• Madhav Gadgil

      Articles written in Proceedings – Animal Sciences

    • Observations on the natural history and population ecology of the social waspRopalidia marginata (Lep.) from Peninsular India (Hymenoptera: Vespidae)

      Raghavendra Gadagkar Madhav Gadgil N V Joshi A S Mahabal

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      Ropalidia marginata, the most common Indian social wasp, belongs to a crucial stage of social evolution showing no obvious morphological caste differentiation but a behavioural caste differentiation and a dominance hierarchy that appears to influence division of labour. The nests consist of a single open comb that can sometimes have up to 500 cells and 10 pedicels. Nests are initiated and abandoned all round the year. Initiation is by 1–20 foundresses, 1–4 being the most common number. There is a great deal of variation in brood developmental times both within and between nests. Male progeny disappear from the nest soon after emergence while daughters stay on at the parent nest for a mean period of about a month. Small nests have a single egg layer while large nests have two or more females with well developed ovaries that presumably lay eggs. Most nests are short-lived, small nests being highly susceptible to failure. Large nests are less susceptible to failure but the emergence of multiple egg layers reduces the average relatedness of workers to the brood which presumably is the cause for large scale emigrations from these nests. An interaction of ecological and soical factors therefore appears to determine the growth of a nest.

    • Observations on the social behaviour of free ranging groups of tame Asiatic elephant (Elephas maximus Linn)

      Madhav Gadgil P Vijayakumaran Nair

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      This study is based on 645 hr of observations on the social behaviour of tame elephants maintained at three wildlife sanctuaries of Bandipur, Mudumalai and Anaimalai in South India. These elephants are wild captured adults, and their calves born in captivity. The observations were carried out when the elephants are left free for grazing in their natural habitat, where they often intermingle with wild herds. The adult females always stay together when there are calves present: while the adult males graze by themselves. The calves position themselves between adult females and juveniles closer to their mother. All females rush together when a calf sounds alarm. The adult females stand guard over calves lying down for rest thereby accepting considerable reduction in the amount of time devoted to feeding. The ‘allomothers’ suckle other calves when they have no calf of their own, sometimes as much as the mother herself. The acts of social communication are largely initiated by the calf touching the breast or body of an adult female with its nostril. There is much variation in the extent of communication and suckling from one allomother to another with a mother definitely preferring her own calf.

    • Foreword

      Madhav Gadgil

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    • On the communication of well-being

      Madhav Gadgil Malati Hegde N V Joshi Sulochana Gadgil

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      The form that any communicatory exchange takes would depend on the extent to which the interests of the signaller and the recipient are at variance. Where such interests coincide, i.e. in cases of mutualism, the signals may be conspicuous when an immediate response is favoured, but rather subtle and variable otherwise. Over 80 % of the events of tactile communication that we have noted in our study of the social behaviour of free ranging groups of tame elephants appear to belong to this latter category. On Smith’s standard classification, they can only be classified as ‘associative’, related to remaining in the company of another individual. However, such signals are commoner by a factor of 20–100 amongst elephant calves and their mothers and allomothers when compared to exchanges between adult cows. We suggest that the function of these signals is mutual monitoring of the state of well being amongst related individuals. The considerable degree of altruistic behaviour displayed in social groups, such as those of elephants is now believed to subserve the function of enhancing the inclusive fitness of the individuals concerned. We explore a mathematical model of exchange of social aid which suggests that animals in social groups may enhance their inclusive fitness further by adjusting the amount of social aid exchanged in relation to the state of well being of the donor as well as the recipient. Our model further suggests that optimal social aid depends on the state of well being in a complex fashion making it difficult for the recipient to deceive the donor so as to extract more aid. We therefore expect that by and large honest communication of the state of well being would be characteristic of the higher social animals. Such communication would be based on normal physiological changes consequent on a change in well being. Thus animals with a superior degree of well being would take postures conducive to greater activity, would be more receptive to sensory inputs and may also shift the balance of production of various metabolites. This monitoring of the well being has greatly advanced in the human species and may be at the base of the elaborate health care amongst human societies.

    • Birds of the man-made ecosystems: the plantations

      R J Ranjit Daniels Malati Hegde Madhav Gadgil

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      One-hectare plots were sampled for bird species diversity in the Uttara Kannada district. These plots represented well-preserved evergreen/semievergreen forests, secondary/moist deciduous forests showing different levels of degradation by man and plantations of teak, eucalypts and betelnut. It was found that the betelnut plantation and the evergreen/semievergreen forests had the least bird species diversity ofH′ = 2.58 and 2.61 respectively. The eucalypt and teak plantations hadH′ = 2.69 and 2-92 respectively. In the secondary/moist deciduous forests it ranged from 2.80–3.39. Despite the apparent increase in diversity in the man-modified vegetation types, it was found that there was a gradual displacement of the bird species composition from what was typical to the evergreen forests to those of more urban and scrubby habitats in these man-modified vegetation types. This was particularly so in the eucalypt plantation.

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