subset of ticks was used in PCR assays to detect Rickettsia spp., family Anaplasmataceae, Borrelia spp., and Theileria-Babesia spp. Borrelia spp. were not detected in any of the ticks analyzed. Rickettsia parkeri was detected in three A. maculatum adult ticks from deer, Rickettsia sp. endosymbiont sequences were present in all I. scapularis ticks, and Rickettsia amblyommatis was detected in three A. inornatum adult ticks from deer. Sequence analysis of Anaplasmataceae-positive amplicons from A. nitens and A. maculatum had low percent identity to published Anaplasma spp. sequences, suggesting a unique Anaplasma sp. may be circulating in the population. Anaplasma platys was detected from A. nitens larvae and an Ehrlichia sp. Delta strain was present in A. maculatum, both of unknown pathogenicity towards deer. Theileria cervi was detected in all stages of A. nitens ticks, and positive ticks originated from 27 of 31 deer and a single nilgai sampled from throughout the survey site. The primary vector for T. cervi is absent from this region, suggesting T. cervi is possibly maintained by a different tick species.

Persistent organic pollutants in eggs from south Texas Aplomado falcons.

A program to reintroduce the Northern Aplomado falcon (Falco femoralis septentrionalis) in south Texas and the southwestern United States was initiated in the late 1970s. Fledgling Aplomado falcons were first released in the Laguna Atascosa National Wildlife Refuge in 1993 and the first nesting pair in the area was recorded by 1995. During 2004-2017 we collected addled eggs from nesting pairs in the Laguna Atascosa National Wildlife Refuge and Matagorda Island in south Texas, to determine if environmental contaminants in Aplomado falcon eggs had decreased over time and if eggshell thickness values were similar to those in the pre-DDT era. We analyzed organochlorine pesticides, PCBs, and PBDEs in 60 egg homogenates by gas chromatography-mass spectrometry. Eggshells were measured to determine thickness and to correlate with contaminant concentrations. Mean concentration in eggs were 244ng/g ww for p,p'- DDE, 270ng/g ww for PCBs and 10ng/g ww for PBDEs. These values were lower than those reported in a previous study for eggs collected between 1999 and 2003, with a mean of 821ng/g ww for p,p'-DDE and 1228ng/g ww for total PCBs. Eggshell thickness ranged from 0.206mm to 0.320mm (n=156). Overall, contaminant concentrations in eggs of Aplomado falcons were low, at levels not likely to impact the recovery of the species. Data from this and previous studies indicate that DDE has decreased significantly in eggs of Aplomado falcons over the last 25 years in south Texas. Breeding populations have been steady at over 30 breeding pairs in south Texas since 2011, although they decreased to 24 pairs in 2018 following Hurricane Harvey.

Coastal Prairie Recovery in Response to Shrub Removal Method and Degree of Shrub Encroachment

Shrub encroachment into grasslands is a worldwide phenomenon with no signs of abating and numerous ecological consequences. In South Texas, honey mesquite (Prosopis glandulosa Torr.) and huisache (Vachellia farnesiana [L.] Wight & Arn.) are two shrubs encroaching into coastal prairies, reducing cover of the dominant native grass, gulf cordgrass (Spartina spartinae [Trin.] Merr. ex Hitchc.), and decreasing habitat for the endangered Aplomado Falcon (Falco femoralis), which requires grasslands or savannas for survival. To determine the best management approach for deterring shrub encroachment and restoring native grasslands, the US Fish and Wildlife Service used several shrub removal techniques within coastal prairies of the Bahía Grande Wetland Complex of the Laguna Atascosa National Wildlife Refuge, a core site for Aplomado Falcon reintroductions. Here, we assess native grass recovery over a 2-yr period in response to these shrub removal methods (mechanical plus prescribed fire and/or herbicide treatments) and degree of shrub encroachment before treatment. In general, areas with high levels of shrub encroachment before treatment had the highest amount of bare ground and lowest grass cover immediately following an initial mechanical treatment; this legacy effect persisted throughout the study irrespective of shrub removal treatment. Regardless of degree of shrub encroachment before treatment, grasses in areas treated with either mechanical or mechanical followed by herbicide methods recovered the slowest, likely due to residual woody material that hindered seed germination. Herbicide treatment following mechanical removal or mechanical removal plus fire effectively hindered shrub regrowth. Overall, mechanical treatment followed by prescribed fire and then herbicide application most effectively promoted grass recovery while hindering shrub regrowth. These findings suggest that grassland recovery following shrub encroachment into South Texas coastal prairies may be promoted through the application of shrub removal methods that combine mechanical, fire, and herbicide treatments.

Population density and habitat associations of the Seaside Sparrow (Ammodramus maritimus) on Laguna Atascosa National Wildlife Refuge, Cameron County, Texas

ABSTRACT In 2000, a resident population of Texas Seaside Sparrows (Ammodramus maritimus) was identified at Laguna Atascosa National Wildlife Refuge on the lower Texas coast, extending its known breeding distribution farther south than previously described. We studied this breeding population of Texas Seaside Sparrows from April 2012–January 2013 on the Laguna Atascosa National Wildlife Refuge to obtain population density estimates and describe habitat associations. We estimated seasonal density during one year using a distance sampling approach. We described plant community characteristics and estimated percent ground cover. Density estimates of Seaside Sparrows by season were 3.49/ha (CV = 8.27) for spring, 3.59/ha (CV = 18.16) for summer, 4.07/ha (CV = 9.69) for fall, and 1.91/ha (CV = 21.92) for winter. The dominant plant species along the intertidal zone transect where Seaside Sparrows were detected included turtleweed (aka saltwort; Batis maritima), saltgrass (Distichlis spicata), and bushy seaside t...

Survey for ticks on feral swine within a cattle fever tick-infested landscape in Texas, U.S.A.

We collected ticks from feral swine, Sus scrofa L., during 1–3 September 2015, in pastures known to be infested by southern cattle ticks, Rhipicephalus (Boophilus) microplus (Canestrini), at the Laguna Atascosa National Wildlife Refuge in Cameron County, Texas, U.S.A. All 81 examined feral swine were infested by ticks, but none was infested by R. microplus. Tick species collected were Amblyomma maculatum Koch, Amblyomma mixtum Koch, Amblyomma tenellum Koch, Dermacentor halli McIntosh, and Dermaentor variabilis (Say). This is the first formal report of A. tenellum infesting feral swine.

Loss of genetic diversity among ocelots in the United States during the 20th century linked to human induced population reductions.

Ocelots (Leopardus pardalis) in the United States currently exhibit low levels of genetic diversity. One hypothesis for this observation is that habitat fragmentation, resulting from human induced changes in the landscape during the 20th century, created island populations with highly reduced gene flow and increased genetic drift and inbreeding. In an effort to investigate this, we used a portion of the mitochondrial control region and 11 autosomal microsatellite loci to examine historical levels of genetic diversity and infer temporal changes in ocelot populations between 1853 and 2005. Levels of genetic diversity were higher in historical ocelot populations than in extant populations from Texas. The earliest documented loss of mitochondrial haplotype diversity occurred at Laguna Atascosa National Wildlife Refuge. The second extant population inhabiting private lands in Willacy County retained higher levels of genetic diversity through the 1990s, but subsequently lost diversity over the next decade. A similar pattern was observed for autosomal microsatellite loci. This supports the argument that low levels of genetic diversity in Texas are related to human induced population reductions and fragmentation, both of which threaten the remaining ocelots in the United States. At this time, the best means of mitigating the continued erosion of genetic variation are translocation of individuals either from larger populations in Mexico to Texas, or between the Texas populations.

Reduced genetic diversity and isolation of remnant ocelot populations occupying a severely fragmented landscape in southern Texas

The ocelot Leopardus pardalis has become a conservation priority in the US as a result of severe population decline and loss of habitat during the 20th century. Only two small populations remain in this country. Their short-term viability is threatened by the disappearance of dense thornshrub communities, human-caused mortality and demographic stochasticity. The influence these factors have on ocelot persistence must be considered to develop effective conservation initiatives. We therefore examined neutral genetic diversity and connectivity among ocelots in the US and northeastern Mexico using 25 autosomal microsatellites and a 395-bp segment of the mitochondrial control region. Genetic variation was lowest in the population occurring on Laguna Atascosa National Wildlife Refuge, Texas (autosomal microsatellite HE = 0.399 and mtDNA-haplotype diversity = 0) and highest in northeastern Mexico (0.637 and 0.73, respectively), while intermediate on private lands in Willacy County, Texas (0.553 and 0.252, respectively). Significant genetic differentiation between the two Texas populations was observed, despite their close proximity (� 30 km). Both populations were also significantly divergent from northeastern Mexico. The absence of any detectable gene flow implies that the human modified landscape of the Lower Rio Grande Valley in southern Texas acts as a strong barrier to ocelot movement, disrupting metapopulation dynamics and contributing to loss of diversity. As a consequence, continued genetic erosion among the Texas populations is expected. The lack of movement through the fragmented landscape also suggests it is unlikely ocelots will recolonize unoccupied habitat patches along the Lower Rio Grande and the delta interior where agriculture and urban land uses predominate. The continued rapid development will exacerbate this problem. These factors threaten the persistence of the Texas populations and limit their recovery. Translocations are necessary to link ocelot populations in the US.

Wild-reared aplomado falcons survive and recruit at higher rates than hacked falcons in a common environment

The northern aplomado falcon ( Falco femoralis septentrionalis) has been the subject of a large-scale reintroduction effort conducted by The Peregrine Fund since 1993. Intensive monitoring during 2002–2004 revealed approximately 38 breeding pairs and numerous non-territorial individuals in two study areas centered on Matagorda Island National Wildlife Refuge (NWR) and Laguna Atascosa NWR. Continued releases (“hacking”) of captive-bred young after pair establishment and successful wild breeding provided an opportunity to compare survival and recruitment histories of wild-reared and hacked falcons hatched during 2001–2003. We used Program MARK to rank multi-state models of apparent survival and recruitment rates with Akaike’s Information Criterion scores, corrected for small samples. The top model candidate, with almost 3.5 times more support than the next best model, detected differences due to falcon origin (wild or captivity): although breeder survival was independent of origin, juvenile hacked falcons survived and recruited at lower rates than wild-reared falcons. Given the high density of territorial adult falcons in the study areas, the difference in apparent survival may reflect greater dispersal by hacked falcons, increased tolerance of wild falcons in territory margins due to prior socialization, or other factors effecting higher intrinsic fitness of wild falcons. However, natal dispersal did not differ between the two groups, strengthening the hypothesis of a difference in true survival. Disproportionately greater recruitment of wild falcons into the breeding population again suggests their higher intrinsic fitness. These findings show how close monitoring of population vital rates can efficiently guide adaptive management of recovering populations.

Aspects of the biology of Salicornia bigelovii Torr. in relation to a proposed restoration of a wind-tidal flat system on the south Texas, USA coast

Wind-tidal flats are the dominant coastal wetland type in southern Texas, USA. Succulent vascular plants are colonizing the flats in some locations, often where past dredge disposal along navigation channels and other activities have interrupted natural water communication between hypersaline bays and large areas of wind-tidal flats. The objective of this study was to test the feasibility of proposed removal of a causeway at Laguna Atascosa National Wildlife Refuge to restore the historic hydrologic regime and eradicate encroaching vascular plants, mostly Salicornia bigelovii, on the assumption that high sediment salt excluded these vascular plants under natural conditions. Assessment in spring 1998 of the density of Salicornia in relation to elevation and sediment salt of bare and vegetated zones on the vegetated flats on one side of the causeway and entirely barren flats with unimpaired connection to Laguna Madre on the other side of the causeway suggested that sediment salt > 0.1 g ml−1 excluded vascular plants. However, bimonthly sampling in 1999–2000 revealed that sediment salt concentrations were > 0.1 g ml−1 throughout the vegetated zone in July and more locally in the period of winter low water, with little impairment to established plants. This indicates that if control is desired, it must be exerted at germination and early establishment during and after fall high water. Continuous monitoring of water levels on either side of the causeway suggests that, even with removal of the causeway, flooding with hypersaline lagoon water will be too infrequent to counteract the freshening effect of a permanent hydraulic connection to the main agricultural drain of the lower Rio Grande Valley that has developed at the other end of the salt flat. Monitoring Salicornia distribution over six years documented huge variation between years but no trend toward increasing dominance of the flats. The results of this study illustrate that the most obvious alterations to a site may not be the most influential on function and that the scale of analysis may have to extend far beyond the site in space and time to evaluate a proposed restoration properly.

Use of scented hair snares to detect ocelots

Biologists need a variety of tools to determine the population and genetic status of the ocelot (Leopardus pardalis), an elusive Neotropical cat that favors dense habitats. We developed and tested a technique that entices ocelots to rub on scented hair snares and uses DNA analysis of the hair to determine species, gender, and individual identity. Twenty-seven (84%) of 32 captive ocelots rubbed against the scented pads. In field tests at Laguna Atascosa National Wildlife Refuge in south Texas, we detected a minimum of 6 ocelots, including at least 3 of 4 radiocollared animals. Using a 6-locus microsatellite analysis, we made individual identification for 10 of 20 samples. Scented hair snares can provide useful information on the population and genetic status of ocelots and identification of key areas and connecting linkages. We suggest that surveys for ocelots deploy 1 station per 25–50 ha and check them every 1–2 weeks.

Potential Effects of Environmental Contaminants on Recovery of the Aplomado Falcon in South Texas

Efforts to reintroduce the aplomado falcon (Falco femoralis) into its former range in the southern part of Texas began in 1977. Not until 1993, however, were a significant number (26) of fledgling aplomado falcons released. The first nesting pair of aplomado falcons was reported near the Brownsville Ship Channel during 1995. Because of a long history of pesticide use in the Lower Rio Grande Valley, during 1993-94 we investigated the accumulation of environmental contaminants in plasma of aplomado falcons released at the Laguna Atascosa National Wildlife Refuge. We also assessed the potential contribution of typical prey species to aplomado falcon contaminant burdens. Organochlorine pesticides and PCBs were below detection limits (wet wt basis) in plasma; however, some organochlorines including 1.75 and 1.41 μg/g p,p'-DDE, and 0.49 and 1.52 μg/g total PCBs were detected in addled eggs collected in 1995 and 1996. Mercury also was detected at 1.5 and 4.1 μg/g dry weight in the addled eggs collected in 1995 and 1996. We detected DDE (range 0.02-0.25 μg/g) in carcasses of potential prey of the aplomado falcon. Trace metals also were detected in potential prey at levels which are not of concern, except for Hg, which was high in a few meadowlarks. Low levels of DDE and most trace metals in potential prey, including mourning doves (Zenaida macroura) and eastern meadowlarks (Sturnella magna), are not likely to result in adverse effects on the aplomado falcon in the Lower Rio Grande Valley. However, elevated Hg residues in meadowlarks (in a few cases) and potentially higher DDE levels in other prey species such as the great-tailed grackle (Quiscalus mexicanus) could result in negative effects on reproduction and survival of some aplomado falcons in south Texas.

Long-Lived Pollutants in Sediments from the Laguna Atascosa National Wildlife Refuge, Texas

DDT and some heavy metals are long-lived pollutants which may be retained in sedimentary layers and may be relocated by post-depositional biological or mechanical processes. Because DDT has a half life of up to 17 yr and it is concentrated in higher ecological levels, even a few parts per billion in the sedimentary substrate can be harmful to wildlife. The potential danger and the persistence of many long-lived pollutants create a genuine need for environmental studies made by geologists.

The Masked Duck in the United States

UNTIL fairly recently, the neotropical Masked Duck (Oxyura dominica) had been reported within the continental United States only a few times. Between 1857 and 1905 single accidental records of the species were made in Vermont, Massachusetts, Wisconsin, and Maryland (Bent, 1925). Only the Rio Grande area of Cameron County, Texas, where Fisher (1895) first reported the sighting of several Masked Ducks and the collection of a female specimen near Brownsville in July 1891, has been considered a potential breeding locality. Griscom and Crosby (1925) mention a male specimen, taken in the same place at the same time, and Lawrence (1927) reports a specimen killed in Brazoria County, Texas. A female Masked Duck was shot in Louisiana during December of 1933 (Lowery, 1955), one was reported near Harlingen (Cameron County), Texas in December of 1936 (Bird-Lore, 39': 65, 1937), and a flock of 24 was reported at Aransas National Wildlife Refuge (Aransas County), Texas in December of 1948 (Audubon Field Notes, 3: 177, 1949). As Masked Ducks are not known ever to have been kept in captivity in the United States (Delacour, 1959), it is unlikely that these early records represent escaped birds. In September 1937 Lo-etscher (1956) observed a group of eight Masked Ducks near Brownsville, including two males in nuptial plumage. Loetscher presumed that the five female-like birds may have included young of both sexes. Prior to 1941 L. I. Davis repeatedly observed single Masked Ducks near Harlingen, and, although no nest was located, he believed (1966) that they attempted to breed there in 1941, when five possible immatures were seen. These two cases apparently represent the only reported instances of possible breeding by Masked Ducks in the United States prior to 1967. During the 195Os three Masked Ducks were reported from Florida, including a bird found dead at Key West in 1955 (Hames, 1956), one shot during the 1956-57 hunting season in Glades County, and one shot during 1957 in Palm Beach County (Owre, 1962). Texas reports include a female seen near Santa Ana National Wildlife Refuge (Hidalgo County) during March of 1957 (A.F.N., 11: 362, 1957) and a female observed on Laguna Atascosa National Wildlife Refuge (Cameron County) in October of 1959 (A.F.N., 14: 53, 1960). The early 1960s brought about a surprising number of new Masked Duck reports, often shortly after the passage of Caribbean hurricanes. These included the sighting of a male on Brigantine National Wildlife Refuge, New Jersey, in December 1960 (A.F.N., 15: 315, 1961), a bird