Behavior of black-tailed prairie dogs toward different predators
James R. Thiele, Department of Biology, University of Nebraska at Kearney, Kearney, NE 68849. Sam A. Vanourney, Department of Biology, University of Nebraska at Kearney, Kearney, NE 68849. Mentor: Joseph T. Springer, Professor, Department of Biology, University of Nebraska at Kearney, Kearney, NE 68849. Email: springerj@unk.edu)
To Cite This Paper:.
Thiele, J. R., and S. A. Vanourney. 2000. Behavior of black-tailed prairie dogs toward different predators. Senior Research Thesis, Department of Biology, University of Nebraska at Kearney, Kearney, Nebraska.
ABSTRACTArtificially staged encounters between prairie dogs and their snake and badger predators were conducted at two sites in southern Nebraska. Three artificially staged badger/prairie dog encounters at Prairie Dog Federal Waterfowl Protection Area (PDFWPA) were compared to two at Stormer Ford Dog Town. The prairie dogs at Stormer Ford Dog Town behaved more frightened by the badger because they fled down their burrows sooner than at PDFWPA. Three snake/prairie dog experiments were conducted at each site. The behaviors observed during these interactions were compared to those reported by Halpin (1983) and Loughry (1987).
Black-tailed prairie dogs (Cynomys ludovicianus) use visual and vocal cues to communicate danger to each other. The characteristic avoidance response displayed by these small mammals to the approach and presence of nonhuman predators and humans, consists of an alarm bark that serves to warn other group members of impending danger, followed by running to the burrow and hiding (Adams, Lengas, and Bekoff, 1987). The complexity and variability of avoidance and antipredator responses displayed by black-tailed prairie dogs to snakes has been studied by Halpin (1983) and Loughry (1987a, 1987b, 1988, 1989). Hoogland (1981) used a stuffed mink (Mustela vison ) and stuffed badgers (Taxidea taxus ) to study the response of prairie dogs to predators.
Black-tailed prairie dogs (Cynomys ludovicianus) use visual and vocal cues to communicate danger to each other. The characteristic avoidance response displayed by these small mammals to the approach and presence of nonhuman predators and humans, consists of an alarm bark that serves to warn other group members of impending danger, followed by running to the burrow and hiding (Adams, Lengas, and Bekoff, 1987). The complexity and variability of avoidance and antipredator responses displayed by black-tailed prairie dogs to snakes has been studied by Halpin (1983) and Loughry (1987a, 1987b, 1988, 1989). Hoogland (1981) used a stuffed mink (Mustela vison ) and stuffed badgers (Taxidea taxus ) to study the response of prairie dogs to predators. Prairie dogs are large (700-1500g), diurnal, colonial rodents. The typical prairie dog colony is subdivided into two or more wards. Residents of one ward can sometimes see or hear residents of an adjacent ward, but communication and interactions between wards are rare (King, 1955; Hoogland, 1981). Black-tailed prairie dogs within a ward are organized into social units known as coteries. The typical coterie contains a single adult male and his harem of 1-6 females, along with yearlings and juveniles. Coterie members restrict foraging and other activities to well defined coterie territory that contains scores of burrow entrances. The main size of a coterie territory is about 0.26 ha (King 1955). The purpose of our study is to observe predatory response of the black-tailed prairie dog. The bull snake is a potential predator, (Loughry, 1987a, 1987c, 1988; Halpin 1983) whereas the badger is a known predator (Cambell and Clark, 1981; Hoogland, 1981). For the experiment with the stuffed snake and badger, we assumed that the prairie dogs would respond to the stuffed specimens as they would to live predators. Experiments were conducted mid-April of 2000 before pre-pup emergence.
STUDY AREAObservations were made at two separate prairie dog colonies in southern Nebraska. The first colony comprising of 1.25 ha is located 5 miles south of Axtell at Prairie Dog Federal Waterfowl Production Area (PDFWPA). The PDFWPA (Fig. 4), located less than 50 yards from a frequently traveled dirt road, is wide open pasture heavily grazed by cattle with no trees or shrubs present which provides unlimited visibility. The second colony comprising of 4 ha is Stormer Ford Dog Town (Fig. 5) located near Harlan County Reservoir north of the dam. The Stormer Ford Dog Town is ungrazed and surrounded by intense cover (tall grass, thickets, and trees). Several burrows are located within 3 meters of this cover and a frequently traveled paved road runs partially through the main colony. Since both colonies are small, pulls were conducted where highest probability of interaction would occur. 
MATERIALS AND METHODSObservations were made at the sites from 14 April to 20 April, 2000. All data were obtained using a JVC Compact VHS Camcorder, which ran continuously during each pull. Observations at the PDFWPA site were made from the cab of a pickup and observations at the Stormer Ford Dog Town were made from the prairie dog viewing area.
Snake ExperimentAll previous studies involving prairie dog encounters with snakes were observed involving natural encounters or the use of a tethered snake (Hennessey, 1981). To study the responses of prairie dogs to snakes, we used a stuffed bull snake (Pituophis melaneucus sayi). The bull snake consisted of a skin taped to a toy rubber snake wrapped in fabric to add girth. Several days before the experiment, a burlap piece was placed 5 meters from an outermost entrance in order for the prairie dogs to become habituated with it. At each trial, the bull snake was placed under the burlap and pulled from it by means of twine by one of us in concealment while the other videotaped. Videotaping and pulls began when there was no sign of above ground disturbance. The snake was pulled at a rate of one-half meter every two seconds and continued until the first alert signal of an alert posture or a sudden run was observed. Pulling began and stopped randomly to simulate live snake movement. It was usually stopped when prairie dogs approached to simulate a snake stopping to coil when danger is near. This pattern was repeated until the snake had traveled through the entire town and was 5 meters outside of the colony. During the experiment the snakes were randomly given a quick jerk from the resting position to simulate a strike directed toward nearby prairie dogs, this will be referred to as a "strike" in this paper.
Badger ExperimentTo simulate the live badger we used a mounted specimen that was in a standing posture. The badger was mounted on a cardboard sled allowing for easy maneuverability. Before each pull the badger was concealed under a burlap sack that had been place there several days earlier as described above. The badger was pulled from concealment with twine that led from the predator to one of us at the pulling position. The puller recorded information with pen and paper while the other recorded activities through the video camera. Pulls were made when there were no signs of disturbances among the above ground foraging residents. The badger was positioned at a peripheral ward position approximately 50 yards from an outermost burrow entrance. The badger was pulled at a constant rate until the first vocal alarm was sounded. It then was allowed to sit for about 20 seconds and then pulled again about 5 meters before resting another 20 seconds. This procedure was followed as the badger continued through the town. The experiment stopped when the last encountered prairie dog fled to its burrow. The badger was positioned in a spot where we thought the most encounters would occur while being pulled through the town. Three measurements were taken in regard to prairie dog and badger encounters. One measurement was the distance pulled before any resident became alarmed of the incoming predator while another measured the predator to prey distance before prairie dogs fled to a mound. A last measurement was the distance at which the prairie dog went down the burrow due to the incoming predator.
RESULTSWhen a prairie dog detects a predator, it immediately runs to a burrow mound or assumes an alert posture that provides a visual alarm to other ward residents. A visual alarm usually offers the first sign of danger during a predatory attack. Individuals seem to watch close neighbors for visual alarms and respond quickly when one is given. After detecting a predator and giving a visual alarm, a prairie dog sometimes then gives a series of alarm calls (Waring 1970). Prairie dogs do not give alarm calls in response to any animal that approaches a ward, but only in response to their known predators such as coyotes, badgers, black-footed ferrets, golden eagles, and prairie falcons (Hoogland, 1981).
Snake ExperimentPull 1. PDFWPA. 17 April 2000. Shortly after the pull began, two quick alarm barks were given. One prairie dog sat and watched in an alert position while others continued foraging. The alerted prairie dog approached the snake from the rear and followed it for a meter at a distance of four body lengths, then turned to jump-yip (see Smith et al., 1976 for description). Both high and low amplitude jump-yips (Owings and Owings, 1979) were observed throughout the pull. As the snake advanced forward, another prairie dog approached the now resting snake's head with an elongated, tense body posture until within two body lengths of the snake. As Halpin (1983) described, these approaches were accompanied by head-bobbing movements during which the prairie dog repeatedly stretched and shortened its neck, while at the same time making rocking movements with its body towards and away from the snake. After almost 35 seconds, the prairie dog retreated and jump-yipped. The same prairie dog pursued the snake each time it started forward behaving in the same manner described above. Each approach is with an elongate, tense body followed by a short retreat ending in one to three jump-yips. The prairie dog lost interest in the snake if it rested over a minute so movement would begin when the prairie dog walked away. A couple of times when the prairie dog was within a body length of the snake a quick jerk would be given to simulate a strike. During this encounter the prairie dog would quickly jump back only to return directly to the snake. Pull 2. Stormer Ford Dog Town. 17 April 2000. Immediately after the snake left the concealment of the burlap, an alarm was sounded and many prairie dogs retreated to their mounds. The snake continued 15 feet forward while two of the closest prairie dogs continually barked. One prairie dog charged 20 feet, stopped, charged another 10 feet, stopped, and charged another 6 feet. It approached cautiously in the elongated posture described previously before retreating. While wagging its tail strait up, the prairie dog approached with its head outstretched, retreated, and jump-yipped twice. The prairie dog repeatedly approached, continually barked and retreated 3-4 meters each time the snake moved. The interaction lasted twelve minutes and ended when the snake had traveled through the prairie dog's area. Pull 3. PDFWPA. 18 May 2000. The snake was detected shortly after leaving the concealment of the burlap. Several prairie dogs in the area retreated to their mounds, looked for danger, and continued feeding moments later. One prairie dog moved toward the front of the snakes in an elongated posture described in pull 1. A prairie dog watching from approximately 5 meters away, jump-yipped twice then resumed feeding. The snake struck and the closest prairie dog jumped back and ran to a mound. It immediately approached the snake, always toward the snake's head, in an elongated posture. Again, the snake struck and the prairie dog jumped back but stayed near the snake. The snake began forward and another prairie dog joined the first one near the snake. They both approached the snake as described previously with one continually head-bobbing while the other jump-yipped twice. The two interacted with the snake for another seven minutes in the behavior described previously while another prairie dog approached the snake's rear. This prairie dog was within three body lengths, retreated and jump-yipped. The other two prairie dogs followed the snake another couple meters, jump-yipped and returned to foraging. Pull 4. Stormer Ford Dog Town. 18 April 2000. The snake was detected after moving forward one meter. An alarm call was sounded and the three closest prairie dogs ran to their burrows. After one minute forty seconds a prairie dog walked off its mound toward the snake with tail up. It jumps as the snake struck, retreated, jump-yipped and returns to the snake. The prairie dog then approached with elongated body, took a step forward, then back while head-bobbing, jump-yipped then walked off. As the snake began to move, the prairie dog approached and retreated several times and stopped to bark from a nearby mound. While on all four feet, the prairie dog thumped its back foot a couple of seconds while tail wagging. It repeated this twice before running back to the mound it originally came from and stood in an alert position continually barking until the snake had left the area. Pull 5. PDFWPA. 19 May 2000. The snake went unnoticed for about 15 meters before an alarm call was sounded. Three prairie dogs ran to their mounds and watched the snake pass before leaving the mounds. As the snake moved forward, a prairie dog ran toward it until approximately six body lengths away, approached to four body lengths and performed seven jump-yips. The prairie dog walked away jump-yipping after the snake did not move. As the snake continued along, the same prairie dog approached the snake as described in encounter 1 and moved very close while continually head-bobbing. Each time the snake moved, this series of events occurred. Once after the snake remained still, the prairie dog moved away jump-yipping twice and resumed feeding after following the snake for ten minutes. As the snake continued forward, a new prairie dog, previously on its mound, approached the snake to four body lengths, fled back to mound and jump-yips only to repeat this behavior once more. Closer toward the edge of town another prairie dog followed close behind the snake for a couple of meters, then returned to feeding. Pull 6. Stormer Ford Dog Town. 17 April 2000. A prairie dog sighted the snake immediately and began barking. The only other prairie dog in the area retreated and never returned. The remaining prairie dog approached the snake as described by Haplin (1983). It repeatedly head-bobbed until within a few inches of the snake. It then turned, jump-yipped and ran away jump-yipping. As the snake moved forward, the prairie dog watched from an alert position and barked but did not return to the snake. It continually barked about a minute and returned to foraging.
Badger ExperimentAfter observing badger/prairie dog interactions at PDFWPA three separate measurements were made. Obtaining this data involved three trial runs. Measurements were found using human walking paces (10 paces=7.5 meters). Each time the badger was concealed under a burlap sack 55-60 paces from the nearest outside burrow. The mean distance of the badger from the first prairie dog to give an alarm call was 33 meters (see Fig. 1). 
The next measurement that was taken was the distance between the badger and the mound that each prairie dog fled to as the predator moved into the colony. The mean distance from the badger to the mound where a prairie dog fled was 22.2 meters (see Fig. 2). A more logical measurement would be the distance from badger to prairie dog when the prairie dog fled to a burrow.
However, it was difficult to assign the exact position of each foraging prairie dog after the trial run. It was simpler to measure distances to a mound. Since most prairie dogs forage within a few paces of their burrow, there should not be much discrepancy. We scared many prairie dogs into their burrows when we first appeared at the site. This kept the prairie dogs close to their burrows because we conducted our experiment shortly after they reappeared. The last measurement was distance from prairie dog to badger when the prairie dog disappeared into a burrow. The mean distance for this measurement was 4.5 meters (see Fig. 3). 
At the Stormer Ford Dog Town, only two trials were observed. We tried one other trial run, but when we set up our experimental run the prairie dogs were frightened by us. These prairie dogs would have been in direct interaction with the badger and in turn did not reappear for over an hour. We could not anticipate how much longer the prairie dogs would stay underground, so we did not attempt this run. The colony was bordered with thick cover at this site and some mounds were only a few paces away from tall grass, thickets, and cedar trees. The badger was hidden in this thick vegetation where it could not be seen. The badger also would come into appearance much closer than at PDFWPA. The mean distance from the badger to the first prairie dog which emitted an alarm call was 17.6 meters (Fig. 1). The mean distance from the badger to the mound in which prairie dogs fled was 16 meters (Fig. 2). The initial closeness at which the badger appears stimulates a faster flee to a mound and not as long of a time in alert posture from a foraging position. The distance in which the badger caused the prairie dog to disappear down a burrow was 6.26 meters (Fig. 3). This distance was larger than PDFWPA. In addition, the time in which the first prairie dog noticed the badger at Stormer Ford was a few seconds after it appeared from concealment. At PDFWPA, it took approximately 15-30 seconds until the badger was noticed by the first prairie dog. This correlates with distance from which the badger was originally concealed. Due to differences in the surroundings of each town, legitimate comparisons are difficult involving prairie dog/badger interactions. In our opinion, the PDFWPA seems to be more natural in terms of the habitat that prairie dogs are accustomed to.
DISCUSSIONUpon hearing an antipredator call, prairie dogs stop activity and scan the area for predators. When no danger seems to be present, they resume their activities. If the listening prairie dogs, detects a predator, it runs to a burrow mound and sometimes initiates its own antipredator call. Only rarely does a prairie dog start calling in response to another antipredator call without first detecting the predator itself (Hoogland 1995). Contrary to popular belief, prairie dogs do not automatically submerge into a burrow after hearing or giving an antipredator call. Alerted individuals usually remain on burrow mounds and carefully watch the predator until it departs. Only when the predator comes close, sometimes as close as 5 meters, does a prairie dog usually submerge. If a prairie dog stays aboveground and sees the predator depart, then it can resume foraging immediately. Though once forced underground, the prairie dog cannot easily detect whether the predator is still in the colony. (Hoogland 1995)
Snake ExperimentThe similarities between the encounters reported here and those described by Haplin (1983) are striking. We did observe foot-thumping which he reported not seeing which was a major part of Owings and Owings 1979 study. We also observed as Loughry (1987) reports, snake-directed individuals are engaged in those activities typically labeled harassing, while snake-indirected individuals monitor an encounter without actively participating in it. Variation was observed, but one main pattern usually occurred. It was common for the prairie dogs to approach in the manner described by Haplin, followed by a retreat almost always ending in one to three jump-yips. One interesting observation was that prairie dogs were very curious about the snake and would move toward it. It was treated more with curiosity than fear and did not appear to be a threat to the prairie dogs.
Badger ExperimentBefore performing the experiment with the badger, we expected a different reaction from the prairie dogs. We expected the prairie dogs to be much more nervous and flee much sooner as well as more often. However, after our observations the results indicate that they let the predator get very close before disappearing down a burrow. As Hoogland (1995) found, prairie dogs let predators come within 5 meters. We saw similar results, which leads us to believe that this was normal behavior. We were unable to find any studies that observed distances between prairie dog and badger interactions. Some articles that we looked at observed the vocalizations but not what we experimented, which is unfortunate for matters involving comparison.
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Thiele, J. R., and S. A. Vanourney. 2000. Behavior of black-tailed prairie dogs toward different predators. Senior Research Thesis, Department of Biology, University of Nebraska at Kearney, Kearney, Nebraska. |