Papers by Fidel Hernandez
tarleton.edu
An increasingly common practice in southern Texas is baiting roads with grain to facilitate north... more An increasingly common practice in southern Texas is baiting roads with grain to facilitate northern bobwhite (Colinus virginianus) harvest. Unfortunately, such a practice has the potential to negatively affect bobwhite survival and covey home range size, especially during relatively dry periods. However, the pattern of baiting (i.e., single road vs. multiple road baiting) could influence how baiting of roads affects bobwhites. The objective of the project was to document the effects of multiple-road baiting on bobwhite survival and movements in contrast to baiting only a single road. The project involved two study sites in Jim Hogg County, Texas (one area with a single baited road and one area with multiple baited roads) which were monitored over 3 periods, pre-baiting (Sep -Oct), baiting (Nov -Dec), and post-baiting (Jan -Feb). Bobwhite survival, home range size, and predator abundance was assessed for each area. Bobwhite survival and home range size and predator abundance did not differ between the two baiting patterns. However, during dry conditions, baiting multiple roads in a pasture may be less detrimental to the survival of bobwhite populations than just baiting one road in a pasture.
Wildlife Society Bulletin, 2004
EFFECTS OF HURRICANE BRET ON NORTHERN BOBWHITE SURVIVAL IN SOUTH TEXAS
The impacts of intense storms such as hurricanes on wildlife rarely are documented. We had the op... more The impacts of intense storms such as hurricanes on wildlife rarely are documented. We had the opportunity to monitor the impact of Hurricane Bret on northern bobwhite (Colinus virginianus) survival and reproduction in Brooks County, Texas. On 22 August 1999, Hurricane Bret struck our study area, which received 45 cm of rain and experienced wind gusts 160 km/h. We documented
Journal of Wildlife Management, 2006
plans. Unfortunately, many recovery plans are limited in effectiveness because they suffer from v... more plans. Unfortunately, many recovery plans are limited in effectiveness because they suffer from various limitations; one of which is the lack of scientific data. Because recovery plans for endangered species are inherently plagued by lack of biological data of focal species, new approaches are warranted in recovery-plan development to use what little data are available more effectively. The use of academic-agency partnerships has been suggested as a means to accomplish this objective; academics contribute scientific knowledge, and agency personnel contribute federal regulation expertise. We used the masked bobwhite (Colinus virginianus ridgwayi), the only endangered quail in North America, as a case study to illustrate how such partnerships can be employed to incorporate the latest scientific knowledge into recovery planning. Because the case study of the masked bobwhite embodies many of the difficulties associated with endangered species recovery (e.g., lack of biological data, limited personnel, limited resources), our approach to linking biology, ecology, and management can serve as a general model for recovery planning of other endangered species. We began with a comprehensive review and synthesis of masked bobwhite literature.
Years of research on the nesting ecology of the northern bobwhite ( Colinus virginianus ) have do... more Years of research on the nesting ecology of the northern bobwhite ( Colinus virginianus ) have documented the use of bunchgrasses as common nesting cover. However, in the Rolling Plains of Texas, recent studies indicate a relatively high use of prickly pear cactus ( Opuntia spp.) as suitable nesting cover. To explain this previously unreported use of prickly pear, we evaluated 2 hypotheses: ( 1 ) the limited-bunchgrass, and ( 2 ) nest-protection hypotheses. We speculated that bobwhites nested in prickly pear cactus because of low availability of bunchgrasses and/or structural protection against predators. We radiomarked 218 bobwhites during spring and summer of 1997 and 1998 on 4 sites in Shackelford County, Texas, USA. Bobwhites nested in prickly pear despite adequate bunchgrass cover ( >600 potential nesting sites/ha). Of 81 nests located, 12%were in shrubs (e.g., catclaw [ Acacia greggii ]), 30%were in prickly pear, and 58%were in bunchgrass. Nest success did not differ among nesting substrates ( χ 2 = 2 . 1 , df = 2 , P = 0 . 35 ) but was dependent on the degree of protection provided by the nesting substrate ( χ 2 = 16 , df = 2 , P = 0 . 001 ). However, successful nests also had a higher density of bunchgrasses in the surrounding area than unsuccessful nests ( P = 0 . 001 ). Our data partially supported the nest-protection hypothesis and did not support the limited-bunchgrass hypothesis.
Journal of Wildlife Management, 2006
We evaluated an unverified index (auditory counts) used to estimate breeding populations of white... more We evaluated an unverified index (auditory counts) used to estimate breeding populations of white-winged doves (Zenaida asiatica) in Texas, USA. Our objectives were to determine optimal survey time of day, year, and count duration, determine if a relationship existed between number of calling doves and population size (nest and dove density), and evaluate an electronic counter to estimate breeding density. We collected data on 15 sites in the Lower Rio Grande Valley of Texas during May-August of [2002][2003]. Peak calling occurred between mid-May and late June during 0600-0800 hours. We detected about 60% of calling doves during 2-minute auditory counts. Estimates of breeding doves (pairs ha À1 ) as determined by auditory counts were positively correlated with both population density (r . 0.90, P , 0.01) and nest density (r . 0.94, P , 0.01). The electronic coo-counter tally also exhibited a positive relationship with population density (r . 0.77, P , 0.01) and nest density (r . 0.92, P , 0.04). However, the high correlations observed for auditory counts and electronic counter were influenced by 2 high dove-density sites. Our data did not provide convincing support for the premise underlying auditory counts of white-winged doves (i.e., number of doves calling reflects dove abundance). The electronic coo counter was limited in application because it tabulated dove calls based solely on acoustic frequency and therefore could not discriminate against other avian calls with acoustic frequencies similar to those of white-winged doves. Auditory counts may be appropriate as coarse-resolution reconnaissance surveys to locate new whitewinged dove areas in need of monitoring but not to obtain reliable abundance estimates. The use of an electronic counter to estimate breeding populations of white-winged doves holds promise, given technical modifications, and warrants further research. Given the current limitations of both auditory counts and electronic counters, alternative survey methods that incorporate detection probabilities (e.g., distance sampling) need to be evaluated for white-winged doves.
Texas Parks and Wildlife Department (TPWD) has used auditory call counts annually since 1949 to m... more Texas Parks and Wildlife Department (TPWD) has used auditory call counts annually since 1949 to monitor white-winged dove (Zenaida asiatica) populations in the Lower Rio Grande Valley of Texas. Recently, white-winged doves have been expanding their distribution, and now the largest populations occur in urban areas north of their historic south Texas range. It has become necessary to develop an urban survey method to better monitor these populations. We compared two call count sampling methods for surveying white-winged doves in urban environments (i.e., transects vs. grid-points in Austin during and San Antonio during 2001. We also determined the percent annual population change we were able to detect for each year with the current sample size using the grid-point survey method. Estimates of whitewinged dove breeding density were higher using the transect method compared to the grid method each year. Power analysis indicated that with current sample sizes in each city, we were able to detect between a 20% and 30% annual change in mean population density in both Austin and San Antonio. We conclude the grid method can be more effective at reflecting the spatial distribution of white-winged doves in urban areas than the original transect approach. The grid method should be improved to reduce variance if it is to be used in the future. Accuracy of survey methods were not evaluated here. To obtain more reliable estimates of density, other methods such as distance sampling should be evaluated.
Wildlife Society Bulletin, 2004
Wildlife Society Bulletin, 2005
Northern bobwhite (Colinus virginianus) populations in southwestern rangelands are influenced by ... more Northern bobwhite (Colinus virginianus) populations in southwestern rangelands are influenced by precipitation; populations increase during relatively wet periods and decrease during drought. Understanding the demographic responses of bobwhites to fluctuations in precipitation might provide a basis for identifying mechanisms responsible for the phenomenon. We compared 10 population variables (bobwhite survival, nestingseason length, nest success, hen success, percent hens nesting and renesting, nesting rate, percent juveniles in fall harvest sample (Nov-Feb), clutch size, and egg hatchability) between a dry (Sep 2000-Aug 2001; 51 cm precipitation) and wet period (Sep 2002-Aug 2003 93 cm precipitation) in Brooks County, Texas. We monitored radiomarked bobwhites on 3 sites during the dry (n=263 bobwhites) and wet period (n=191 bobwhites) to obtain estimates of survival and reproductive effort. Bobwhite survival curves differed between the dry period (0.30±0.04; S±SE, n=102 bobwhites) and wet period (0.60± 0.06; n = 71 bobwhites; P<0.001) during fall-winter (Sep-Feb). A lower proportion of hens nested during the dry period (95% Cl: 52.6+22.5 %; n=19 hens) compared to the wet period (100%; n=15 hens). Of hens that nested, the dry period exhibited a lower nesting rate (95% Cl: 1.2±0.3 nests/hen) compared to the wet period (95% Cl: 2.3±0.5 nests/hen). The dry period also experienced a shorter nesting season (69 days) compared to wet period (159 days). Lastly, percent juveniles (Nov-Feb) was lower during the dry period (95% Cl: 69.3+0.3 %; n=740 harvested bobwhites) compared to wet period (95% Cl: 78.3±2.1%; n=1,415 harvested bobwhites). Our field study highlights 4 demographic variables (i.e., survival, percentage of hens nesting, nesting rate, and nesting-season length) that warrant further research to identify causal factors responsible for the boom-and-bust phenomenon in bobwhites. Further, our data suggest that drought negatively impacts bobwhite reproductive effort such that harvest should be reduced or ceased during drought (e.g., <50 cm annual precipitation).
Journal of Wildlife Management, 2007
Distance sampling has been identified as a reliable and well-suited method for estimating norther... more Distance sampling has been identified as a reliable and well-suited method for estimating northern bobwhite (Colinus virginianus) density. However, distance sampling using walked transects requires intense sampling to obtain precise estimates, thus making the technique impractical for large acreages. Researchers have addressed this limitation by either resorting to the use of indices (e.g., morning covey-call surveys) or incorporating the use of aerial surveys with distance sampling. Both approaches remain relatively untested. Our objectives were to 1) compare density estimates among morning covey-call surveys, helicopter transects, and walked transects; 2) test a critical assumption of distance sampling pertinent to helicopter surveys (i.e., all objects on line are detected); and 3) evaluate the underlying premise of morning covey-call surveys (i.e., that the no. of calling coveys correlates with bobwhite density). Our study was conducted on 3 study sites in Brooks County, Texas, USA, during October to December, 2001December, to 2005. Comparisons between walked transects and morning covey-call surveys involved the entire 5-year data set, whereas helicopter transects involved only the latter 2 years. Density estimates obtained from helicopter transects were similar to walked transect estimates for both years. We documented a detection probability on the helicopter transect line of 70 6 10.2% (% 6 SE; n ¼ 20 coveys). Morning covey-call surveys yielded similar density estimates to walked transect estimates during only 2 of 5 years, when walked transect estimates were the least accurate and precise. We detected a positive relationship (R 2 ¼ 0.51; 95% CI for slope: 29.5-53.1; n ¼ 63 observations) between covey density and number of coveys heard calling. We conclude that helicopter transects appear to be a viable alternative to walked transects for estimating density of bobwhites. Morning covey-call surveys appear to be a poor method to estimate absolute abundance and to depict general population trajectories.
Journal of Wildlife Management, 2007
Northern bobwhite (Colinus virginianus) is a species for which extensive knowledge exists regardi... more Northern bobwhite (Colinus virginianus) is a species for which extensive knowledge exists regarding its ecology, life history, and habitat. Although the qualitative aspects of bobwhite habitat have been described and known for many decades, researchers have neglected to characterize bobwhite habitat quantitatively (i.e., habitat selection). Thus, biologists have been capable of identifying components that compose bobwhite habitat but have only been able to speculate on how much of each component was necessary. We documented selectionavoidance behavior of nesting bobwhites in Brooks County, Texas, USA, during May-August, 2004-2005. We measured 5 vegetation features (i.e., nesting-substrate ht and width, suitable nest clump density, herbaceous canopy coverage, and radius of complete visual obstruction) at nest sites (n ¼ 105) and at random points (n ¼ 204). We used continuous selection functions to assess habitat use and identify bounds of suitability. Selection domains for nesting-substrate height and radius of complete visual obstruction were 16.9-31.2 cm and 1.05-4.35 m, respectively. Across all measurements, bobwhites selected for nest sites with a nesting-substrate width !22.4 cm, suitable nest-clump density !730 nest clumps/ha, and herbaceous canopy coverage !36.7%. This knowledge will provide an important foundation for managers to evaluate current nesting conditions on semiarid rangelands and provide a basis for habitat management aimed at creating suitable nesting habitat for bobwhites.
Wilson Journal of Ornithology, 2006
A long-term (Ͼ5 years) study of Northern Bobwhite (Colinus virginianus) provided the first record... more A long-term (Ͼ5 years) study of Northern Bobwhite (Colinus virginianus) provided the first record of runt eggs and two observations of prolonged incubation. During 2004, we located two clutches (n ϭ 11 and 9 eggs)-laid by the same henconsisting entirely of runt eggs. Mean length, width, and mass were 18.8 mm, 15.4 mm, and 2.0 g, respectively, 26% of the volume and 24% of the mass of typical bobwhite eggs. Based on our long-term data set for bobwhites (n ϭ 3,566 eggs), runt eggs occur at a frequency of 0.56%, within the range (0.02-4.32%) reported for other avian species. The two records of prolonged incubation behavior represented 75 days (326%) and 47 days (204%) beyond the normal incubation period (23 days) of bobwhites. This prolonged incubation behavior is in excess of the time frame reported for most birds exhibiting prolonged incubation (50-100% beyond normal incubation).
NEST-SITE SELECTION AND NEST SURVIVAL OF NORTHERN BOBWHITE IN SOUTHERN TEXAS
Wilson Journal of Ornithology, 2007
Abstract We examined abiotic and biotic variables potentially associated with Northern Bobwhite (... more Abstract We examined abiotic and biotic variables potentially associated with Northern Bobwhite (Colinus virginianus) nest-site selection and nest success in southern Texas, USA during 2002-2005. These data were used to characterize bobwhite nest-site selection, ...
Journal of Wildlife Management, 2007
Predation is the primary cause of nest failure for northern bobwhites (Colinus virginianus). Ther... more Predation is the primary cause of nest failure for northern bobwhites (Colinus virginianus). There are few reliable data documenting the species diversity and relative importance of bobwhite nest predators in southern Texas, USA. We used infrared videomonitoring systems to document nest fates of 127 bobwhite nests over 4 nesting seasons from 2002 to 2005 in southern Texas. A majority of depredation events (83%) were caused by 4 species: coyote (Canis latrans), striped skunk (Mephitis mephitis), southern fire ant (Solenopsis xyloni), and badger (Taxidea taxus). Observed bobwhite nest fates for the study period were 0.50 successful, 0.34 depredated, and 0.16 abandoned or undetermined. A universal approach to mitigating nest predation is not likely to be applicable in regions similar to southern Texas, with high nest-predator diversity (e.g., fire ants, rodents, and mammalian carnivores). We believe that infrared video surveillance is a valuable tool for documenting baseline information on predator context and nest fate for many avian species, considering the limitations of past
EFFECTS OF INVASIVE EXOTIC GRASSES ON SOUTH TEXAS RANGELAND BREEDING BIRDS
Auk, 2006
Abstract Invasive exotic plants are a major threat to many species of wild birds. When these plan... more Abstract Invasive exotic plants are a major threat to many species of wild birds. When these plants become established and widespread, the floristic composition of native plant communities becomes simplified, which can result in long-term and often irreversible ...
Invasive Plant Science and Management, 2009
Since the 1950s, many south Texas rangelands have been seeded with buffelgrass, a perennial C 4 b... more Since the 1950s, many south Texas rangelands have been seeded with buffelgrass, a perennial C 4 bunchgrass native to Africa that is believed to contribute to reductions in biodiversity. Forb species represent a critical habitat component throughout the breeding period for many wildlife species as seed (summer to fall), as green vegetative material (spring to summer), and as habitat for arthropods (spring to summer). Reductions in richness and diversity of crucial ecosystem components such as forbs and arthropods have large implications for grassland birds and other wildlife. We sampled annual and perennial forbs within 1-m 2 quadrats on 15 study plots (1 ha; n 5 20 quadrats/plot) at Chaparral Wildlife Management Area, in LaSalle and Dimmit counties, Texas, during 2005 and 2006. Study plots were divided into five light-buffelgrass plots (0 to 5% buffelgrass canopy coverage), five moderate-buffelgrass plots (5 to 25% buffelgrass canopy coverage), and five heavy-buffelgrass plots (. 25% buffelgrass canopy coverage). Buffelgrass in study plots was composed of naturalized plants, and was not deliberately planted. During 2005 we observed that plots with . 25% buffelgrass had a 73% reduction in forb canopy of native species, a 64% reduction in native forb species richness, and a 77% reduction in native forb stem density compared to plots with 0 to 5% buffelgrass. These trends in native forb reduction (279% native forb canopy, 265% forb species richness, 280% forb stem density) were nearly identical in 2006, even with greatly reduced rainfall. Simple linear regression revealed negative relationships between buffelgrass cover, total exotic grass cover (buffelgrass and Lehmann lovegrass), and total grass cover and the richness, coverage, and density of forbs/m 2 . Reductions in diversity may have larger implications regarding ecosystem function and available useable space and densities of desired bird species such as northern bobwhite. Nomenclature: Buffelgrass, Pennisetum ciliare (L.) Link; Lehmann lovegrass, Eragrostis lehmanniana Nees.
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Papers by Fidel Hernandez