Geology topics

H.F. Percival

Publications and source records attributed to H.F. Percival.

13 recordsLinked to original sources

USGS2012

Diet of the invasive Cuban treefrog (Osteopilus septentrionalis) in pine rockland and mangrove habitats in South Florida

Native to Cuba, the Bahamas and the Cayman Islands, the Cuban Treefrog (CTF) is an invasive species in Florida, with the ability to inflict serious ecological damage to invaded habitats. By examining the diet of the CTF, a known predator of native frogs, better predictions may be made of the impacts on native species and ecosystems. From 2002 - 2003, CTF diet was investigated in south Florida at four sites, two each within pine rockland and mangrove habitat. Within each habitat, one site exhibited a low density of CTFs and the other a high density of CTFs. CTFs were captured in PVC pipes attached to trees and stomach contents were examined after euthanasia. Beetles were the most numerous and widely consumed prey item among sites; roaches, orthopterans, spiders, ants, and caterpillars were also major dietary components. There were significant differences in the proportion of taxa consumed by CTFs between low and high density populations within each habitat, with the low density site in every instance having the higher proportion. Across habitats, ants comprised a significantly higher proportion of the diet in mangroves, whereas beetles, orthopterans, and snails comprised a significantly higher proportion of the diet in pine rocklands. Approximately 3.5% of all stomachs examined contained anuran remains. Though not significant, CTFs from low density sites consumed a higher proportion of frogs than those at high density sites. Corroborating previous research, the data show the CTF to be a generalist feeder, consuming a wide variety of invertebrate prey, with anurans playing only a minor role in the overall diet.

Florida↗

USGS2010

Possible generational effects of habitat degradation on alligator reproduction

Population decline of the American alligator (Alligator mississippiensis) was observed in Lake Apopka in central Florida, USA, in the early 1980s. This decline was thought to result from adult mortality and nest failure caused by anthropogenic increases in sediment loads, nutrients, and contaminants. Reproductive impairment also was reported. Extensive restoration of marshes associated with Lake Apopka has been conducted, as well as some limited restoration measures on the lake. Monitoring by the Florida Fish and Wildlife Conservation Commission (FFWCC) has indicated that the adult alligator population began increasing in the early 1990s. We expected that the previously reported high proportion of complete nest failure (??0) during the 1980s may have decreased. We collected clutches from alligator nests in Lake Apopka from 1983 to 2003 and from 5 reference areas from 1988 to 1991, and we artificially incubated them. We used a Bayesian framework with Gibbs sampler of Markov chain Monte Carlo simulation to analyze ??0. Estimated ??0was consistently higher in Lake Apopka compared with reference areas, and the difference in ??0 ranged from 0.19 to 0.56. We conducted change point analysis to identify and test the significance of the change point in ??0in Lake Apopka between 1983 and 2003, indicating the point of reproductive recovery. The estimated Bayes factor strongly supported the single change point hypothesis against the no change point hypothesis. The major downward shift in ??0 probably occurred in the mid-1990s, approximately a generation after the major population decline in the 1980s. Furthermore, estimated ??0 values after the change point (0.21) were comparable with those of reference areas (0.07-0.31). These results combined with the monitoring by FFWCC seem to suggest that anthropogenic habitat degradation caused reproductive impairment of adult females and decreases in ??0 occurred with the sexual maturity of a new generation of breeding females. Long-term monitoring is essential to understand population changes due to habitat restoration. Such information can be used as an input in planning and evaluating restoration activities.

Journal of Wildlife Management↗

USGS2010

The persistence of endangered Florida Salt Marsh Voles in salt marshes of the central Florida Gulf Coast

Two endangered Microtus pennsylvanicus dukecampbelli (Florida Salt Marsh Vole) were captured at a new location, in February of 2009, at Lower Suwannee National Wildlife Refuge. Since the species discovery in 1979, only 43 Florida Salt Marsh Voles (hereafter FSM Vole) have been captured. Outside of the type locality, this is only the second documented location for the FSM Vole. Given the difficulty in trapping this species and the lack of information about its life history, its discovery in a new location lends itself to the possibility that it is more widespread in the Central Florida Gulf Coast than previously thought. Although much of the salt marsh in the area is in public ownership, a good deal of it has already been altered by logging or development and is threatened by global climate change. More research is needed to adequately protect and manage the habitat for the FSM Vole. A study of FSM Vole coastal salt marsh habitat could also serve as a valuable monitoring tool for subtle changes in salt marsh habitats as global climate change progresses.

Southeastern Naturalist↗

USGS2008

Modeling the effect of toe clipping on treefrog survival: Beyond the return rate

Some studies have described a negative effect of toe clipping on return rates of marked anurans, but the return rate is limited in that it does not account for heterogeneity of capture probabilities. We used open population mark-recapture models to estimate both apparent survival ( ϕ ) and the recapture probability ( p ) of two treefrog species individually marked by clipping 2–4 toes. We used information-theoretic model selection to examine the effect of toe clipping on survival while accounting for variation in capture probability. The model selection results indicate strong support for an effect of toe clipping on survival of Green Treefrogs ( Hyla cinerea ) and only limited support for an effect of toe clipping on capture probability. We estimate there was a mean absolute decrease in survival of 5.02% and 11.16% for Green Treefrogs with three and four toes removed, respectively, compared to individuals with just two toes removed. Results for Squirrel Treefrogs ( Hyla squirella ) indicate little support for an effect of toe clipping on survival but may indicate some support for a negative effect on capture probability. We believe that the return rate alone should not be used to examine survival of marked animals because constant capture probability must be assumed, and our examples demonstrate how capture probability may vary over time and among groups. Mark-recapture models provide a method for estimating the effect of toe clipping on anuran survival in situations where unique marks are applied.

Journal of Herpetology↗

USGS2008

Dry down impacts on apple snail (Pomacea paludosa) demography: Implications for wetland water management

Florida apple snails (Pomacea paludosa Say) are prey for several wetland-dependent predators, most notably for the endangered Florida snail kite (Rostrhamus sociabilis Vieillot). Management concerns for kites have been raised regarding the impacts of wetland dry downs on snails, but little data exists to validate these concerns. We simulated drying events in experimental tanks, where we observed that snail survival patterns, regardless of hydrology, were driven by a post-reproductive die off. In contrast to earlier reports of little to no dry down tolerance, we found that 70% of pre-reproductive adult-sized snails survived a 12-week dry down. Smaller size classes of snails exhibited significantly lower survival rates (< 50% after eight weeks dry). Field surveys showed that 77% of egg production occurs in April-June. Our hydrologic analyses of six peninsular Florida wetlands showed that most dry downs overlapped a portion of the peak snail breeding season, and 70% of dry downs were ??? 12 weeks in duration. Dry down timing can affect recruitment by truncating annual egg production and stranding juveniles. Dry down survival rates and seasonal patterns of egg cluster production helped define a range of hydrologic conditions that support robust apple snail populations, and illustrate why multiple characteristics of dry down events should be considered in developing target hydrologic regimes for wetland fauna. ?? 2008, The Society of Wetland Scientists.

Wetlands↗

USGS2007

Alligator diet in relation to alligator mortality on Lake Griffin, FL

Alligator mississippiensis (American Alligators) demonstrated low hatch-rate success and increased adult mortality on Lake Griffin, FL, between 1998 and 2003. Dying Lake Griffin alligators with symptoms of poor motor coordination were reported to show specific neurological impairment and brain lesions. Similar lesions were documented in salmonines that consumed clupeids with high thiaminase levels. Therefore, we investigated the diet of Lake Griffin alligators and compared it with alligator diets from two lakes that exhibited relatively low levels of unexplained alligator mortality to see if consumption of Dorosoma cepedianum (gizzard shad) could be correlated with patterns of mortality. Shad in both lakes Griffin and Apopka had high levels of thiaminase and Lake Apopka alligators were consuming greater amounts of shad relative to Lake Griffin without showing mortality rates similar to Lake Griffin alligators. Therefore, a relationship between shad consumption alone and alligator mortality is not supported.

Southeastern Naturalist↗

USGS2007

Scale-dependent habitat selection of nesting Great Egrets and Snowy Egrets

Foraging habitat selection of nesting Great Egrets (Ardea alba) and Snowy Egrets (Egretta thula) was investigated within an estuary with extensive impounded salt marsh habitat. Using a geographic information system, available habitat was partitioned into concentric bands at five, ten, and 15 km radius from nesting colonies to assess the relative effects of habitat composition and distance on habitat selection. Snowy Egrets were more likely than Great Egrets to depart colonies and travel to foraging sites in groups, but both species usually arrived at sites that were occupied by other wading birds. Mean flight distances were 6.2 km (SE = 0.4, N = 28, range 1.8-10.7 km) for Great Egrets and 4.7 km (SE = 0.48, N = 31, range 0.7-12.5 km) for Snowy Egrets. At the broadest spatial scale both species used impounded (mostly salt marsh) and estuarine edge habitat more than expected based on availability while avoiding unimpounded (mostly fresh water wetland) habitat. At more local scales habitat use matched availability. Interpretation of habitat preference differed with the types of habitat that were included and the maximum distance that habitat was considered available. These results illustrate that caution is needed when interpreting the results of habitat preference studies when individuals are constrained in their choice of habitats, such as for central place foragers.

Waterbirds↗

USGS2005

Raccoon removal reduces sea turtle nest depredation in the Ten Thousand Islands of Florida

Predation by raccoons, Procyon lotor marinus (L.), is the primary cause of sea turtle nest loss in the Ten Thousand Islands archipelago. Four islands within Ten Thousand Islands National Wildlife Refuge were surveyed for sea turtle nesting activity from 1991-95. Raccoons depredated 76-100% of nests on Panther Key from 1991-94, until 14 raccoons were removed in 1995 resulting in 0% depredation and 2 more were removed in 1996 resulting in 0% depredation. Raccoon removal may be an effective management option for increasing sea turtle nest survival on barrier islands.

Southeastern Naturalist↗

USGS1999

Effects of egg and hatchling harvest on American alligators in Florida

Harvest of crocodilian eggs and young for captive rearing (ranching) has been used worldwide as an option for producing crocodilian skins and meat from wild stock. The long-term effects of harvesting a certain proportion of early age class, wild American alligators (Alligator mississippiensis) without repatriation is unknown. We removed an estimated 50% of annual production of alligators on Lakes Griffin and Jesup in central Florida over an 11-year period and monitored population levels via night-light counts. Densities of the total alligator population increased (P < 0.037) on all areas. Count densities of adult (≥183 cm total length [TL]) alligators increased (P < 0.003) on harvest areas but remained stable (P = 0.830) on the control (no harvest) area, Lake Woodruff National Wildlife Refuge (Lake Woodruff NWR). Observed densities of juvenile (<122 cm TL) alligators remained stable (P > 0.117), and subadult (122-182 cm TL) alligators increased (P < 0.011) on harvest areas. The density of juveniles on the control area increased (P = 0.006), and the density of subadults showed some evidence of increasing (P = 0.088). No changes were detected in size distributions on the treatment areas. Nest production, as observed from aerial helicopter surveys, increased (P < 0.039) on Lake Woodruff NWR and Lake Jesup and showed some evidence of an increase on Lake Griffin (P = 0.098) during 1983-91. A 50% harvest rate of eggs or hatchlings did not adversely affect recruitment into the subadult or adult size classes.

Journal of Wildlife Management↗

USGS1998

Size-sex variation in survival rates and abundance of pig frogs, Rana grylio, in northern Florida wetlands

During 1991-1993, we conducted capture-recapture studies on pig frogs, Rana grylio, in seven study locations in northcentral Florida. Resulting data were used to test hypotheses about variation in survival probability over different size-sex classes of pig frogs. We developed multistate capture-recapture models for the resulting data and used them to estimate survival rates and frog abundance. Tests provided strong evidence of survival differences among size-sex classes, with adult females showing the highest survival probabilities. Adult males and juvenile frogs had lower survival rates that were similar to each other. Adult females were more abundant than adult males in most locations at most sampling occasions. We recommended probabilistic capture-recapture models in general, and multistate models in particular, for robust estimation of demographic parameters in amphibian populations.

Journal of Herpetology↗

USGS1984

Observer visitation frequency and success of mourning dove nests: A field experiment

Field studies of nesting success generally require visits by the investigator to the nests under study. Such visits may themselves influence nesting success, however, and this possibility has been discussed and investigated by a number of workers with a variety of bird species. Livezey (1980) reviewed the relevant literature for duck nests and noted that most studies failed to demonstrate differences in nesting success between visited nests and those not visited. Livezey (1980) found in his own work that nest abandonment may have occurred as a result of disturbance by observers but that nest predation was not related to time spent by observers at nests or number of observers approaching nests. Various components of nesting and breeding success in seabirds are thought to be adversely affected by human disturbance and nest visitation (Gillett et al. 1975, Robert and Ralph 1975, Ollason and Dunnet 1980). Upland, ground-nesting species have also been studied (e.g. Stoddard 1931, Evans and Wolfe 1967, Henry 1969, Roseberry and Klimstra 1970, Klimstra and Roseberry 1975), and, although conclusions have varied, a number of these workers found no effect of observers on nest-predation rates.

The Auk↗

USGS1982

Mourning Dove Nesting: Seasonal Patterns and Effects of September Hunting

A nationwide State/Federal cooperative study was initiated in 1978 to examine effects of September hunting on mourning dove (Zenaida macroura) nesting. This study was designed to (1) determine the proportion of the annual total of dove nesting activity and production that occurs in September and October, and (2) determine if survival rates of mourning dove eggs and nestlings are lower in areas where early September dove hunting is permitted compared to areas where it is prohibited. During 1979 and 1980, 6,950 active nests were followed to obtain data on nesting patterns. Nest initiation was estimated both by backdating from hatch dates and by the numbers of nests found for the first time. The nationwide percent of the annual total of nests that were initiated in September and October was 1.0% based on backdating hatch dates and 2.7% based on nests found for the first time. Nesting activity was measured by numbers of eggs and nestlings present in weekly counts. Nationally, 4.5% of the annual total of nesting activity occurred in September and October. The observed period when 80% of the nests were active, based on hatch dates, lasted from April 22 to September 4. The measure of production used in this study was numbers of young fledged. Nationally, 10.3% of all observed fledging occurred in September and October. A decline in nests found in the latter half of the nesting season preceded the September 1 start of hunting. From this we concluded that the reduction in nesting activity at the end of the season is a natural phenomenon and not caused by hunting disturbance. In a separate part of this study, we estimated survival rates in hunted and nonhunted sections from data on 668 nests. The estimated daily survival rates for individual eggs and nestlings were 95.8% in the nonhunted and 95.0% in the hunted sections; the corresponding fledging rates were 33% and 26%, respectively. The fledging rates are lower because they are the daily survival rates operating over a 26-day nesting period. Neither differences in survival nor fledging rates between nonhunted and hunted sections were found to be statistically significant (p> 0.05). We determined that the statistical test was powerful enough to detect a reduction due to hunting from a hypothetical 96.0% to 94.2% in daily nestling survival rates (from 35% to 21% fledging rates) with 80% probability. An undetected reduction in fledging rate of that magnitude would probably reduce the overall fledging rate by less than 1 percentage point, because only a small proportion of the nesting doves is exposed to hunting for the full 26 day nesting cycle. In conclusion, we found that only a small proportion of total annual nesting attempts was exposed to hunting. There was no statistically significant difference in survival rates in sections where hunting was permitted compared to sections where it was prohibited. We concluded from this study that dove hunting under current regulations has no substantial effect on recruitment of fledglings into the mourning dove population.

Book↗

USGS1981

Importance of structural stability to success of mourning dove nests

Studies of nest-site selection and nesting habitats often involve a "characterization" of nests and of habitats in which nests are found. Our objective in the present work is to identify nest-site characteristics that are associated with variation in components of Mourning Dove ( Zenaida macroura ) fitness (e.g. the probability of a nest succeeding), as opposed to simply "characterizing" dove nest sites. If certain nest- site characteristics affect the probability that a nest will succeed, then we suspect that these characteristics will be associated with either concealment (the probability of detection by certain predators) or structural stability (the probability of eggs or entire nests falling to the ground as a result of wind, rain storms, parental activity, etc.). Although other workers agree that structural stability is an important determinant of Mourning Dove nesting success (e.g. McClure 1944: 384; Woolfenden and Rohwer 1969: 59), we are aware of no actual tests of this hypothesis.

The Auk↗