pinnae unfurl at about 1 week, but ear canals remain closed until 25–28 days. Pelage develops uniformly from about 2 weeks and the nestling coat is replaced by seasonal coat at 13–16 weeks. Lower incisors erupt at 21 days, upper incisors at 28–35 days and molars about 6–7 weeks. Full growth is reached at about 6 months (Barkalow & Shorten 1973; Tittensor 1977).
Both species may become reproductively mature at about the same age (see above) and both produce about the same number of young per year. Older females produce more litters annually than do yearlings, but generally, fecundity depends on the availability of food and comfortable climatic conditions during the breeding season.
Mortality among juvenile Palm Squirrels in Perth was about 30% (Wright 1972). The species is not long-lived, Chaudry & Beg (1977) reported longevity of up to 18 months in the wild in India, but suggested it could be longer. No information on the Australian population is available.
Grey Squirrels have been kept captive for up to 20 years, but survival in the wild being low (less than 25%) during the first year, their life expectancy is only about 1 year. If young animals survive beyond this, they frequently live much longer, most as long as 7–8 years, a survival rate of greater than 52%. Barkalow, Hamilton & Soots (1970) derived a longevity of 9 years for free-living individuals. A captive Grey Squirrel at Ballarat (Victoria) lived for longer than 13 years (Seebeck 1984). Adult females have a slightly higher survival rate than adult males. Barkalow et al. (1970) calculated that cohort longevity was 6.4 years based on a 99.5% turnover in the population. No information is available for the Australian population.
In India and Pakistan, the Palm Squirrel is a common and widespread commensal, found in homes, gardens and roadside trees. It is completely diurnal and generally arboreal. In particularly arid parts of its range, thick foliage and the moist microclimate of trees, particularly in orchards, provide shelter from excessive climatic conditions (Ghosh 1975). Prakash (1975) found it to be uncommon in the desert biome of north-west India where it was found most frequently in rocky and ruderal areas.
It has not adapted to natural environments in Australia, and is restricted to suburban and/or plantation areas close to the original release sites. In Perth, the population still occupies an area of only about 30 km2; in Sydney the area occupied was smaller. Palm Squirrels shelter in introduced trees or buildings and the population is limited by‘natural’ food availability. At Como High School, Perth, the population decreased during school vacations when additional food was unavailable (Scanlan et al. 1978). Wright (1972) found that the population density was greatest in areas of Perth Zoo that had the highest density of fruiting and nest trees, and that were closest to a supply of supplementary food. From this, she inferred that these were major limiting factors in the spread of the species in Perth. The Perth Zoo population was estimated to consist of about 1000 animals (Wright 1972).
Prakash et al. (1968) found that in India home ranges were overlapping for both sexes – about 0.2 ha for males, and about 0.15 ha for females. Wright (1972) determined the home ranges (both sexes combined) in Perth Zoo of between 0.02 and 0.26 ha. Observed range length in India was 60–70 m for males,