The Tenrecs: A Study in Mammalian Behavior and Evolution by J. F. Eisenberg & Edwin Gould, pp. 1-7.
published in Smithsonian Contributions to Zoology No. 27 (1970)
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| J. F. Eisenberg and Edwin Gould |
The Tenrecs: A Study in Mammalian Behavior and Evolution |
Introduction
The tenrecs are a diversified family of insectivorous mammals confined to the island of Madagascar. Including some 25 named forms divisible into 7 genera, these animals offer a unique opportunity for the study of behavioral evolution. They occur within a wide range of habitats and have adapted to aquatic, fossorial, and semi-arboreal ecological niches. Nowhere else have the insectivores displayed such a range of adaptation within such a limited geographical region. Although the tenrecs have exhibited a remarkable adaptive radiation on Madagascar, this has been accomplished with few major alterations in basic body plan; thus, we have in essence a mammal with many conservative physiological and morphological features including: an unstable thermoregulation, reduced visual capacity with concomitant dependence on auditory and chemical modes of communication, retention of the testes within the body cavity of the male, retention of the cloaca and retention of the conservative reproductive trait which involves the production of rather large litters of altricial young. With the tenrecs, then, we are presented with an opportunity to examine many of the current limits of adaptation developed by primitive Eutherian mammals.
On Madagascar, the insectivores reach their greatest size in the form of Tenrec ecaudatus. The streaked tenrec, Hemicentetes semispinosus, has evolved the most complex communications system and social grouping tendencies of any insectivore. Elaborate anti-predator mechanisms have been developed permitting many tenrec species to compete successfully with viverrid carnivores and, thus, they prevail not as the dull-colored, small, cryptic mammals recognized as insectivores by naturalists in the temperate zone, but in many cases as large or conspicuously colored mammals (see Figures 1 and 2).
In 1963 Edwin Gould went to Madagascar to study the echolocating ability of tenrecoid insectivores and, as a result, became involved with the total biology of these animals. On his return, he brought many captive specimens with him and joined forces with John F. Eisenberg, who had initiated captive studies on the behavior of selected species of hedgehogs, shrew, and the hedgehog tenrec, Setifer.
In 1966 and 1967, Eisenberg and Gould returned to Madagascar to develop a more comprehensive field study on the behavior of the streaked tenrec, Hemicentetes, as well as the other genera. Preliminary results of these studies have been published in various journals (Eisenberg and Gould, 1966 and 1967; Eisenberg and Muckenhirn, 1968; Gould and Eisenberg, 1966; Gould, 1965).
ACKNOWLEDGEMENTS
Our research was supported by grants from the National Science Foundation and the United States Air Force.1 Throughout the course of our captive studies, facilities and support were generously extended by the National Zoological Park-Smithsonian Institution. We gratefully acknowledge the assistance rendered by Drs. C. Handley and H. Setzer who allowed us to utilize the collection of the Tenrecidae at the United States National Museum. Dr. G. Corbet kindly assisted us and permitted examination of the Madagascar collection in the British Museum.
During the three year course of our study on the Tenrecidae of Madagascar, a number of individuals at the National Zoological Park contributed their time and energy to the elucidation of some difficult problems. A. Underhill and B. Myton spent considerable time in the measurement of thermoregulation in the captive tenrec colony. M. Linnet studied the learning ability of Microgale talazaci in a T-maze and J. McAulay conducted a number of climbing tests in an open field arena with all three species of captive Microgale. Miss N. Muckenhirn aided the project tremendously by hand-rearing both Setifer setosus and Tenrec ecaudatus. In addition, she submitted some rather excellent recordings of vocalizations from all of the Tenrecidae.
Mr. E. Maliniak, senior keeper at the National Zoological Park, was responsible for the captive maintenance of the colony. Mr. Maliniak kept excellent records concerning breeding, growth, and weight changes throughout the annual cycle. Our breeding success in captivity is in large measure due to his care and consideration. Miss G. Schuler lent her sensitive talents and was able to draw Figures 25, 29, 59, 60, 62, and 74 for this publication. Mr. A. Miller assisted in the 1966 expedition. During 1967, Mr. T. Schneider assisted in the field work in Madagascar. Drs. Charles Berlin and Richard Chase gave valuable advice and assistance on analysis and recording of tenrec sounds. Data recording and assistance during experiments was ably rendered during the 1966 field work by Mrs. E. Eisenberg. Mrs. W. Holden was responsible for the final preparation of the manuscript for publication. Both authors are indebted to Mrs. E. Eisenberg for her efforts in reading every word of the manuscript and offering criticism concerning our style and clarity of expression. To all of these people we are extremely indebted.
Throughout our various sojourns on Madagascar, we received excellent cooperation from both the Institut Pasteur de Madagascar and the Institut Recherches Scientifique de Madagascar. In particular, we extend our thanks respectively to the two directors, Dr. E. R. Brygoo and Monsieur Roederer. Dr. Brygoo kindly examined tenrecs for parasites and made the information available to us. The Institut Pasteur was our primary laboratory headquarters in Tananarive. We are also indebted to Dr. Dodin, Assitant Director of the Institut Pasteur for his help.
Without the excellent cooperation and hospitality from the Department of Eaux et Forêts the entire project would have been impossible. We are particularly indebted to them for use of a headquarters building at the forestry camp in Perinet. To M. Jean Jacques Natai, Ministre de l'Agriculture; M. Georges Ramanantsoavina, Director des Eaux et Forêts et de la Conservation des Sols; M. Henri Andriantsiferana, Directeur-Adjoint des Eaux et Forêts et de la Conservation des Sols; M. Guy Ramanantsoa, Ingénieur Principal des Eaux et Forêts, Chef de la Division des Réserves Naturelles, des Parcs Nationaux; and M. Ferreol Rakoto, Agent Technique des Eaux et Forêts; we extend our deepest appreciation.
The following report is a summary of two years field work in Madagascar coupled with the data collected at the National Zoological Park with our rather extensive captive colony.
The following abbreviations are used throughout the text: USNM (United States National Museum) and BM (British Museum (Natural History)).
ITINERARIES AND FIELD METHODS IN MADAGASCAR
The major portion of our field work on Madagascar has been conducted in the central and eastern regions. We have concentrated our efforts in two different habitat types; first, the eastern tropical evergreen rainforests in the vicinity of Ranomafana and Perinet; secondly, in the plateau ecotone area immediately adjacent to the two rainforest areas. This would include the plateau region from Fianarantsoa to Alakamisy Ambohimaha and Ahimahasoa and the area in the vicinity of Lake Alaotra.
In addition, Gould surveyed the drier western habitats in 1963 and in 1967. During his first visit, Gould traveled by automobile from Ambositra to Morondava south to Tulear and back to Fianarantsoa. In 1967 Gould made a special trip to the Antsingy region in the northwest. The map in Figure 3 outlines the itineraries and also indicates the chief vegetational zones on the island of Madagascar. As can be seen, our work permits us to make generalizations about the insectivores of the eastern rainforests and their plateau relatives. In addition, some comments can be made concerning the insectivore fauna and its adaptive syndrome in the more arid west.2
Field methods were conducted according to a classical pattern. Habitats were surveyed on foot. Some plant samples and soil samples were taken at each major collection site and extensive live trapping was executed to determine the mammalian species-composition. Routine collection sites were established and, by sampling and releasing specimens over a 3-month period which were then followed up in 1967, we were able to make estimates of population density, longevity, and population structure for at least two species of tenrecs. Most tenrecs were collected by digging them out of their burrows. At the time that an active burrow was discovered the immediate area was photographed. As the burrow was excavated the dimensions were noted and recordings of the temperature of the burrow itself, the environmental temperature, and the animal's body temperature were often taken. This enabled us to formulate a description of the micro-environment for several tenrec species.
Observations were made in the field during the day and the night. At night observations were made with head lamps or with infrared viewing devices; these included both wide angle and telephoto devices for 6 to 100 feet observation with both rechargable battery operated light sources as well as 12 volt storage battery operated seal beam lights. Since the tenrecs were so cryptic, it became necessary to supplement field observational techniques with captive, seminatural conditions by employing large outdoor enclosures. The most elaborate observation cage constructed was located at Perinet. An area of second growth natural vegetation, approximately 85 feet by 66 feet, was completely fenced in. By means of overhead platforms, animals which were placed in this seminatural habitat could be observed very effectively with infrared illumination (see Figures 4 and 5). As a result of the field techniques and seminatural observation procedures, we obtained reasonable data concerning activity periods, food preferences, location of feeding and denning sites, and grouping tendencies.
To aid in our understanding of the ecology of the Tenrecidae, it was necessary to consider predation. By an examination of owl pellets and various "sign" in the environment, we formulated certain hypotheses concerning predation by boas, owls, and viverrid carnivores. To supplement these observations, boas and civets were kept in captivity and utilized in predator tests. These tests were conducted in a room measuring approximately 10 feet by 20 feet where the predator could be allowed to run at semiliberty before various tenrecs weren introduced in.
In captivity, the colony was routinely weighed and measured, giving some indication of growth potential. Rather accurate records were maintained at one period to determine food consumption for the various age and sex classes. Staged encounters between the various age and sex classes for any given species of tenrec were run according to a methodology developed by Eisenberg (1963, 1964 a, b). Such encounters permitted a description of the fundamental behavior patterns employed in social situations, including courtship and agonistic behavior. Captive breeding in Madagascar was carried out with most of the tenrec species belonging to the subfamily Tenrecinae. These data enabled us to calculate such basic information as gestation period and, in addition, allowed us to supplement our behavioral studies with observations on parental care, ontogenesis of behavior, and the break-up of the family group.
At the National Zoological Park, additional records were kept on the captive colony enabling us to study such long term phenomena as growth and seasonal torpor with all concomitant weight changes and alterations of activity pattern. In addition, a breeding program was carried out at the National Zoological Park which netted us valuable data on gestation, maturation rates, and growth. During the summer of 1966, the thermoregulatory ability of the tenrecs was also studied in some detail.
The bulk of our experimental work in Madagascar involved the analysis of communication by means of the stridulating organ found in the juvenile Tenrec ecaudatus and in the juvenile and adult of both species of Hemicentetes. By direct observation of the animals under seminatural conditions, it was possible to define those circumstances under which stridulation took place. To refine our observations, we attempted to correlate the type of stridulation with a given motivational state displayed by the animal in question. For this reason, tenrecs of the genus Hemicentetes were subjected to varying alterations in the ambient environment by conditioning them to either a constant amount of light or a constant sound volume and then suddenly changing the intensity of the stimulus input. By this means, the animals were induced to adopt varying degrees of spinal erection and concomitant arousal. In conjunction with these observations, we were able to monitor the stridulating response of the animals and formulate an hypothesis concerning the form of stridulation as a function of arousal. Once we could correlate stridulation type with overt behavior, it was possible to classify the sound types and assign the varying sound types with a given motivational state. With such basic information, it was possible to design experiments which would elucidate the communicatory significance of stridulation to other members of a Hemicentetes group.
The sound produced by the stridulating organ has the greatest energy concentration from 20,000 to 30,000 cycles per second. For this reason, rather elaborate recording equipment had to be employed. Figure 6 illustrates the recording and playback hook-up utilized in our experiments. Further details of procedure and results will be given in the sections to follow.
The Tenrecs: A Study in Mammalian Behavior and Evolution by J. F. Eisenberg & Edwin Gould, pp. 1-7.
published in Smithsonian Contributions to Zoology No. 27 (1970)
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