Document ID: chunk:federal_register_of_legislation:F2007B00386:body:0:p10
Version: federal_register_of_legislation:F2007B00386
Segment Type: other
Provision Reference: 
Character Range: 24566–27586

Rehabilitation priorities are primarily determined to protect Abbott's Booby sites, although other threatened species are also considered in determining the priority of sites. A significant additional result of CIRRP will be the reestablishment of habitat that supports other species such as the goshawk.

Natural Catastrophes
Although goshawks, as generalist raptors, are likely to cope well with habitat modifying natural catastrophes, the effect of events such as cyclones are more severe on small populations. There is a possibility of an increase in severe storms and cyclones occurring as a result of Greenhouse gas-induced climate change. It would be useful to understand the effects of cyclones and severe storms on goshawk populations to help predict the impact of any increases.

Small population size
The risk of extinction varies inversely with population size (Lacy 1987) due primarily to demographic and environmental variability the effects of which can become marked in small populations. Demographic variability is the individual variation in reproductive success, which is masked when population size is large. Very small populations (< 30 individuals) can easily become extinct as a result of random demographic variation between individuals (Caughley & Sinclair 1994).

The reproductive success of a population is also likely to vary with fluctuations in the environment. The degree of this fluctuation is determined by how much seasonal and annual variation in habitat quality there is. The influence of this on the risk of extinction increases markedly with decreasing population size. For example, a cyclone, an extreme example of environmental variation, causing the death of half the population of 10000 animals has an insignificant affect on the probability of extinction of that population. However, if half a population of 200 animals dies, the risk of extinction of that population increases significantly (Caughley & Sinclair 1994).

Inbreeding Depression
The risks of inbreeding depression increases with decreasing population size due to the increase in frequency of homozygous alleles. Populations at risk of inbreeding depression are probably a couple of dozen individuals or smaller in size which have been at that size for several generations, as a population contraction must last for several generations to lead to a significant loss of heterozygosity (Caughley & Sinclair 1994). Any action on the island which might permanently, rather than temporarily, reduce the number of mature individual Christmas Island Goshawks (such as permanent forest clearance rather than temporary storm damage) would raise the possibility of inbreeding depression as a concern in their conservation.

Other Potential Threats
Killing of Christmas Island Goshawks, especially by poultry owners, has been considered to be a significant threat to goshawks in the past (Stokes 1988). Given the small population size, any killing of either juveniles or adult Christmas Island Goshawks would be considered a