Callocephalon fimbriatum (Gang-gang Cockatoo)

Nesting Research

Thanks for contributing to the Gang-gang nest hollow project.

Good data has been obtained from the Canberra area, where the majority of nests have been identified. Nests have also been identified in Campbelltown, Broulee, Berry, Moruya, Cooma, Tumbarumba, Bucketty, Olinda, Queanbeyan, Wombat State Forest (Vic) and East Melbourne.

We would like to compare what we have been finding at these sites with that elsewhere so we always welcome more records of Gang-gangs around hollows, particularly in remote or rural areas away from Canberra

Gang-gangs start to check out nest hollows around July but don’t start nesting until around October. Gang-gangs become very quiet and secretive around nests once breeding starts, so potential nest hollows are most likely to be sighted between July and October. Repeated observations at the same hollow are valuable records. Researchers can then check potential nests for actual breeding records from October onwards.

Highlights of research so far include:

• ·    The collection of data on hollow dimension, fledgling success rate, fledgling sex ratio (0.7 females to 1 male) and timing of fledging. A significant relationship was found between fledge time and altitude. Low altitude sites such as Campbelltown (50m) may have a breeding period 2 months in advance of that at high altitude locations like Cooma (1000m).
• ·    216 hollows that were of interest to Gang-gangs in the Canberra, Cooma and Tumbarumba areas were closely monitored. Of the 216 hollows it was found:
• 46% empty
• 9% Gang-gang nest hollows
• 10% empty but with chewed bark
• 12% occupied by Brushtail Possums
• 5% leaf-lined suggesting possum or perhaps Galah use
• 9% flooded (Gang-gang water source)
• 4% occupied by European Honey Bees
• 3% occupied by Australian Wood Ducks
• 3% occupied by Sulphur-crested Cockatoos
• 1% occupied by Galahs
• 1% occupied by Crimson Rosellas, Boobook Owls

These results possibly suggest that at least in the Canberra area hollows are not a limiting factor and that competition from other hollow nesting such as cockatoos and parrots is not a major factor. There is an on-going project in Canberra to help determine whether sites are limiting. Brushtail Possums are the major hollow competitor. The rate of predation is unknown but the project confirmed Brushtail Possums as a significant predator of eggs and chicks.

• At least some Gang-gang pairs will prepare multiple hollows before choosing one as a nest. Gang-gangs line their nests with bark chips of a distinctive shape and size. They appear to be choosing nest hollows on the basis of climate experience. In Canberra, in two hot, dry years, no hollow bearing dead trees were utilised while in the two most recent wet and cooler years, 6 hollow bearing dead trees were utilised. The clutches raised in the hot/dry and wet/cool years were similar (26 and 32 respectively).
• Only about a third of previously used nest hollows are used in any one year, but if a hollow is used one year there is a 50% chance of it being used the next.
• With the help of the ACT Government nest hollow dimensions have been measured and used to guide nest tube design. The nest tubes are currently being trialled as part of another project. With the Canberra nest hollows, the average height in a tree is 6.5m (range 2.5 - 10m). The average hollow entrance dimensions are height 22.4cm, width 15.2cm; largest breeding entrance measured is 39 x 24cm. The smallest breeding hollow entrance is 10 x 7cm. The average floor diameter is 20cm (range 12-33cm).
• It is problematic to attach trackers and bands to Gang-gangs so this has never happened. Consequently, little is known about their movement. One of our hollow observers (thanks Cath) alerted us to a male raising two chicks that had considerable crest damage and was easily recognisable. We put the call out for "Baldy" sightings and received sightings at 7 different locations. Four of these were during the breeding season. The furthest from the nest was 3.89km, where Baldy was foraging on Red Stringybark nuts, so this is the distance that we now know a Gang-gang raising chicks will at least travel to forage.
• Baldy also made repeated visits to a residence about 700m from the nest where he fed on Sunflower seeds. Caged Gang-gangs are known to suffer infertility and other health issues when largely fed on a sunflower seed diet. The impact of sunflowers in the diet of wild birds is unknown, but the project has highlighted it as a potential issue. 

Diet information

From Gang-gang Cockatoo diet as assessed by camera images and written records. Michael Mulvaney & Isobel Booksmythe, Australian Bird Study Association, Corella, 2023, 47: 8-15.

Thanks to the hundreds that contributed records to the Gang-gang diet study. While I have completed the analysis you still may like to keep adding feeding sightings, particularly where they are in more remote areas, as ongoing collation of records will better refine suitable species for use in Gang-gang habitat enhancement projects in your region.

In summary, 4,112 Gang-gang Cockatoo feeding records were collated from image-based records posted on social media and citizen science platforms and from written records of bird observer clubs and bird-based databases. The records covered the whole Gang-gang range but were clustered in and around the larger urban centres, particularly Canberra and Melbourne.

There were 275 food items recorded in the feeding records. Three taxa, Blue Gum Eucalyptus globulus, Hawthorn Crataegus sp. and Liquidamber Liquidambar styraciflua comprise a third of all the recorded 16,558 feeding events. A feeding event being the number of birds in an image or written record multiplied by the number of days over which feeding occurred in that record. The top twelve taxa account for 54% of all feeding events. Over half of the food items were recorded as being eaten only once or twice amongst the total record. Gang-gangs sample a wide range of foods, and have a varied diet, but the bulk of their feeding is targeted to a few taxa.

Of the plant species eaten 26% are exotic, which suggests Gang-gangs have adaptability to new food sources.

Gang-gangs eat from seven main food groups. These are, in terms of the proportions that they constitute to the recorded feeding events, eucalypt gum nuts and flowers (43%), berries with relatively large seeds but small fruits (21%), green cones of mainly the Pinaceae and Cupressaceae families (10%), wattles (7.5%), soft pods from a variety of tree and shrub species, but mainly Liquidamber (7%), nuts (mainly walnuts and oak) (3%), and invertebrates (mainly sawfly and lerp psyllids) (1%). Eating from the range of food groups seems to be of importance. Amongst the 10 most fed on taxa all of the first 6 of the above food groups are included.

Wattles are the main food item in November and December. Wattles remain a major food item in January but exotic berries become the main food item and continue to be so through February and March. Gum nuts and flowers increase their proportion in the diet from January onwards and peak as the major proportion of the total diet from May to August, and steadily decline for the rest of the year. Gum nuts and flowers remain the major food item during September and October.

Feeding records, during the September – January breeding season and within 4km of one of 57 known nest trees, were found to contain twice the proportion of gum nut/flower and cone feeding events as those recorded more than 4km away from a nest. They also included 3 times the rate of insect feeding.  Wattles remained an important part of the spring diet but comprise 22% of the proportion of feeding events close to nests while it was at 28% for records further away than this.

The Gang-gang diet differs across its range and this reflects both the food species that are available locally (both planted or indigenous to certain areas). However there also appears to be some cultural differences between populations with some widespread species such as Water Milfoil Myriophyllum sp., Dogwoods Cornus sp. or White Popular Populus alba only being eaten, or predominately so, in one bioregion. 

Collection bias limits comparisons being made between tall forests (where few records were obtained) and urban and peri-urban woodland and dry forest habitats (where the bulk of records were obtained). However, the data demonstrates that the latter habitats are important for foraging and breeding Gang-gangs. These habitats also support the vast majority of currently known nest trees.

The information obtained from the records you contributed is already guiding what species are best to use in restoration or enhancement of Gang-gang habitat or the choice of parks and garden plantings likely to attract Gang-gangs.

Thank you, Michael Mulvaney.