Document ID: chunk:federal_register_of_legislation:F2007B00392:body:0:p12
Version: federal_register_of_legislation:F2007B00392
Segment Type: other
Provision Reference: 
Character Range: 29321–32112

are very difficult to catch and sensitive to handling (T. Stokes pers. comm.) and a censusing method will probably involve attempting to count the number of breeding attempts initiated in a particular year. Alternative methods of censusing Christmas Island Frigatebirds need to be evaluated due to the expense of repeating ground-based censuses of the number of nesting birds. Frigatebirds are prone to desertion of their nests and aerial surveys by conventional aircraft should not be considered (T. Stokes pers. comm.). However it may now be practical to develop an aerial census technique using remote-controlled helicopters, which are large enough to carry video or still-camera equipment. The budget provides for the hire of such a helicopter to be used with camera equipment already possessed by the PAN Christmas Island office.

              Action:  2. Monitor the total breeding population size.
In order to estimate the size of the breeding population it is essential to monitor the number of pairs which commence breeding each year. Due to the time lag between a breeding attempt and a new breeder entering the population, a decrease in the number of breeding adults will not result in a change in the number of breeding-age adults for at least 10 years and probably longer. There appears to have been a significant loss of breeding habitat in the recent past, so the number of breeding adults may be significantly lower than the number of breeding-age adults. Two surveys should be carried out to determine the status of this species and whether management action is required in the future. Repeated surveys of the number of breeding-age adults will indicate whether the breeding population is currently declining; repeated surveys of the number of breeding adults may indicate whether the population will decline in the future. A survey at the time when frigatebirds are beginning to pair would probably give the best indication of the total population of breeding-age adults. A survey of the number of pairs which begin nesting would also help to determine whether the population is restricted by lack of suitable breeding habitat.

An initial pair of surveys of the whole breeding population should determine its size and distribution. The results of these surveys can then be used to assess whether more intense monitoring of the population is required. There are no guidelines as to the length of time between surveys but counts every five to ten years have been used to monitor some other endangered species (Green & Hirons 1991); given the lifespan of this species, population-wide surveys every 10 years may be sufficient. If the initial paired survey indicates that the number of breeding adults is not significantly less than the number of breeding age adults then the