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Ozark - the Australian Wildlife Carer's Information & Communications Network

Sun - Apr 30
2017

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CHRISTMAS ISLAND GOSHAWK

By Michelle Manhal

Method

In 2000 the Christmas Island Goshawk met the criteria as being Critically Endangered. To determine the size of the Island's Goshawk population and the ecological requirements for this species, a mark-recapture (banding) was seen as the first stage of this expedition. During the month long expedition 52 Christmas Island Goshawks where trapped and colour banded.

Two active nests were discovered during this study. Both were in Macaranga trees near the edge of made (single lane roads) in primary rainforest. The last time there was a discovery of a nest site or its description for this species was in 1940.

The information we received from Parks Australia North Christmas Island when arriving on the Island, was that the CI (Christmas Island) Goshawk was easy to find.

It was apparently a simple matter of driving around, stopping from time to time and opening your car door and waiting. The CI Goshawk would apparently just come and land on the door of your car, as they are a curious species, not like the Brown Goshawk accipiter fasciatus. Despite these assurances we found this species a little less curious than first described.

Robber Crab - Photo by Michelle Manhal
Robber Crab   Birgus latro
Photos by Michelle Manhal

The expedition team had 2 vehicles at their disposal to which the survey effort was divided between 2 survey teams for 10 hours per day. This allowed 30 survey days per team and 2 teams operating simultaneously for the duration of the expedition gives c. 600 search hours.

Moult Data

Data on moult and plumage condition was collected in two ways. A moult score was recorded for each Goshawk and digital images were taken of most birds following banding and prior to release. A three point scoring system was used for each of the following wing feathers: primaries 1-10, secondaries, 1-10, tertiaries 1-4 and tail feathers 1-6. Each feather was scored on one side of the body only and that was the right side; M for feather missing; N for a new feather or growing feather; and O for an old or worn feather. Head and body feather tracts were scored simply by presence or absence of growing pin feathers. A score of 'Y' for 'yes in moult' or 'N' for 'not in moult' was recorded for crown moult and separately for body moult.

Normally one photo of the under wing opened and body, one of back with wing opened and a head photo either front-on or from the side. Photographs were taken to illustrate, patterns of moult. Age specific plumage and soft part colouration and iris colour.

Juvenile CI Goshawk - Photo by Michelle Manhal
Juvenile CI Goshawk
2nd year CI Goshawk - Photo by Michelle Manhal
2nd year CI Goshawk
Adult CI Goshawk - Photo by Michelle Manhal
Adult CI Goshawk
2nd year CI Goshawk - Photo by Michelle Manhal
2nd year CI Goshawk
Juvenile CI Goshawk - Photo by Michelle Manhal
Juvenile CI Goshawk
Photos by Michelle Manhal

The active survey and trapping effort was evenly divided between morning and afternoon on most days. With approximately 5 hours being spent in each half of each day by all survey teams we note that 66% of males were trapped in the afternoon contrasting with 68% of females being trapped in the morning.

Habitat

Habitat has decreased by 25% and Goshawks are competing with another diurnal raptor, the Australian Kestrel Falco cenchroides which benefits from past rainforest clearing. Goshawks and Kestrels will be competing for those small vertebrate prey species remaining. Especially those restricted small mammal and reptile species venturing out into more open areas. The impacts of the Yellow Crazy Ant are also locally reducing prey abundance and diversity particularly at the sight of the multi queened super colonies. Even several years after eradication of the Yellow Crazy Ants from these areas, large areas of rainforest continue to be greatly affected with vegetation diversity and structural changes and a persistent reduction in the vertebrate and invertebrate biodiversity in these areas. Surveys in some of theses areas failed to detect a single Goshawk.

Before Yellow Crazy Ants - Photo by Michelle Manhal
Before Yellow Crazy Ants
After Yellow Crazy Ants - Photo by Michelle Manhal
After Yellow Crazy Ants
Photos by Michelle Manhal
Recommendations

A similarly designed and conducted study a year later will consolidate our understanding of the ecological requirements of this endangered species. Especially in these key areas: Cohort survivorship; population age structure; population size; pair, site and territory fidelity; and gain a more comprehensive data set on the diet especially as it relates to age and sex of Goshawks. Most importantly of all an estimate of the population size should be possible following a successful second survey. An education campaign to encourage both reports of sightings of Goshawks and to foster an appreciation of this endemic species may reduce some of these threats.

Christmas Island -  Photo by Michelle Manhal
Christmas Island
Photo by Michelle Manhal





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