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Predator Project Accomplishments

Developing Control Methods, Evaluating Impacts, and Applying Ecology, Behavior, Genetics, and Demographics to Manage Predators

PROJECT GOAL: Improve the current knowledge of predator ecology, behavior, genetics, and demographics relative to predators and depredation on species of human concern, assess predator responses to management strategies, and develop techniques and control methods to effectively assess and manage mammalian predation on livestock and natural resources.

Project Accomplishments 2010

The development of new predator management tools to reduce livestock losses and protect public safety is a high priority for APHIS Wildlife Services as managers and the livestock industry as producers. Livestock predation costs producers approximately $93 million each year. Concerns also exist for public safety and animal welfare when predators cause conflicts and management is implemented. The National Wildlife Research Center (NWRC) uses a multi-disciplinary approach to study interactions among predators and the impact of predators and predator removal on ecosystems and wildlife populations. Results from these studies are fundamental to selective and socially responsible predator management. In addition, NWRC researchers are developing improved methods for capturing predators; monitoring their behaviors and movements; developing more selective predacides; and finding alternative, nonlethal tools and techniques to prevent predatory behavior.

Coyote Sterilization To Reduce Predation on Pronghorns—Coyote predation accounts for the majority of neonatal pronghorn mortality in many areas and may influence local population declines. Current techniques used to manage coyote predation on wildlife species often focus on lethal control methods, especially where nonlethal methods are not effective. However, coyote sterilization has been shown to be effective in reducing sheep predation in certain situations. Sterilization reduces the energetic need for parents to provision coyote pups, which may decrease predation on fawns by sterile coyotes.

photo of pronghorn antelopeIn a recent study, NWRC and Utah State University researchers further examined the potential value of this management method. The researchers used tubal ligation and vasectomy to sterilize 15 coyotes while maintaining pair bonds and territoriality. Seven additional coyotes were captured and sham sterilized. They also monitored 71 pronghorn fawns by radio telemetry for 1 year pre-treatment and coyotes and pronghorn fawns for one year post-treatment. In addition, the researchers examined the effects of sterilization on coyote territorial maintenance and survival. The results showed that the survival of fawns was higher in home ranges of sterile coyotes than fawns in home ranges of non-sterilized coyotes. The results also supported the hypothesis that sterilization, while keeping hormonal systems intact, did not change coyote territorial behaviors. Packs of sterile coyotes were the same size as packs of non-sterilized coyotes, and sterile and non-sterile coyote packs maintained similar home range sizes in all seasons tested. Residency rates were also similar for all coyote packs.

Based on this research, coyote sterilization may prove useful as a possible tool to boost pronghorn fawn survival in areas where fawn survival is a critical factor in pronghorn population persistence and where lethal control is not a viable management option.

Effects of Maternal Nutrition on Whelping Rates in Coyotes—To determine if nutritional status during the postnatal period affected reproductive fitness in coyotes, scientists at the NWRC field station in Logan, UT, hand-reared 24 pups from 10 days to six months of age on either an unrestricted or reduced nutrient diet. Scientists assessed the pups' weight, stature, blood and hormone values, and reproductive performance during the first reproductive season. Pups on the unrestricted nutrient diet weighed more than those raised on the reduced nutrient diet. Of the 21 blood parameters analyzed, 19 differed in concentrations as the pups matured. The study results did not show relationships between diet and leptin or social rank and photo of coyote puptestosterone. Eighty-three percent of the females became pregnant, with 80% known to have produced viable young. Animals on the reduced nutrient diet produced nearly three times more pups than those on the unrestricted nutrient diet did. Scientists also noted a strong similarity in placental implantation rates among sibling sisters, which suggests that maternal effects may influence reproductive performance in juvenile coyotes.

These findings are useful in understanding time lags in coyote reproduction, which in turn influence depredation rates on domestic livestock.

Evaluation of Cable Foot Restraints—Negative public perceptions regarding the use of foot-hold traps have led to restrictions or all-out bans on these traps in several States. However, traps can be selective and effective tools for wildlife managers. To compensate for the loss of this tool, wildlife managers in some areas use cable foot-restraints to capture coyotes. In a continued effort to improve the selectivity of traps and the welfare of trapped animals, NWRC researchers evaluated animal injuries associated with three types of cable foot-restraints:

  • standard cable restrain—53.34 centimeters of 0.32-centimeter-diameter, 7 x 19-strand cable with a cam-lock;
  • sleeved cable restraint—same as standard, but with a 4.45-centimeter-long, 0.476-centimeter-diameter, clear plastic tube fitted over the cable; and
  • chain cable restraint—same as standard, but with 3.02 centimeters of a 0.2-centimeter-diameter, twist-link chain that attaches the lock to the cable.

During 2004 to 2006, NWRC researchers captured and examined 21, 14, and 17 coyotes using the standard, sleeved, and chain cables, respectively. The researchers used International Standardization for Organization (ISO) injury scores to evaluate the cables. There were no significant differences in injury scores between the standard restraint and the other two cable restraints. However, injury scores for coyotes captured in sleeved restraints were higher than those for coyotes captured in chain restraints. The sleeve may have prevented the cable from tightening snugly on the coyote's foot, allowing the leg to move against the lock and causing more lacerations, abrasions, and other injuries. The chain restraint had the lowest injury score. Researchers believe this could be the result of (1) the links within the chain providing a greater, rounded surface area, thus distributing the pressure of the device's grip; or (2) the lengths of chain acting similar to teeth or buttons on some jawed devices, which are thought to reduce movement and therefore reduce injury. All three restraints tested had lower injury scores than unpadded steel-jaw traps, but only the chain cable restraint had a lower mean injury score (though only slightly) than the padded steel-jaw trap. Scientists note that the padded foot-hold trap may cause less injury to captured coyotes than either the standard or chain cable restraints, thereby serving as a more humane method for capturing coyotes.

The results of this study provide valuable information to aid wildlife managers in choosing the most selective, effective, and humane type of cable foot-restraint when they must capture coyotes and traps are not available or legal to use for this purpose.

photo of bear crossing streetHuman-Black Bear Conflicts in Colorado— Human-wildlife conflict in urban environments is increasing through the United States, impacting species conservation, jeopardizing human livelihood and safety, and requiring increased resources from wildlife managers. An ongoing NWRC research project is studying black bear ( Ursus americanus) ecology and management in urban areas of Colorado to discover patterns of bear conflict, how conflict is influenced by the availability of both human food sources and natural food sources, and management strategies to reduce conflict. The goal of the study is to provide citizens and managers with a better understanding of why bears enter towns and offer tools for reducing conflict with the animals.

Because availability of garbage has been identified as key driver in human-bear conflict, a novel aspect of this research is focusing efforts on reducing garbage availability by altering human behavior. Research devoted to solving human-wildlife conflicts often focuses on managing wildlife, but there is a growing recognition that this approach typically provides only a temporary solution. Particularly in urban environments, changing human behavior would likely provide long-term solutions to growing problems with bears. Thus, part of this study is evaluating the effectiveness of education and law enforcement for altering human behavior.

Since the study's inception in 2005, production of natural foods available for bears has fluctuated dramatically each year. A key discovery of this research is that bears that may have used town environments in poor production years will keep away from town during good food years, dispelling the commonly held notion that “once a garbage bear, always a garbage bear.” Other results indicate that education and law enforcement as implemented in the study do very little to change human behavior. This important finding has led toward more focus on understanding the impact of urban areas on the local bear population (potentially positive or negative) and determining the impact of removal (translocation or lethal control).

Most importantly, this study illustrates the importance of understanding the ecological context of human-wildlife conflict, which can be critical for understanding the effectiveness of any management tool. Furthermore, the study shows that, without an experimental approach, conclusions about management success could be confounded. NWRC encourages the use of similar experiments when assessing the effectiveness of any management tool, be it focused on changing human behavior or bear behavior.

Select Foraging of Black Bears in Yosemite National Park—Black bears are one of the most adaptable large carnivores and readily raid human sources of food, such as trash cans, bird feeders, and campgrounds. However, it is unknown if bears forage selectively for these resources or just take advantage of random opportunities. NWRC scientists and collaborators at Yosemite National Park conducted a study on black bears over several years to determine whether they forage selectively for human food sources, particularly those found in cars.

From 2001 to 2007, bears broke into 908 vehicles at Yosemite National Park. Use of minivans was more than four times higher than expected (29% versus the 7% expected) based on the availability of different vehicle models. Researchers hypothesize that black bears selected minivans over other car models to maximize caloric gain and minimize costs by targeting vehicles with higher probabilities of payoff. In addition, minivans may be more likely to emit food odors—regardless of whether they contain food—because these vehicles are designed to hold large groups of people and children, which may increase the likelihood of them containing spilled food and drinks. Another potential reason bears selected minivans is that minivan owners may be more prone to leave large caches of food in their vehicles because they have the space to do so. Minivans also may be easier to break into than other vehicles. Lastly, scientists note the data could reflect the foraging decisions of a few individual animals that have developed a learned behavior for breaking into minivans.

The information gathered from this study will help managers develop strategies that include greater education efforts focused on vehicles carrying large groups of people and children, increased enforcement efforts for vehicles violating food storage regulations, and management of select problem bears in Yosemite National Park.

Snowshoe Hare Distribution and Abundance: Management Implications for Canada Lynx—Snowshoe hares ( Lepus americanus) are an showshoe hare in trapimportant prey species for Canada lynx ( Lynx canadensis) and are considered critical for the persistence of lynx populations. To support effective lynx conservation efforts, land management agencies need to determine snowshoe hare distribution and abundance. One accepted approach for estimating snowshoe hare abundance is the use of fecal pellet plot counts. In a recent study, NWRC and Utah State University researchers examined correlations between snowshoe hare density, as determined by mark-recapture estimates, and pellet plot counts on both uncleared plots and annually cleared plots in the Bridger-Teton National Forest in western Wyoming.

The results of the study show significant correlations between snowshoe hare density estimates and fecal pellet counts for both uncleared and annually cleared pellet counts; however, the relationship was stronger when using pellet counts from annually cleared plots. In addition, researchers found that omitting hard habitat edges (not used by hares) around trapping grids improved correlations between snowshoe hare density and fecal pellet counts for both uncleared plots and annually cleared plots. Though precision is sacrificed when using uncleared plots, researchers note that such plots are useful as a coarse index of habitat use by snowshoe hares. These results may be useful for identifying important foraging habitat for Canada lynx in western Wyoming, as well as for monitoring changes in hare populations among habitats and during prescribed management actions.

Endangered Species Protection

APHIS Wildlife Services conducts research and management activities to protect threatened and endangered wildlife species. These activities focus on protecting listed species from predation and competition with other wildlife, enhancing recovery programs, and increasing the public's ability to live with introduced and expanding populations of listed species.

photo of leatherback turtlePredators can have a severe impact on rare and endangered species through predation and competition. One of the primary threats to endangered sea turtle reproduction in Florida is nest predation by raccoons ( Procyon lotor) and armadillos (Dasypus novemcinctus). In a recent study, an NWRC scientist worked with representatives from APHIS Wildlife Services' Florida State Office; Ecological Associates, Inc.; and the Hobe Sound National Wildlife Refuge to examine the impacts of effective predator management during an exceptional nesting year at a sea turtle nesting beach in Florida.

Historically, without predator management up to 95% of turtle nests had been lost to predation each year, primarily by raccoons and, more recently, by armadillos. Although the refuge managers previously identified predator control as potentially the most important tool for increasing sea turtle reproduction, other staff duties at the refuge usually took higher precedence, and predator management was typically an ancillary duty. As a result, predation levels were held to only around 50%. However, recent predator control efforts, optimized by predator monitoring, have reduced predation to much lower levels (less than 20%). For example, in 2008, loggerhead turtle ( Caretta caretta) nesting was above average, and both green ( Chelonia mydas) and leatherback ( Dermochelys coriacea) turtles had record numbers of nests at twice or more the median number of nests usually deposited. Overall predation was held to 14.7% of nests.

As a result of this low predation level, an estimated 128,000 additional hatchlings emerged as compared to estimates associated with no predator management and historical predation rates (i.e., “no control” scenario). These efforts also resulted in an estimated 56,000 additional hatchlings over what researchers would have expected had predator management activities been conducted as ancillary duties rather than by experts who could focus solely on predator management (i.e., “control as ancillary duty” scenario). In addition, the study showed that the costs of effective predator management could be relatively low. The total investment for predator management by experts in this study was $12,000, which equates to a cost of only $0.09 per additional hatchling produced for the “no control” scenario and only $0.21 for the “control as ancillary duty” scenario.

In a similar study, NWRC and the Florida Department of Environmental Protection examined the biological and bioeconomic results of predator management relative to sea turtles and shorebirds on two adjacent barrier islands (Cayo Costa and North Captiva) along Florida's west coast. Both islands suffered severe nesting losses due to predation and disturbance by raccoons, while Cayo Costa also was impacted by a large population of feral swine. Prior to predator management, no least tern production occurred on either island, and sea turtle nest predation was 74 and 60%, respectively, for Cayo Costa and North Captiva. In 2007, predator management occurred on Cayo Costa, while North Captiva served as an untreated reference island. Cayo Costa produced 31 least terns, and sea turtle nest predation decreased to 15%. In contrast, North Captiva again had no least tern production, and sea turtle nest predation was 84%. In 2008, both islands received predator management. Cayo Costa and North Captiva produced 20 and 55 least terns and had 16% and 0% sea turtle nest predation, respectively. The entire cost for predator management by experts over the course of the study was $39,636, and the returns in additional production of least tern young and hatchling sea turtles were valued at over $1.1 million—resulting in a benefit-cost ratio of 27.8 for dollar expended.

Rodent-Proof Nest Box for Endangered Birds in Hawaii—The puaiohi, or small Kauai thrush ( Myadestes palmeri), is an endangered bird endemic to the island of Kauai, HI. The sole population of about 500 birds is currently restricted to remote, higher elevation areas of the Alakai Plateau. Puaiohi nest primarily on steep stream-side cliffs, and their distribution and abundance are limited partly by the availability of suitable nest sites. Black rats ( Rattus rattus) cause nest failure and mortality of nesting females, and ground-based rodent control has not been effective at reducing nest predation.

In 2007, researchers at the NWRC Hilo, HI, field station investigated whether artificial nest structures might be a viable alternative to rodent control by testing nest box designs to find one that is resistant to rats. In laboratory trials, the researchers evaluated three designs that were currently being deployed as artificial nest boxes for puaiohi and found that these structures are not rat resistant. From these initial results, researchers developed and tested an improved nest box design. Captive rats were unable to enter the new nest box, which was made from a 35-centimeter length of 15-centimeter-diameter plastic pipe with an overhanging entrance cut at a 49-degree angle (distance between the top and bottom lips of the pipe was too large for rats to reach while standing on top of the pipe). The overhang and size of the pipe prevented rats from climbing into the entrance. Field tests of the new nest box design are currently underway to determine whether wild birds can use the boxes successfully as protection against rats.

Monitoring Ethiopian Wolf Populations—The endangered Ethiopian wolf is considered to be the rarest canid in Africa. The species faces many threats and is particularly vulnerable to diseases such as rabies. A simple, low-technology means of monitoring Ethiopian wolf populations would greatly facilitate conservation efforts, as it could detect early population changes and behavior and signal a need for intervention.

To help address this issue, NWRC scientists partnered with Colorado State University and the Ethiopian Wolf Conservation Programme to test a passive tracking index methodology for use with Ethiopian wolves. The method uses counts of track intrusions into plots placed in the animals' routes of travel as the basis for calculating an index. While this approach has been successful when used for other species, researchers found that this approach did not work well for Ethiopian wolves, as the method did not intersect the wolves' activity patterns adequately. The low vegetation associated with Afro-alpine habitats offered little benefit for the wolves to travel roads. However, in a second trial of this approach among colonies of mole rats—a focus of wolf foraging activity—placing plots on mole-rat mounds was an efficient way to collect Ethiopian wolf plot intrusions for index calculations.

This plot placement method, coupled with passive tracking index calculations, might offer resource managers a cost-efficient tool that requires minimal equipment to monitor Ethiopian wolf populations on the Sanetti Plateau and other Afro-alpine habitats. Plot placement on roads in other Ethiopian wolf habitats where cross-country travel is more difficult might still be a viable means to collect track data as well, but requires further testing.

Estimating Coyote Numbers in Wyoming—Determining carnivore population sizes is a daunting task for wildlife biologists and managers. Currently, there is no known accepted technique for conducting censuses of coyote populations over large areas; however, APHIS Wildlife Services and its state partners are often asked to justify management activities based on their impacts on a species' population.

NWRC and collaborators with Utah State University and APHIS Wildlife Services examined the use of two methods for estimating coyote density and population size in Wyoming. During 2008, researchers documented density, or used home-range size and pack size to determine density, from coyote studies conducted in Wyoming, surrounding States, and areas with similar habitat. They also estimated deposition of scats along transects across the 97,818 square-mile (223,840 square-kilometer) state for comparison.

Analysis indicated that density estimates from past literature had a poor correlation with the density estimates from the scat transects, probably because of differences in methods of estimating density, differences in sampling regimes and observers used to collect data, and the more than 30-year timespan between the periods being compared.

Using estimates from the scat transects, the researchers estimated a statewide population of 49,854 ± 22,718 (±95 percent confidence interval) coyotes. The wide confidence interval was a result of the large variance in scat deposition among transects. When researchers assumed a high survival rate (i.e., no or low natural and anthropogenic mortality), they calculated an estimate of 86,601 ± 22,718 coyotes for the state. While scientists initially attempted to sample at least 20 transects within each strata, they found that a minimum of 40 transects per strata was needed to reduce the variance and resulting confidence intervals.

This was the first attempt to estimate the size of a coyote population over a very large area. Future research will continue to examine methods of estimating coyote population size which will assist state managers and WS to document efficacy of removal activities on coyote populations.

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