SURVIVORSHIP, DISPERSAL AND SEX-RATIOS OF ZEBRA FINCHES TAENIOPYGIA-GUTTATA IN SOUTHEAST AUSTRALIA

Membership of three permanent breeding colonies of Zebra Finches Taeniopygia guttata studied in farmland changed continually due to arrival and departure of birds from distant colonies. Sixty-six percent of adults stayed for less than 1 month, and many that stayed longer disappeared for extended periods. Over 78% of adults captured were hatched in other colonies and only 23% made a breeding attempt in their natal colony. There was no sex-biased natal dispersal or philopatry, but there were sex differences in the timing of dispersal. Sex ratios at the end of parental care were variable and may depend on food resources. Adult ratios were slightly male-biased. Annual losses of adults ranged from 72 to 82% across colonies, but mortalities and dispersal were heavily confounded by high adult mobility. The oldest bird was more than 5 years old. A total of 67% of young were lost between fledging and nutritional independence at 35 days of age, and only 20% of fledglings survived to day 80, the age of first breeding. Artificial supplies of seed at baited walk-in traps prolonged the stay of dispersing adults from other colonies, enhanced the survivorship of young hatched in the colony and possibly affected the secondary sex ratio. In this southeast part of their Australia-wide distribution, Zebra Finch populations appear to be highly mobile over a very large home range with extensive free interchange of members among a number of permanent breeding colonies. High mobility may be adaptive for exploiting patches of seed and water in a highly erratic environment.