H. Franklin Percival

An Assessment of Small Unmanned Aerial Vehicles for Wildlife Research

Abstract Aerial surveys are valuable tools for wildlife research and management. However, problems with safety, cost, statistical integrity, and logistics continue to impede aerial surveys from manned aircraft. The use of small, unmanned aerial vehicles (UAVs) may offer promise for addressing these problems and become a useful tool for many wildlife applications, such as for collecting low-altitude aerial imagery. During 2002 and 2003, we used a 1.5-m wingspan UAV equipped with autonomous control and sophisticated video equipment to test the potential usefulness of such an aircraft for wildlife research applications in Florida, USA. The UAV we used completed >30 missions (missions averaging 13 km linear distance covered) over 2 years before finally crashing due to engine failure. The UAV captured high-quality, progressive-scan video of a number of landscapes and wildlife species (white ibis [Eudocimus albus], other white wading birds, American alligator [Alligator mississippiensis], and Florida manatee [Trichechus manatus]). The UAV system was unable to collect georeferenced imagery and was difficult to deploy in unimproved areas. The performance of the autonomous control system and the quality of the progressive-scan imagery indicated strong promise for future UAVs as useful field tools. For small UAVs to be useful as management or research tools, they should be durable, modular, electric powered, launchable and recoverable in rugged terrain, autonomously controllable, operable with minimal training, and collect georeferenced imagery.

Ecological effects of coastal marsh impoundments: a review

Many coastal resource managers believe estuarine marshes are critically important to estuarine fish and shellfish, not only because of the habitat present for juvenile stages, but also because of the export of detritus and plant nutrients that are consumed in the estuary. Concern has been widely expressed that diking and flooding marshes (impounding) for mosquito control and waterfowl management interferes with these values of marshes. Major changes caused by impoundment include an increase in water level, a decrease in salinity, and a decrease in the exchange of marsh water with estuarine water. Alteration of species composition is dramatic after impoundment. Changes in overall production and transport phenomena, however—and the consequences of these changes— may not be as great in some cases as the concern about these has implied. Although few data are available, a more important concern may be the reduction of access by estuarine fish and shellfish to the abundant foods and cover available in many natural, as well as impounded, marshes. Perhaps even more important is the occasional removal of free access to open water when conditions become unfavorable in impounded marsh that is periodically opened and closed. Collection of comparative data on the estuarine animal use of various configurations of natural and impounded marshes by estuarine animals should lead to improved management of both impounded and unimpounded marshes.

Estimating Distribution of Hidden Objects with Drones: From Tennis Balls to Manatees

Unmanned aerial vehicles (UAV), or drones, have been used widely in military applications, but more recently civilian applications have emerged (e.g., wildlife population monitoring, traffic monitoring, law enforcement, oil and gas pipeline threat detection). UAV can have several advantages over manned aircraft for wildlife surveys, including reduced ecological footprint, increased safety, and the ability to collect high-resolution geo-referenced imagery that can document the presence of species without the use of a human observer. We illustrate how geo-referenced data collected with UAV technology in combination with recently developed statistical models can improve our ability to estimate the distribution of organisms. To demonstrate the efficacy of this methodology, we conducted an experiment in which tennis balls were used as surrogates of organisms to be surveyed. We used a UAV to collect images of an experimental field with a known number of tennis balls, each of which had a certain probability of being hidden. We then applied spatially explicit occupancy models to estimate the number of balls and created precise distribution maps. We conducted three consecutive surveys over the experimental field and estimated the total number of balls to be 328 (95%CI: 312, 348). The true number was 329 balls, but simple counts based on the UAV pictures would have led to a total maximum count of 284. The distribution of the balls in the field followed a simulated environmental gradient. We also were able to accurately estimate the relationship between the gradient and the distribution of balls. Our experiment demonstrates how this technology can be used to create precise distribution maps in which discrete regions of the study area are assigned a probability of presence of an object. Finally, we discuss the applicability and relevance of this experimental study to the case study of Florida manatee distribution at power plants.

Nest-site selection by the loggerhead sea turtle in Florida's Ten Thousand Islands

Loggerhead sea turtles (Caretta caretta) nest in numerous substrate and beach types within the Ten Thousand Islands (TTI) of southwest Florida. Nest-site selection was analyzed on 12 islands within this archipelago. Physical characteristics of beaches were recorded to identify the relatedness of these var- iables and to determine their importance for nest-site selection in C. caretta. These characteristics included ordinal aspect, beach length, height of canopy, beach width, overall slope (beach slope and slope of offshore approach), and sand samples analyzed for pH, water content, organic content, shelliness (% of calcium car- bonate content), and particle size (8 size classes). All physical variables, as well as nesting densities and locations, were included in a tree regression model to examine nest-site selection. In the TTI, loggerheads use wide beaches (>8.5 m) that inherently have less slope and, secondarily, wide beaches that have less shells (low amounts of calcium carbonate; >8.5 m) in the nesting substrate. In addition, C. caretta nest sites were located within or in close proximity to the supra-littoral vegetation zone of beaches in the TTI.

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.

MOVEMENTS OF FLORIDA APPLE SNAILS IN RELATION TO WATER LEVELS AND DRYING EVENTS

Florida apple snails (Pomacea paludosa) apparently have only a limited tolerance to wetland drying events (although little direct evidence exists), but their populations routinely face dry downs under natural and managed water regimes. In this paper, we address speculation that apple snails respond to decreasing water levels and potential drying events by moving toward refugia that remain inundated. We monitored the movements of apple snails in central Florida, USA during drying events at the Blue Cypress Marsh (BC) and at Lake Kissimmee (LK). We monitored the weekly movements of 47 BC snails and 31 LK snails using radio-telemetry. Snails tended to stop moving when water depths were <10 cm; however, there was no apparent effect of water depth on distance traveled in water depths >10 cm. Snails moved along the greatest positive depth gradient (i.e., towards deeper water) when they encountered water depths between 10 and 20 cm. Snails tended to move toward shallower water in water depths ≥50 cm, suggesting that snails were avoiding deep water areas such as canals and sloughs. Of the 11 BC snails originally located in the area that eventually went dry, three (27%) were found in deep water refugia by the end of the study. Only one of the 31 LK snails escaped the drying event by moving to deeper water. Our results indicate that some snails may opportunistically escape drying events through movement. The tendency to move toward deeper water was statistically significant and indicates that this behavioral trait might enhance survival when the spatial extent of a dry down is limited. However, as water level falls below 10 cm, snails stop moving and become stranded. As the spatial extent of a dry down increases, we predict that the number of snails stranded would increase proportionally. Stranded Pomacea paludosa must contend with dry marsh conditions, possibly by aestivation. Little more than anecdotal information has been published on P. paludosa aestivation, but it is a common adaptation among other apple snails (Caenogastropoda: Ampullaridae).

Use of Unmanned Aircraft Systems to Delineate Fine-Scale Wetland Vegetation Communities

Remote sensing of wetlands has primarily focused on delineating wetlands within a non-wetland matrix. However, within-wetland changes are arguably just as important as loss of wetland area, particularly in a time of accelerated climate change. Remote sensing is a critical source of data for ecological models that explain and predict landscape changes, but data specifications, including spatial and temporal resolution, must be appropriate for applications. Unmanned Aircraft Systems (UASs) can be used to collect fine spatial resolution data with a temporal resolution more tailored to application need, instead of satellite orbital times or flight schedules. We used data collected from an UAS to acquire true color data within a wetland landscape and tested our ability to automatically classify plant communities from fine-resolution data. Classification accuracies were low for certain classes when nine vegetation communities were mapped, but the overall accuracy was on par with other remote sensing analyses. We demonstrate that classification data derived from UAS fine-resolution imagery is reasonably accurate and discuss the benefits and challenges of using UAS for wetland mapping.

Modeling the Effect of Toe Clipping on Treefrog Survival: Beyond the Return Rate

Abstract 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.

Raccoon Removal Reduces Sea Turtle Nest Depredation in the Ten Thousand Islands of Florida

Abstract 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.

COLLECTING FLORIDA APPLESNAILS (POMACEA PALUDOSA) FROM WETLAND HABITATS USING FUNNEL TRAPS

Traditional methods for sampling aquatic macro-invertebrates are very labor-intensive and largely ineffective when attempting to collect Florida applesnails (Pomacea paludosa) from their natural wetland habitats. We found the use of funnel traps an effective alternative that decreased collection time ten-fold and required considerably less labor than throw traps. The funnel traps described herein can be used effectively for collecting applesnails in a variety of wetland habitat types and plant densities, and they may also be effective in catching other wetland organisms (e.g., Kinosternid turtles).