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IntroductionThe Agouti paca is the second-largest rodent species behind the Capybara, weighing up to 12kg and reaching a head to tail length of 79.5cm. Pacas currently range from East-Central Mexico to Paraguay where it is commonly referred to as tepezcuintle. They have course brown to black fur on the upper body and white on the underbelly. A pattern of three to five rows of white spots along its sides distinguishes it from the closely related Agouti (Guatusa), which is a slightly smaller rodent species that is solid brown in color. The paca has a robust body with strong legs that have four digits in the forefeet and five in the hind feet. The zygomatic arch of the paca is expanded and acts as a specialized resonating chamber, a characteristic that is lacking in all other mammals. They prefer to live in heavily forested areas near water which they are comfortable swimming in and will use as an escape route to avoid predators. As a nocturnal species they spend their day in a shallow burrow, which can be located on steep slopes, on banks, under rocks or among tree roots. They emerge from their burrows at dusk to forage for a combination of foods that includes: fallen fruit, seeds, roots, stems and leaves. Because of thier diet paca play an important role in forest dynamics as seed predators and dispersers.They are also considered agricultural pests and killed for this reason. In addition, pacas are commonly hunted for their meat which is considered a delicacy and can be sold for prices much higher than other meats. Since their meat is so highly prized, domestication has been investigated. Between 1983 and 1990 the Smithsonian Tropical Research Institute in Panama carried out an experimental program to domesticate pacas. Although they are naturally aggressive and asocial, the Institute found that the socialization process can be altered if done during a critical period of infancy. Within one generation it is possible to have a non-aggressive social group of one male, several females and their offspring. The elusive, nocturnal nature of paca makes them difficult to study in the field. Common methods usually include trapping and radiotelemetry. Radiotelemetry is an efficient way to study the movements and home ranges of paca, but it is also an incredibly time consuming and expensive method. A new technique to track the movements of nocturnal rodents was introduced by Lemen and Freeman in 1985. This technique involved dusting the trapped rodents with fluorescent pigments and then checking the trail of pigment from the rodents’ movements with an ultraviolet light. Their study revealed that the rodent did not restrict its activity to the ground as previously thought, but actually climbs on vegetation to forage. Using fluorescent pigments is a relatively simple and inexpensive method that is harmless to the animal and environment. It is non-toxic and quickly washes away and degrades with rainfall. This technique and variations of it has been used in many different studies. For instance, terrestrial movements of the Spadefoot Toad were studied by applying pigments diluted with paraffin oil to the toads’ legs and checking the tracks left with an ultraviolet light. Longland and Clements (1995) used fluorescent pigments in two different ways to study seed caching by rodents. The first involved dusting seeds with the pigment and locating the pigmented spot on the ground where it was stored. The second involved not only dusting the seeds at a bait station but also placing pigment where the rodent would stand to get the seeds. The pigmented footprints allowed the researchers to record details of seed transport, caching and the location of rodent burrows. Placing the powder in the path of the rodent is a noninvasive method that does not require trapping and does not alter the behavior of the animal being studied. It is this method that was implemented in the following study which investigated the trail use and movement patterns of Agouti paca.
MethodsThe study was conducted in the small agricultural community of Mastatal in the Pacific lowlands of Central Costa Rica. Two trail systems were used: Leo’s trail system which are generally higher in elevation than the other trails, have many fruit trees and consist of primary and secondary forests and Jeannie’s trails that are lower in elevation and consists of secondary forests. Elevation measurements were estimated from the trail system maps provided by Rancho Mastatal Environmental Learning Center. Local trackers were used to become familiar with the trail systems, locate possible Tepezcuintle (paca) trails and identify Tepezcuintle, Guatusa (Agouti) and Pizote (White-nosed Coati) footprints, all of which could have used the trails. Four possible paca trails were identified and flagged within Leo’s trail system and five in Jeannie’s. The flagged trails were all located along the main (human) trails. Red fluorescent pigment from Risk Reactor, Ltd. was used dry with no modifications and was placed to cover the ground uniformly in an area of 3.24 to 9.0 square centimeters depending on the width of the trail which was 1.8 to 3.0 centimeters. The pigment was applied just before dusk and checked the next morning between 3:00 and 5:30 AM using an ultraviolet light to locate the trail of pigment on the ground. Measurements were taken for each turn made and the total distance the pigment was visible for. The type of powder disturbance was noted along with the type of tracks and if the main trail was utilized.
ResultsThe study trails at Leo’s varied in elevation from 225 to 1200M. Two of the four trails marked showed powder disturbance. Trail number 1 was at approximately 500M, the pigment was dispersed 0.7M up on the bushes and 1.0 straight along the trail in the direction of the stream for a total distance of 1.7M. The main trail was not utilized and according to the local tracker the tracks were from Guatusa or Pizote. Trail number 2 and 3 at 1000 and 1200M elevation showed no powder disturbance. Trail number 4 was at approximately 225M elevation, the pigment was dispersed along the trail and toenail impressions were evident in the applied powder. The trail of pigment progressed 3.1M straight then 1.0M right, curved 3.0M to the left and then curved 2.0 right towards a feeding ground of mangoes, for a total distance of 9.1M. The main trail was used to access this trail and the tracker determined it to be paca (Table 1).
The study trails at Jeannie’s varied in elevation from 150 to 300M. Three out of five of the trails showed powder disturbance. Trail number 1 was approximately 190M in elevation; the pigment was dispersed along the trail and on top of a log with some clearly defined footprints. The trail of pigment progressed in the direction of the stream; it curved 5.0M left, 1.0M on the log to the left, 1.2M right and 3.0M right, for a total of 10.2M. The main trail was utilized and the footprints were determined to be paca. Trail 2 and 4 at approximately 300 and 150M in elevation had no powder disturbance. Trail 3 at approximately 180M had powder streaks across the main trail for 3.0M and then curved left 3.5M on the animal trail, 2.5M to the right and 6.0M right, for a total distance of 15M. The streaks were likely from a tail or underbelly drag and therefore could not be made by paca. At approximately 150M in elevation, trail 5 had powder disturbance that went straight for 1.0M. The main trail was used but the type of tracks could not be determined (Table 2). Table 2: Jeannie's Trail System
DiscussionOf the nine study trails, five had powder disturbance with two of those identified as paca, two unknown and one as Pizote or Guatusa. The two trails identified as paca: number 4 at Leo’s and number 1 at Jeannie’s are lower in elevation and in close proximity to a water source (Table 1 and 2). Trail 4 and 5 at Jeannie’s were approximately 150M in elevation, however, the water source was further away from these trails, which were not utilized (Table 2). The same is true for trail 2 and 3 at Leo’s where the trails are at higher elevations and further from water source (Table 1). Proximity to a water source appears to be a predominant factor in determining the trail use of paca. Four of the five trails disturbed did utilize the main (human) trail. Although only two of these were determined to be used by paca, it does show that these animals and others do not exclusively use their own trails but those made by humans or other animals. It could not be determined from this study to what extent the main trail was used. Only one of the five trails with disturbance indicated movements above the ground and these footprints were made by either Guatusa or Pizote (Table 1, trail 1). This study found that the paca moves along the trail only going over small branches and logs rather than climbing up onto bushes. This would indicate that the paca was utilizing these trails to reach a feeding ground or water rather than foraging along the trail. The longest pigmented trail was 15M on a trail with unknown animal tracks (Table 2, trail 3). Of the two paca trails, the longest pigmented trail was 10.2M. These trails of pigment were very short compared to reported values in previous studies. The short distances of pigment disturbance seen in this study are likely from many causes. For instance, the terrain and ground litter probably inhibited the pigment from being tracked as far as if it were a smooth, level surface. In addition, the humidity may have affected how well the pigment was picked up by the animals’ feet. Future studies could use the powder in different ways to determine which method results in the maximum amount of pigment picked up and displaced. In this study the pigment was used dry but perhaps if it was mixed with a different substance the results would yield longer pigmented trails. Another important factor in this study was the rainfall. During the study period it rained nearly everyday which limited the application of pigment and therefore the number of trails studied. The dry season may be a better time to employ this method. Future studies would require a longer period of time and a larger number of trails studied. As stated earlier, domestication of paca has been successful; this was evident in several households in Mastatal where they were raising paca as a source of meat for their families. The two households I visited plus two others were funded in 2002 by Fundación Ecotrópica, a non-profit institution, and guided by the Ministry of the Environment and Energy (MINAE) who together provided these households with enclosures to house the paca, one male and several females and husbandry guidelines to follow. After the initial set-up, housing and caring for the pacas’ is a relatively inexpensive endeavor. The owners provide them with fresh leaves, fruits and seeds that can be harvested from their land or the surrounding forest and they are given leftovers of rice and beans which they are said to love. Domestication could help reduce the hunting pressure of wild pacas and provide much needed protein for small farmers. A group of pacas can provide more meat at shorter intervals than raising a cow to slaughter and does not contribute to deforestation. According to the MINAE poaching of the paca has declined since 2002 when the local domestication program began and La Cangreja, a protected park near Mastatal attained National Park status.
I would like to thank Dr. John Banks for the opportunity to conduct research in Costa Rica and his help during an early morning data collection hike. Thanks to Lia Wetzstein for her consultation on rodent studies and the potential uses of fluorescent pigments. Thank you to Tom McDonald for his guidance and local expertise. I thank Tim and Robin for their hospitality and for their help as interpreters several times. A special thanks to Don Mario and Chapo for their guidance in the field and their expert local knowledge. Thanks also to Catherine Crook for her help in data collection during an early morning hike.
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