Field Anesthesia and Capture Techniques of Free-Ranging Mantled Howling Monkeys (Alouatta paliatta) in Costa Rica
American Association of Zoo Veterinarians Conference 1999

R. Scott Larsen1, DVM; Anneke Moresco1, MS, DVM; Kenneth E. Glander2, PhD

1College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, USA; 2Duke University Primate Center, Durham, NC, USA


In July of 1998, 83 anesthetic procedures were performed on 68 free-ranging mantled howling monkeys (Alouatta paliatta). Animals were safely anesthetized using 42±8 mg/kg of Telazol® administered with a Pneu-dart® system. Morbidity was associated with inappropriate dart placement and injection of infants and juveniles with adult dosages. All animals recovered with supportive care and there were no mortalities.


Long-term behavioral and demographic studies of free-living primates require the ability to recognize individual animals.2 Such recognition is particularly difficult in arboreal primates as there is always a substantial distance between observer and subjects and because foliage often makes visual contact difficult. Marking of individuals greatly enhances the ability of field researchers to accurately identify animals. However, this marking requires safe capture that minimizes morbidity, mortality and makes minimal changes in the animals’ behavior and environment.

Comprehensive health assessments of free-ranging primates have been infrequently reported.3 Such information enhances modern conservation efforts by providing baseline data for evaluation of environmental impacts on the health and wellbeing of primate species.3 In July of 1998, veterinarians and primatologists collaborated to combine health evaluations with behavioral and demographic studies of free-ranging mantled howling monkeys. The results of the health assessments are still being compiled and will be reported elsewhere. This report documents the field techniques used to safely anesthetize and capture free-ranging mantled howling monkeys in Costa Rica. Using these techniques, researchers were able to safely and accurately perform morphometric measurements, create dental impressions, collect blood and feces, perform gastric lavage, insert transponder chips, and apply tattoos, identifying collars, and bracelets.

Materials and Methods

Eighty-three anesthetic procedures were performed on 68 individual mantled howling monkeys. Of these 83 procedures, 66 were accomplished under “routine circumstances,” while 17 occurred with “special circumstances.” Criteria for “routine anesthesia” included: 1) adult animal; 2) one dart-delivered anesthetic injection for capture; and 3) injection in target area (hindleg, tail or tailhead).

Monkeys were anesthetized before 1100 hr and after 1400 hr to minimize temperature stress and maximize visibility. Anesthetic was delivered using a carbon dioxide powered, modified Pneu-Dart™ system (Pneu-Dart, Inc., Williamsport, PA, USA). Pneu-darts with 9-mm needles were used. For adult monkeys, each dart was filled with 0.8 ml (200 mg) of Telazol® (tiletamine HCl and zolazepam HCl, Fort Dodge Laboratories, Fort Dodge, IA, USA; 250 mg/ml) in order to administer a dose of 42±8 mg/kg (range = 29–69 mg/kg). Animal and shot selection were based on the animal's size, location, and presentation. Shots were only attempted at animals that were not moving and that were not facing the shooter. Clear visualization of the hindquarters was essential; females holding infants were not shot if the infant was on or around the targeted area on the mother. Shots were avoided if the animal could move into trees with branches over a body of water. Animals were darted from distances of 10–30 m.

Induction times were 6.0±4.4 min (range = 1–18 min). As animals fell from the trees, they were caught in nylon mesh nets (camper’s hammocks) that were held by two to three people. Occasionally animals were caught “by hand”; however, it is felt that this technique often provides unnecessary risk to monkeys and to personnel. A few animals were not caught by personnel and fell to the ground. Falling distances ranged from 5–20 m. Animals showed complete muscle relaxation during and after such falls; no obvious injuries were associated with impact.

Several darted animals became anesthetized but did not fall from the tree. In these cases, the tree had to be climbed or the branch on which the animal was resting had to be shaken with a saw attached to the end of an aluminum pole (Azel Corp., Costa Mesa, CA, USA). The aluminum poles were composed of 1.75 m sections that were bolted together until long enough to reach the darted animal. This pole system has been used to reach animals up to 30 m off of the ground; however, considerable amounts of practice and patience are necessary to manipulate this length of pole.

Times from dart injection to being on the ground were 9.0±6.2 min (range = 1–24 min). Once an animal was on the ground, physical parameters were measured. Heart rate, respiration, and body temperature were immediately measured and then monitored intermittently during the remainder of the anesthesia. Animals were transported by van to a central, shaded processing area. Forty-three monkeys that were insufficiently anesthetized for weighing, marking, or blood collection were given supplementary injections of Telazol® (3.5–8.5 mg/kg). Supplemental injections were necessary approximately 1 hr (x = 62 min; range = 28–145 min) after the first injection. Only two of these 66 animals required a third injection of Telazol® (3.5–8.5 mg/kg).

Atropine (0.014–0.022 mg/kg) was immediately administered to monkeys with heart rates less than 100 beats/min and to all monkeys receiving supplemental injections of Telazol®. Temperature was closely monitored in all animals. Any rectal temperature greater than 39.0°C was treated by applying water or rubbing alcohol under the arms and legs; any rectal temperature greater than 40.0°C was treated by immersing the caudal half of the animal in a bucket of cool water. The body temperature of most monkeys gradually decreased (from 38.1±1.0°C to 37.3±1.0°C) over the course of anesthesia. Variability in heart rate (140±25 bpm; range = 88–220 bpm) was noted, but increased (153±29 bpm) in response to atropine administration. Respiratory rate remained constant (27±7.5 breaths/min; range = 16–64 breaths/min) for most animals.

After all procedures had been completed, the animals were allowed to partially recover in a relatively cool, shaded spot where they were constantly observed. All animals maintained a swallow reflex throughout anesthesia and, once sternal, were allowed to sip small amounts of water given in a syringe. Once the monkeys began showing signs of deliberate limb movement, they were placed in burlap bags located in a relatively cool, shaded place. Here they were monitored until they had recovered enough to climb a tree a height of 2 m. The burlap bags confined the monkeys and reduced the amount of visual stimulation they received, but did not restrict their ability to breathe. Recovery times varied between 30 min and 4 hr and were dependent on Telazol® dosage. Once animals had recovered, they were transported to the sight of their capture and released. Animals that had not recovered by 1 hr before dusk, were kept confined in the bags overnight and released the following morning.

The 17 animals that were anesthetized under “special circumstances” included: 1) Five juveniles and infants that were hand-injected; 2) four animals that required more than one dart-delivered injection; 3) three adults that received intra-abdominal injections; and 4) four juveniles and infants that received dart-delivered injections of adult dosages.

Adequate anesthesia of juveniles and infants was accomplished with hand injection of 2.5–20 mg/kg of Telazol®. Of all the adults that were darted, three required a second dart-administered injection of Telazol® (200 mg), while one monkey required a total of three injections. Vital parameters of these animals did not differ from those anesthetized with one injection and their recovery times were not prolonged (30 min to 2 hr). All three animals that received intra-abdominal injections had somewhat prolonged recovery times (3–4 hr). One of these animals appeared pale when first examined, but its mucus membranes gradually became pink. No other problems were noted.

The greatest amount of morbidity was associated with the three juveniles and two infants that were accidentally darted with adult dosages of Telazol® (77, 80, 133, 274, and 600 mg/kg respectively). These animals experienced varying degrees of bradycardia and respiratory depression. Bradycardia was responsive to treatment with atropine (0.01–0.03 mg/kg); respiratory depression was responsive to treatment with Dopram® (doxapram HCl, A.H. Robins Co., Richmond, VA, USA; 2–4 mg/kg). The three juveniles recovered approximately 4 hr post-injection, while the two infants required supportive care overnight. It is unknown whether the smallest infant (0.33 kg) received the full contents of the dart; if this did occur, it received a dose of 600 mg/kg Telazol®. Over the course of 8 hr, this infant required four doses of atropine (0.04 mg/kg) and two doses of Dopram® (4 mg/kg). It was also given balanced electrolyte and dextrose solutions administered subcutaneously. It was kept warm and monitored overnight. The following morning it appeared fully conscious, was moving vigorously, made contact vocalizations, and was observed to suckle from its mother. Contact vocalization was a critical parameter in evaluating the readiness of an infant for release, as howler mothers will not respond to infants that do not emit these calls.


The dosages used to anesthetize these monkeys were much higher than those reported for captive animals. Doses of 2.6–4.4 mg/kg Telazol® have been reported to be effective on captive howling monkeys4; however, field experience has suggested that higher dosages are necessary in free-ranging animals.1,2 These differences are most likely due to the conditions of field anesthesia. During this study, anesthetized howling monkeys almost always became unconscious while still in a tree. The last part of the body to relax was the tail, and they often kept a firm tail grip on a branch while they were unconscious. This muscle tone provides a problem in field conditions and higher doses of anesthetic are often needed in order to allow for tail relaxation. Higher dosages were also used to decrease induction times. Variations in foliage thickness and understory terrain provide challenges to safely tracking monkeys that have been darted. During this study, visual contact was lost with only one animal after it had been darted. Other darted monkeys had quick induction times which prevented escapes and minimized the risk that monkeys would become anesthetized once visual contact with them had been lost. Other investigations have reported the successful use of lower dosages of Telazol® for the field anesthesia of arboreal primates.1,3,5 One such study in howler monkeys, using 15–30 mg/kg Telazol®, expressly excluded the results of animals that required more than one dart.1 Another investigation used lower dosages (10 mg/kg) on wild howlers that had already been captured.5 Yet another study used dosages of 12–19 mg/kg of Telazol® in spider monkeys, but only reported on eight animals; the investigators of this report also used a Telinject® darting system, which, with lighter darts, may provide problems when darting through heavy foliage.3

Telazol® is an appropriate anesthetic as it has a wide safety margin, provides effective anesthesia and analgesia, and provides adequate muscle relaxation in most animals.4 One of the authors (KEG) has previously used other anesthetics in arboreal primates with less desirable results. The use of ketamine HCl (alone or in combination with xylazine HCl, acepromazine HCl or diazepam) has not provided adequate relaxation, resulting in monkeys that are more difficult to get out of trees and in broken limbs when the animals fall. Sernylan (phencyclidine hydrochloride) has been successfully used, but has been removed from the commercial market.2 The lack of mortality during this capture event suggests a wide safety margin for Telazol® in this species. The most notable precautions that should be taken in its use include: proper dart placement, careful selection of the areas in which animals are darted, and special care to avoid darting juvenile or infant animals with adult dosages.


We thank Dr. Marco Herrero and Dr. Mo Salman for support and assistance for this project. We thank participating students for their excellence in animal care and for assisting with animal monitoring and handling.

Literature Cited

1.  Agoramoorthy, G. and R. Rudran. 1994. Field application of Telazol® (tiletamine hydrochloride and zolazepam hydrochloride) to immobilize wild red howler monkeys (Alouatta seniculus) in Venezuela. J. Wildl. Dis. 30: 417–420.

2.  Glander, K.E., L.M. Fedigan, L. Fedigan, and C. Chapman. 1991. Field methods for capture and measurement of three monkey species in Costa Rica. Folia Primatol. 57: 70–82.

3.  Karesh, W.B., R.B. Wallace, R.L.E. Painter, D. Rumiz, W.E. Braselton, E.S. Direnfeld, and H. Puche. 1998. Immobilization and health assessment of free-ranging black spider monkeys (Ateles paniscus chamek). Am. J. Primatol. 44: 107–123.

4.  Schobert, E. 1987. Telazol® use in wild and exotic animals. Vet. Med. 1082–1088.

5.  Vie J.C., B. Moreau, B. de Thoisy, P. Fournier, and C. Genty. 1998. Hematology and serum biochemistry values of free-ranging red howler monkeys (Alouatta seniculus) from French Guiana. J. Zoo Wildl. Med. 29: 142–149.


Speaker Information
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R. Scott Larsen, DVM
College of Veterinary Medicine and Biomedical Sciences
Colorado State University
Fort Collins, CO, USA

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