Courtship and mating of Palm Squirrels involves chasing and tail-biting a single female by several males, together with male-male fighting. A female waits, calling, until the victorious male chases her before overpowering, mounting and mating; this occupies 10–20 minutes. Females are submissive during mating although twining of tails may occur and biting by the female may end matings. Females will mate three to four times during the day with the same or different males. Breeding is seasonal in India from February to September with peaks in April and September. Males are reproductively quiescent between November and January. Gestation lasts about 42 days, and one to five young, usually two to three, are born in a grass and fibre nest usually placed in a tree, wall or roof. Weaning takes place at about 10 weeks and sexual maturity is reached at 8–9 months. Mature females may have two litters per year. Sex ratio at birth is about 1:1, but in India female mortality is higher and the adult sex ratio is 2.3:1 (Purohit et al. 1966; Prasad et al. 1966; Chaudry & Beg 1977). In Australia, the species breeds between August and May, with peaks in October and April. The recorded sex ratio for Palm Squirrels at Perth Zoo was 1:1 except during May, when no adult males were trapped. Litter size averaged 2.5. Nests (of palm fibre, jute sacking, grass or wool) were placed in Phoenix, Melia, Agonis, Pandanus trees or in clumps of bamboo (Wright 1972).
Grey Squirrel courtship and mating is also polygamous and involves chasing and display. Breeding is seasonal, the species breeding in North America during spring and summer. Males are reproductively quiescent in autumn, but may be fecund all year in England. Females are polyoestrus, display no post-partum oestrus and are anoestrus between September and December. The length of the breeding season depends on food availability and climatic conditions. In Australia, breeding was reported during late spring-late summer (October to February). Gestation lasts 42–45 days and one to nine young, usually three to four, are born in an untidy twig and leaf nest (drey) lined with soft fibre and usually built in a tree fork. If disturbed, females may transport young by carrying them in the mouth. Weaning occurs between 7 and 10 weeks and sexual maturity is usually at 10–12 months, although precocious breeding has been reported (one female in the United States gave birth at 168 days – less than 6 months old). Mature females in the Northern Hemisphere may have two litters per year, yearlings only one. Sex ratio of nestlings was 1.1:1, but for adults it was 0.85:1 (Barkalow & Shorten 1973). Two to three litters per year were reported for the Australian population (Watts & Aslin 1981).
Embryology and Development
Newborn Palm Squirrels are naked and pink, although incipient dorsal markings are visible. Vibrissae are present, eyes are closed and the pinnae are folded. Measurements are about 50 mm head & body, tail about 30 mm, pes about 12.5 mm and weight 5–8 grams. Young vocalise within a week of birth and are capable of uncoordinated movement. Their eyes open at 15–25 days and pinnae unfurl at 7–10 days. The pelage develops uniformly, with dorsal stripes becoming prominent in the second week and mature colouration attained in 8– 10 weeks. Teeth are not visible in newborn young, but lower incisors may be visible in young a week old. Upper incisors usually erupt later and adult dentition is complete at 12–13 weeks. More than 70% of growth of young occurs in the first 8 weeks after birth. A hand-reared litter in Perth (Scanlan et al. 1978) appeared to follow the general growth trends described by Purohit et al. (1966), but Wright (1972) found that wild-caught young in Australia at 4–5 weeks old were almost twice the weight reported by Purohit et al. (1966) for Indian animals.
Grey Squirrels are also born naked and pink, with vibrissae visible, eyes closed and ears furled. Total length is about 115 mm and weight 13–17 grams. They can vocalise within hours of birth. Their eyes open at about 28–35 days and