Factors influencing seasonal and monthly changes in the group size of chital or axis deer in southern India.
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Date
1997-03
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Abstract
Chital or axis deer (Axis axis) form fluid groups that change in size temporally and in
relation to habitat. Predictions of hypotheses relating animal density, rainfall, habitat structure,
and breeding seasonality, to changes in chital group size were assessed simultaneously using
multiple regression models of monthly data collected over a 2 yr period in Guindy National Park,
in southern India. Over 2,700 detections of chital groups were made during four seasons in three
habitats (forest, scrubland and grassland). In scrubland and grassland, chital group size was
positively related to animal density, which increased with rainfall. This suggests that in these
habitats, chital density increases in relation to food availability, and group sizes increase due to
higher encounter rate and fusion of groups. The density of chital in forest was inversely related to
rainfall, but positively to the number of fruiting tree species and availability of fallen litter, their
forage in this habitat. There was little change in mean group size in the forest, although chital
density more than doubled during the dry season and summer. Dispersion of food items or the
closed nature of the forest may preclude formation of larger groups. At low densities, group sizes
in all three habitats were similar. Group sizes increased with chital density in scrubland and
grassland, but more rapidly in the latter–leading to a positive relationship between openness and
mean group size at higher densities. It is not clear, however, that this relationship is solely because
of the influence of habitat structure. The rutting index (monthly percentage of adult males in hard
antler) was positively related to mean group size in forest and scrubland, probably reflecting the
increase in group size due to solitary males joining with females during the rut. The fission-fusion
system of group formation in chital is thus interactively influenced by several factors. Aspects
that need further study, such as interannual variability, are highlighted.
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Keywords
Grouping behaviour, Axis axis, population density, rainfall, tropical dry evergreen, forest, scrubland, grassland, seasonality
Citation
Raman T R Shankar. Factors influencing seasonal and monthly changes in the group size of chital or axis deer in southern India. Journal of Biosciences. 1997 Mar; 22(2): 203-218.