Lost manhood

THE skewed sex ratio is not confined to Katerniaghat (see box Bad numbers). Project Crocodile has been conspicous in giving the cold shoulder to the male gharial. Shrinking and fragmented habitat have increased competition among the males. "The social structure and behaviour of gharials is such that adult males try to push away sub-adults," says Choudhary.

There are other reasons for the lopsided sex ratio. All crocodile species, including gharials, belong to a group of reptiles whose sex is determined by environmental temperatures and not just heritable chromosomes, according to a study by D C Deeming, published in Biological Sciences (Vol 322, No. 1208, December 1, 1988). Embryos need an optimum temperature of 32c to emerge as males, according to Demming.

Lower or higher temperatures mean the embryos turn out to be females.In natural conditions when variations in temperature are much less, there is some balance in the sex ratio. Gharials are endothermic -- they regulate temperatures by external means. They are active at night and relatively inactive during the day. As rivers warm slowly in the morning, gharials bask on sand banks. At night, the river cools slowly, so the gharials remain submerged. Sand mining and fluctuations in water-levels upset this behaviour, affecting breeding habits and, therefore, the sex ratio.

Demming's study indicates that conservation programmes based on egg collection and incubation also upset breeding habits and can hasten the decline of natural populations.