Managing a breeding population of endangered Carnaby’s Black Cockatoo Calyptorhynchus latirostris on the edge of their range
Data include vegetation community surveys (transects and quadrats) at nine sites, nest site characterisations of 21 confirmed nesting hollows and measurements from eleven nestlings.
Nest site characteristics
Nests were located following BirdLife Australia (2020) guidelines: observing hollow use by breeding and/or prospecting Carnaby’s pairs, identifying other signs of hollow use including chipping, feathers or feeding residue, using the ‘tap-and-flush’ method to determine if hollows were occupied and, finally, comprehensive searches of all potential hollows in suitable habitat using a lightweight camera (GoPro HERO7, San Mateo, California, USA) and click LED telescopic pen torch (Bunnings, Perth, Western Australia) attached to a 12m extendable fibreglass pole (Spiderbeam from TTS Systems, Stratford, Victoria) to look into hollows for the presence of breeding females (they don’t always flush), eggs or nestlings (Figure 2). Based on Carnaby’s requirements for nesting habitat (Saunders & Ingram 1987), nest searches were restricted to mature, hollow-bearing groves of open eucalypt woodland on or near the banks of the lower Murchison River. For each confirmed hollow (n = 21), we recorded GPS coordinates, tree species, tree diameter at breast height (DBH), tree and hollow entry height (m, using the Android app: Measure Height v1.4, Deskis OU), hollow entry type (chimney, spout, side, fork) and aspect (compass directions, vertical; BirdLife Australia, 2020). For a subset of hollows accessible by ladder (n = 12), we additionally recorded entry width (cm), hollow depth (cm) and width of the hollow floor (cm). Confirmed nesting trees were marked with numbered aluminium tags. Hollows showing no signs of use, or signs of use by other species, were noted but not measured or tagged.
Nestling measurements
Nestlings (n = 11) were weighed (g, using a Pesola 1000g spring balance scale, Schindellegi, Switzerland) and folded left wing measured (mm, using a stopped rule). Nestlings were aged by comparing the folded left wing measurement with a growth curve of the folded left wing measurements of nestlings of known age (Saunders & Ingram 1998, Saunders et al. 2020b). Nestling condition was assessed by comparing the measured nestling mass for a measured folded left wing length at MHS (n = 11, limited to nestlings with folded left wing length > 50mm) with the benchmark body mass for that wing length (Saunders et al. 2020b). Lay dates were estimated based on nestling age and an incubation period of 29 days (Saunders 1982) for 30 breeding attempts. The egg-laying period was determined based on estimated lay dates of the first and last clutches in each season.
Vegetation surveys
To assess the condition and quality of foraging and nesting resources available to the breeding population at MHS, we established eight permanent vegetation monitoring points, four in banskia woodland (S2-S5) and four in riverine eucalyptus woodland (S6-S9; Figure 3). At each point, we marked a permanent vegetation quadrat (20m x 20m) and 50m transect. We oriented the quadrats on the compass (corners at NEWS) and laid out transects in a northerly direction starting from the midpoint of the southern edge of each quadrat. Vegetation surveys followed Department of Biodiversity, Conservation and Attractions (DBCA) Standard Operating Procedures (SOPs) 6.1 (Clarke 2009a) and 6.2 ( Clarke 2009b). Vegetation surveys were conducted in September 2021, when both annual and perennial species were present and many species were in flower, aiding identification.
We recorded all plant species present within each quadrat. Herbarium specimens were collected and collated into a field herbarium book for identification on-site or in the herbarium. Vegetation structure, vegetation condition (healthy, not healthy, dead), soil type and landform within each quadrat were also noted. We used the point-intercept method (Jonasson 1983, 1998, De Stefano et al. 2021) along each transect, recording vegetation at 1m intervals. Variables measured at each point were ground cover (vegetation, rock, leaf litter, dead wood, bare ground), burn status and, if vegetation was detected, species, condition, canopy height (m, using a 5m tape measure or, if plants taller than 3m, the Android app: Measure Height v1.4, Deskis OU) and phenology (presence of flowers, fruit or new leaf growth). All observations were recorded in the field using CyberTracker software on a Samsung smartphone.
