Kangaroo Island Glossy Black-Cockatoo Foraged Sheoak Data, 2023 – 2024

Brief description

Notes

Lineage

Sampling methods

We estimated foraging intensity per patch at a total of 54 remnant and revegetated A. verticillata feeding habitat sites over three time periods in 2023-24, comparing sites in regions with greater than 50% and less than 50% fire affected habitat. We also collected cones from 391 foraged trees at 39 of these sites to determine Clout’s Index, a measure of food profitability, and modelled the results for a range of environmental variables. Sample site characteristics are summarised in Table 1(a) and 1(b).

Table 1(a). Sample sites, Foraging intensity: 54 sites in total, some sites repeat surveyed

Table 1(b). Sample sites, Clout’s Index of foraged trees: 39 sites in total

Foraging intensity surveys were carried out once during the 2023 and 2024 nesting seasons (February-June), and once in 2023 post-breeding period (September-November), when Glossy Black Cockatoos had grouped together in flock regions. Habitat searches were undertaken at the beginning of the study to locate foraging sites within known feeding habitat patches. Transect surveys were conducted within the habitat patches, both at sites where cones were being collected for Clout’s Index analysis and at additional sites where foraging sign had been observed. We aimed to maximise the area surveyed, with starting points located where feeding sign was first encountered in the habitat. Female trees were categorised as either ‘foraged’ if chewings were present under the tree or ‘not foraged’ if no chewings were present. Chewings weather and change colour with age, with three age groups recorded: up to a few weeks old (cream to bright orange, 32%), darker to faded orange (65%), indicating feeding within the last few months, and older pale brown chewings (3%). Foraging intensity for each site was calculated as the proportion of foraged trees relative to the total number of female trees in the transect.

Two slightly different methods were employed, both variations of walking transects (Pepper 1997). Both methods aimed to record the feeding status for a minimum of n=50 female trees, although this was not possible in some small revegetation sites. Dead trees or trees with less than 75% healthy foliage were not sampled. For surveys conducted during the 2023 Glossy Black Cockatoo breeding season, every live female tree encountered with more than 20 russet cones was noted and its feeding status recorded. In the subsequent two sampling periods, transects aimed to cover most or all of a habitat patch so that a representative sample could be obtained. These transects tended to be longer than those in the first period.

At each Clout’s Index sample site, we aimed to locate a minimum of ten A. verticillata trees that were at least five metres apart and had evidence of recent foraging. We recorded tree height and estimated the number of russet cones available in two categories (<500 and >500). We collected 10 russet cones from each sample tree, aiming to sample at least three different parts of the tree. Fewer than 10 cones were collected from six trees due to lack of availability.

The cones from each sample tree were placed in a labelled paper bag and stored on drying racks or in open baskets until dry (up to 3 months). Each year’s batch was fan dried in a bulk drying kiln for 44 hours at 60 degrees. Cones were warmed in a domestic oven prior to weighing, to assist in removing any moisture that may have accumulated since kiln drying and then allowed to equilibrate to room temperature for at least one hour. The cones and seeds were weighed separately to the nearest hundredth of a gram, using a digital balance. Clout’s index was obtained for each sample tree by dividing the seed weight by the seed-plus-cone weight, based on the method used by Clout (1989) and Crowley and Garnett (2001).

Notes