scholarly journals Detection of Gopher Tortoise Burrows Before and After a Prescribed Fire: Implications for Surveys

2018 ◽  
Vol 10 (1) ◽  
pp. 62-68 ◽  
Author(s):  
Jennifer M. Howze ◽  
Lora L. Smith
Keyword(s):  
Habitat Structure ◽  
Survey Methodology ◽  
Distance Sampling ◽  
Population Estimates ◽  
Line Transect ◽  
Past Century ◽  
Prescribed Burn ◽  
Gopher Tortoise ◽  
Imperfect Detection ◽  
Abundance Estimate

Abstract Gopher tortoise Gopherus polyphemus populations have declined by as much as 80% over the past century, primarily as a result of habitat loss. In 2006, the eastern population of the gopher tortoise was petitioned for federal listing as threatened. In response, a Candidate Conservation Agreement was developed for the gopher tortoise. A Candidate Conservation Agreement is a voluntary agreement between the U.S. Fish and Wildlife Service and other interested parties to address the conservation needs of a species before it becomes federally listed and to enact measures to preclude the need to list the species. The gopher tortoise Candidate Conservation Agreement identified an assessment of the status of populations on protected lands as a priority and line transect distance sampling (LTDS) was adopted as the standardized survey methodology. Surveys with LTDS rely on detection of gopher tortoise burrows because tortoises are fossorial. However, gopher tortoise burrows vary greatly in size and small burrows of juveniles are rarely detected. Although LTDS is statistically robust and allows for imperfect detection, few studies have examined how detection varies with tortoise burrow size and whether habitat structure may influence detection of gopher tortoise burrows. Both factors could affect the accuracy of population estimates using LTDS and interpretation of demographic parameters needed for the Candidate Conservation Agreement. Therefore, we conducted surveys for burrows using LTDS before (28 March–13 April 2016) and after (9–18 May 2016) a prescribed burn, which reduced vegetation cover. We detected significantly more burrows (P < 0.001, n = 651) of all sizes after the burn, and the burrow abundance estimate was 64% higher postburn. Our study showed that conducting gopher tortoise surveys after a prescribed burn increased detections and provided a more accurate population estimate. We therefore recommend conducting surveys immediately after a burn. However, varying burn cycles on large sites may make it difficult to survey following a prescribed burn and because the effects of a burn on habitat structure may vary within a site, methods to account for variation in detection due to habitat structure are needed. Population estimates for gopher tortoises using LTDS that do not account for variation in detection due to habitat structure likely underestimate population size.

A comparison of line-transect distance sampling methods for estimating gopher tortoise population densities

2015 ◽  
Vol 39 (4) ◽  
pp. 804-812 ◽  
Author(s):  
Traci D. Castellón ◽  
Betsie B. Rothermel ◽  
Saif Z. Nomani
Keyword(s):  
Sampling Methods ◽  
Distance Sampling ◽  
Line Transect ◽  
Population Densities ◽  
Gopher Tortoise

Application of distance sampling to estimate population densities of large herbivores in Kruger National Park

2008 ◽  
Vol 35 (4) ◽  
pp. 371 ◽  
Author(s):  
J. M. Kruger ◽  
B. K. Reilly ◽  
I. J. Whyte
Keyword(s):  
National Park ◽  
Distance Sampling ◽  
Kruger National Park ◽  
Population Trends ◽  
Population Estimates ◽  
Line Transect ◽  
Large Herbivores ◽  
Sampling Intensity ◽  
Coefficients Of Variation ◽  
White Rhinoceros

Aerial surveys have been used in the Kruger National Park, South Africa, to count large ungulates since the late 1970s. After 1998, aerial line-transect sampling using fixed-wing aircraft and Distance analyses replaced the ‘total’ counting method. This paper investigates these methods and three sampling intensities for estimating the densities of nine large ungulate species in Kruger National Park. Estimates suitable for the detection of population trends and making management decisions were decided by examination of coefficients of variation (set <20%, a priori). Despite the likely violation of some key assumptions of Distance sampling methods, analyses gave population estimates with adequate coefficients of variation for monitoring trends in impala, giraffe, zebra, kudu, white rhinoceros, and elephant bull populations. Significant improvements in precision were obtained at higher sampling intensities for kudu, giraffe, bull elephants and white rhinoceros, but these species already had sufficiently precise population estimates for the detection of trends at the lowest sampling intensity (15%). The estimates for warthog, wildebeest and waterbuck populations were, however, insufficiently precise for assessing population trends. Increasing sampling intensity to 22% and higher did not significantly increase the precision of the Distance estimates for these species. Shortcomings in interpretation of the data caused by violations of critical assumptions of analyses are identified and discussed.

Population Estimates of Hubbard’s Sportive Lemur (Lepilemur hubbardorum) at Zombitse-Vohibasia National Park, Madagascar

2021 ◽  
pp. 1-9
Author(s):  
Luke D. Martin ◽  
Amanda K. Rowe ◽  
Eva S. Nomenjanahary ◽  
Serenity K. Montaño ◽  
Patricia C. Wright ◽  
...  
Keyword(s):  
National Park ◽  
Primate Species ◽  
Population Estimates ◽  
Conservation Priorities ◽  
Line Transect ◽  
Population Declines ◽  
Sampling Area ◽  
Abundance Estimate ◽  
Protected Forests ◽  
Sportive Lemur

Estimates of population size are fundamental to setting conservation priorities for threatened primate species. Many taxa in the lemur genus <i>Lepilemur</i> remain understudied, and basic population statistics are often dated, incomplete, or absent. Hubbard’s sportive lemur (<i>Lepilemur hubbardorum</i>) is known only from the Zombitse-Vohibasia National Park region in southwestern Madagascar. It is listed as Endangered by the IUCN owing to its fragmented, declining habitat and limited geographic range. However, this classification has not been confirmed through systematic population estimates. To address this issue, we undertook line transect surveys in the Zombitse parcel of the National Park. We applied geospatial analyses and data to quantify forest area as a proxy for <i>L</i>. <i>hubbardorum</i>habitat. We recorded a total of 234 <i>L</i>.<i> hubbardorum</i> sightings over 18 survey nights, representing 47.2 km of survey effort. Our surveys revealed population densities of 145.6 <i>L</i>.<i> hubbardorum</i> individuals per km<sup>2</sup> (95% CI: 97.2–218.1), for an extrapolated abundance estimate of ca. 16,500–18,000 <i>L</i>. <i>hubbardorum</i> individuals across the protected forests of the Zombitse parcel. This abundance estimate should be considered provisional, however, because our restricted sampling area did not include the more remote regions of the National Park where habitat disturbance and hunting practices have likely contributed to localized population declines.

scholarly journals Added Value: Gopher Tortoise Surveys Provide Estimates of Gopher Frog Abundance in Tortoise Burrows

2020 ◽  
Author(s):  
Lora L Smith ◽  
Jennifer M. Howze ◽  
Jennifer S. Staiger ◽  
Eric R. Sievers ◽  
Deborah Burr ◽  
...  
Keyword(s):  
Environmental Variability ◽  
Distance Sampling ◽  
Added Value ◽  
Line Transect ◽  
Gopher Tortoise ◽  
Gopherus Polyphemus ◽  
Abundance Estimates ◽  
Mean Width ◽  
The Status ◽  
Terrestrial Life

The gopher frog Lithobates capito is one of the most terrestrial frogs in the southeastern U.S. and often inhabits gopher tortoise burrows Gopherus polyphemus outside of the breeding season. Gopher frog populations have declined, and the species is under review for listing as threatened or endangered under the U.S. Endangered Species Act. Much of our knowledge on the status of gopher frogs is based on detections of larvae at breeding wetlands, which can be challenging due to environmental variability and provides no information on the terrestrial life stages of the species. Therefore, an alternative method is called for. We recorded observations of gopher frogs during gopher tortoise surveys at four conservation lands in Florida and used line transect distance sampling to estimate frog abundance. We also recorded burrow size, incidence of frog co-occupancy with tortoises, and distance from frog-occupied burrows to breeding wetlands. We observed 274 gopher frogs in 1,097 tortoise burrows at the four sites. The proportion of burrows occupied by gopher frogs among sites ranged from 0.17 to 0.25. Gopher frog abundance in tortoise burrows was 742 (512–1,076 95% CL) at Etoniah Creek State Forest, 465 (352–615) at Ft. White Wildlife Environmental Area, 411(283–595) at Mike Roess Gold Head Branch State Park, and 134 (97–186) at Watermelon Pond Wildlife Environmental Area. We observed up to four frogs in a single burrow. The proportion of frogs detected in burrows occupied by a gopher tortoise ranged from 0.46 to 0.79 among sites, and overall, gopher frogs preferred burrows occupied by tortoises over unoccupied burrows (χ 2 = 15.875, df=3, p = 0.001). Gopher frogs used burrows from 7 to 43 cm in width; mean width of frog-occupied burrows did not differ from that of unoccupied burrows ( F 1,3 = 0.0492, p = 0.8245). Distance from frog-occupied tortoise burrows to the nearest breeding wetland ranged from 141 to 3,402 m. Our data on gopher frogs collected in conjunction with gopher tortoise monitoring efforts using line transect distance sampling and burrow cameras provided novel information on frog abundance in their terrestrial habitat and required no additional effort. However, the extent to which frogs use tortoise burrows relative to other available refuges (small mammal burrows, stumps, or other structures) is unknown, thus our estimates should be considered conservative. We suggest that terrestrial abundance estimates for gopher frogs can complement efforts to monitor breeding activity to provide a more comprehensive means of monitoring population trends in this cryptic species.

scholarly journals Techniques for Estimating the Size of Low-Density Gopher Tortoise Populations

2017 ◽  
Vol 8 (2) ◽  
pp. 377-386 ◽  
Author(s):  
Jonathan M. Stober ◽  
Rocio Prieto-Gonzalez ◽  
Lora L. Smith ◽  
Tiago A. Marques ◽  
Len Thomas
Keyword(s):  
Habitat Management ◽  
Distance Sampling ◽  
Probability Of Detection ◽  
Line Transect ◽  
Efficient Design ◽  
Gopher Tortoise ◽  
Gopherus Polyphemus ◽  
Line Transect Survey ◽  
Estimate Population Size ◽  
Survey Designs

Abstract Gopher tortoises (Gopherus polyphemus) are candidates for range-wide listing as threatened under the U.S. Endangered Species Act. Reliable population estimates are important to inform policy and management for recovery of the species. Line transect distance sampling has been adopted as the preferred method to estimate population size. However, when tortoise density is low, it can be challenging to obtain enough tortoise observations to reliably estimate the probability of detection, a vital component of the method. We suggest a modification to the method based on counting usable tortoise burrows (more abundant than tortoises) and separately accounting for the proportion of burrows occupied by tortoises. The increased sample size of burrows can outweigh the additional uncertainty induced by the need to account for the proportion of burrows occupied. We demonstrate the method using surveys conducted within a 13,118-ha portion of the Gopher Tortoise Habitat Management Unit at Fort Gordon Army Installation, Georgia. We used a systematic random design to obtain more precise estimates, using a newly developed systematic variance estimator. Individual transects had a spatially efficient design (pseudocircuits), which greatly improved sampling efficiency on this large site. Estimated burrow density was 0.091 ± 0.011 burrows/ha (CV = 12.6%, 95% CI = 0.071–0.116), with 25% of burrows occupied by a tortoise (CV = 14.4%), yielding a tortoise density of 0.023 ± 0.004 tortoise/ha (CV = 19.0%, 95% CI = 0.016–0.033) and a population estimate of 297 tortoises (95% CI = 210–433). These techniques are applicable to other studies and species. Surveying burrows or nests, rather than animals, can produce more reliable estimates when it leads to a significantly larger sample of detections and when the occupancy status can reliably be ascertained. Systematic line transect survey designs give better precision and are practical to implement and analyze.

scholarly journals Population estimates of Endangered Mongolian saiga Saiga tatarica mongolica: implications for effective monitoring and population recovery

Oryx ◽  
2010 ◽  
Vol 44 (2) ◽  
pp. 285-292 ◽  
Author(s):  
Julie K. Young ◽  
Kim M. Murray ◽  
Samantha Strindberg ◽  
Bayarbaatar Buuveibaatar ◽  
Joel Berger
Keyword(s):  
Distance Sampling ◽  
Iucn Red List ◽  
Population Trends ◽  
Population Estimates ◽  
Line Transect ◽  
Population Recovery ◽  
Saiga Tatarica ◽  
Survey Protocol ◽  
Global Population

AbstractThe global population of saiga Saiga tatarica, categorized as Critically Endangered on the IUCN Red List, declined by > 95% at the end of the 20th century, resulting in several conservation initiatives to protect the species. Previously used methods to monitor population trends were inadequate to assess numbers of saiga properly. We report findings from the first survey for Mongolian saiga S. tatarica mongolica to utilize statistically rigorous methodology, using line transect distance sampling in 2006 and 2007 to obtain population estimates in and around the Sharga Nature Reserve, the southern part of the species' current range. We estimate a density of 0.54 and 0.78 saiga km-2 in 2006 and 2007, respectively. Our best models suggest that 4,938 (95% confidence interval, CI = 2,762–8,828) saiga occupied the 4,524-km2 study area in 2006 and 7,221 (95% CI = 4,380–11,903) occupied the 4,678-km2 study area in 2007. Although these estimates, with their large confidence intervals, preclude an assessment of the impacts of conservation initiatives on population trends, they suggest that the Mongolian saiga population is larger than previous reports based on minimum counts, and adequate to support in situ population recovery. Modifications to the survey protocol hold promise for improving the precision of future estimates. Distance sampling may be a useful, scientifically defensible method for monitoring saiga population trends and assessing the effectiveness of conservation efforts to stabilize and recover populations.

scholarly journals Measuring Indian Blackbuck Antilope cervicapra (Mammalia: Cetartiodactyla: Bovidae) abundance at Basur Amruth Mahal Kaval Conservation Reserve, Chikkamagaluru, southern India

2017 ◽  
Vol 9 (7) ◽  
pp. 10468
Author(s):  
H.S. Sathya Chandra Sagar ◽  
P. U. Antoney
Keyword(s):  
Detection Probability ◽  
Critical Role ◽  
Distance Sampling ◽  
Southern India ◽  
Imperfect Detection ◽  
Abundance Estimate ◽  
Grassland Ecosystems ◽  
Periodic Monitoring ◽  
The Tropics ◽  
Antilope Cervicapra

Grasslands are among the most critically endangered ecosystems in the tropics, but they are often treated as wastelands and conservation efforts are seldom directed towards these landscapes.  The Blackbuck Antilope cervicapra is a large wild herbivore found in most grassland ecosystems across India.  Despite their critical role in their trophic web, there are no reliable estimates of Blackbuck populations from their geographic range that takes detection probability into consideration.  In this study, we conducted field surveys to estimate Blackbuck density in Basur Amruth Mahal Kaval Conservation (BAMKCR) with an area of 7.36km2 in southern India.  We surveyed Blackbucks for a week in July 2014 along straight line transects between 09:00–12:00 hr and used the distance sampling approach to address the imperfect detection.  A total of three transect lines of lengths 3.01km, 2.4km and 1.2km were sampled for seven temporal replicates.  With an effort of 46.27km, 56 sightings of Blackbucks were recorded that was analyzed using the program DISTANCE.  With a detection probability of 0.58 (0.053 SD) the estimated density of Blackbuck was 26.23 (6 SD) individuals/km2.  The derived abundance estimate was 193 (c. 148–238) individuals in the study area.  Our results show implications of a statistically robust design that accounts for imperfect detection.  It provides an insight into a resident population of Blackbucks in a dynamic and fragile habitat.  Blackbuck density estimate from this study sets the background for periodic monitoring of their populations, examination of the impacts of habitat modifications and gauge long-term viability of the grassland habitat in BAMKCR.

scholarly journals Population estimates of Antillean manatees in Puerto Rico: an analytical framework for aerial surveys using multi-pass removal sampling

2019 ◽  
Vol 100 (4) ◽  
pp. 1340-1349
Author(s):  
Jaime A Collazo ◽  
Matthew J Krachey ◽  
Kenneth H Pollock ◽  
Francisco J Pérez-Aguilo ◽  
Jan P Zegarra ◽  
...  
Keyword(s):  
Puerto Rico ◽  
Detection Probability ◽  
Analytical Framework ◽  
Population Estimates ◽  
High Concentration ◽  
Imperfect Detection ◽  
Factors Affecting ◽  
Management Actions ◽  
Aerial Surveys ◽  
Population Size Estimates

AbstractEffective management of the threatened Antillean manatee (Trichechus manatus manatus) in Puerto Rico requires reliable estimates of population size. Estimates are needed to assess population responses to management actions, and whether recovery objectives have been met. Aerial surveys have been conducted since 1976, but none adjusted for imperfect detection. We summarize surveys since 1976, report on current distribution, and provide population estimates after accounting for apparent detection probability for surveys between June 2010 and March 2014. Estimates in areas of high concentration (hotspots) averaged 317 ± 101, three times higher than unadjusted counts (104 ± 0.56). Adjusted estimates in three areas outside hotspots also differed markedly from counts (75 ± 9.89 versus 19.5 ± 3.5). Average minimum island-wide estimate was 386 ± 89, similar to the maximum estimate of 360 suggested in 2005, but fewer than the 700 recently suggested by the Puerto Rico Manatee Conservation Center. Manatees were more widespread than previously understood. Improving estimates, locally or island-wide, will require stratifying the island differently and greater knowledge about factors affecting detection probability. Sharing our protocol with partners in nearby islands (e.g., Cuba, Jamaica, Hispaniola), whose populations share genetic make-up, would contribute to enhanced regional conservation through better population estimates and tracking range expansion.El manejo efectivo del manatí antillano amenazado en Puerto Rico requiere estimados de tamaños de poblaciónes confiables. Dichas estimaciones poblacionales son necesarias para evaluar las respuestas a las acciones de manejo, y para determinar si los objetivos de recuperación han sido alcanzados. Se han realizado censos aéreos desde 1976, pero ninguno de ellos han sido ajustados para detecciones imperfectas. Aquí resumimos los censos desde 1976, actualizamos la distribución, y reportamos los primeros estimados poblacionales ajustados para la probabilidad de detección aparente en los censos de Junio 2010 a Marzo 2014. Las estimaciones poblacionales en áreas de mayor concentración del manatí promedió 317 ± 103, tres veces más abundante que los conteos sin ajuste (104 ± 0.56). Las estimaciones poblacionales en tres áreas fuera de las áreas de mayor concentración del manatí también fueron marcadamente diferentes (75 ± 9.89 vs 19.5 ± 3.5). El estimado mínimo poblacional en la isla entera fue de 386 ± 89, similar al estimado máximo de 360 sugerido en el año 2005, pero menor a los 700 sugeridos recientemente por el Centro de Conservación de Manatíes de Puerto Rico. Documentamos que el manatí tiene una distribución más amplia de lo que se sabía con anterioridad. El mejoramiento de los estimados poblacionales locales o a nivel de isla requerirá que se estratifique a la isla en forma diferente y que se investiguen los factores que influencian a la probabilidad de detección. Compartir protocolos como este con colaboradores de islas vecinas (por. ej., Cuba, Jamaica, Española), cuyas poblaciones de manatíes comparten material genético, contribuiría a la conservación regional mediante mejores estimaciones poblacionales y monitoreo de la expansión de su ámbito doméstico.

scholarly journals Getting the Most From Surveys: How Method Selection and Method Modification Impact Butterfly Survey Data

2021 ◽  
Author(s):  
Katherine C Kral-O’Brien ◽  
Adrienne K Antonsen ◽  
Torre J Hovick ◽  
Ryan F Limb ◽  
Jason P Harmon
Keyword(s):  
Species Richness ◽  
New Species ◽  
Count Data ◽  
Distance Sampling ◽  
Line Transect ◽  
Similar Species ◽  
Method Selection ◽  
M 10 ◽  
Sampling Procedures

Abstract Many methods are used to survey butterfly populations, with line transect and area surveys being prominent. Observers are typically limited to search within 5 or 10 m from the line, while observers are unrestricted in larger specified search regions in area surveys. Although methods differ slightly, the selection is often based on producing defendable data for conservation, maximizing data quality, and minimizing effort. To guide method selection, we compared butterfly surveys using 1) line versus area methods and 2) varying width transects (5 m, 10 m, or unrestricted) using count data from surveys in North Dakota from 2015 to 2018. Between line and area surveys, we detected more individuals with area surveys, even when accounting for effort. However, both methods accumulated new species at similar rates. When comparing transect methodology, we detected nearly 60% more individuals and nine more species when transect width increased from 5 m to unrestricted, despite similar effort across methodology. Overall, we found line surveys slightly less efficient at detecting individuals, but they collected similar species richness to area surveys when accounting for effort. Additionally, line surveys allow the use of unrestricted-width transects with distance sampling procedures, which were more effective at detecting species and individuals while providing a means to correct count data over the same transect length. Methods that reduce effort and accurately depict communities are especially important for conservation when long-term datasets are unavailable.

Harbor porpoise (Phocoena phocoena) recovery in the inland waters of Washington: estimates of density and abundance from aerial surveys, 2013–2015

2016 ◽  
Vol 94 (7) ◽  
pp. 505-515 ◽  
Author(s):  
Thomas A. Jefferson ◽  
Mari A. Smultea ◽  
Sarah S. Courbis ◽  
Gregory S. Campbell
Keyword(s):  
Puget Sound ◽  
Distance Sampling ◽  
Line Transect ◽  
Inland Waters ◽  
San Juan ◽  
Phocoena Phocoena ◽  
Harbor Porpoise ◽  
San Juan Islands ◽  
Juan De Fuca ◽  
Harbor Porpoises

The harbor porpoise (Phocoena phocoena (L., 1758)) used to be common in Puget Sound, Washington, but virtually disappeared from these waters by the 1970s. We conducted systematic aerial line-transect surveys (17 237 km total effort) for harbor porpoises, with the goal of estimating density and abundance in the inland waters of Washington State. Surveys in Puget Sound occurred throughout the year from 2013 to 2015, and in the Strait of Juan de Fuca and the San Juan Islands (and some adjacent Canadian waters) in April 2015. We used a high-wing, twin-engine Partenavia airplane and four observers (one on each side of the plane, one looking through a belly port, and one recording data). A total of 1063 harbor porpoise groups were sighted. Density and abundance were estimated using conventional distance sampling methods. Analyses were limited to 447 harbor porpoise groups observed during 5708 km of effort during good sighting conditions suitable for line-transect analysis. Harbor porpoises occurred in all regions of the study area, with highest densities around the San Juan Islands and in northern Puget Sound. Overall, estimated abundance for the Washington Inland Waters stock was 11 233 porpoises (CV = 37%, 95% CI = 9 616 – 13 120). This project clearly demonstrated that harbor porpoises have reoccupied waters of Puget Sound and are present there in all seasons. However, the specific reasons for their initial decline and subsequent recovery remain uncertain.

Sign in / Sign up

Export Citation Format

Share Document