Callocephalon fimbriatum (Gang-gang Cockatoo)

Update on  Gang-gang research

Nesting Research

Thanks for contributing to the Gang-gang nest hollow project. In total we have now identified 60 nests (52 in Canberra, 2 in Campbelltown, 2 in Wombat State forest (Vic) and one near or in Moruya, Cooma, Tumbarumba and East Melbourne). We continue to learn much about Gang-gang nesting ecology and behaviour. We have 5 years of good data from Canberra but would like to compare what we are finding here with that elsewhere. Gang-gang hollow checking is increasing as we approach breeding season and we ask that you keep posting sightings of where you observe Gangs-gangs looking into hollows, but particularly in remote or rural areas away from Canberra .

Highlights of last season’s research include

* A further 25 nest hollows have been identified across much of the Gang-gang's range. Hollow dimension data has been collected from most of the hollows as has fledging success rate, fledging sex ratio (0.7 females to 1male) 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 of hollows, in the Canberra, Cooma and Tumbarumba areas, that were of interest to Gang-gangs were closely monitored. Of these we found:

  
46% empty 
9% Gang-gang nest hollow 
10% empty but with chewed bark 
12% Brushtailed Possum 
5% leaf-lined suggesting possum or perhaps Galah use 
9% Flooded (Gang-gang water source) 
4% Bees 
3% Australian Wood Duck 
3% Sulphur-crested Cockatoo 
1% Galah 
1% Crimson Rosella, Boobook Owl

 
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 experienced. 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 24 cms The smallest breeding hollow entrance is 10 x 7 cms. 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

Thanks to the hundreds that contributed records to the Gang-gang diet study. I have completed an analysis and a draft report is being reviewed at the moment. When finalised I will provide a link so that anybody can download it. 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, 4112 Gang-gang Cockatoo Callocephalon fimbriatum 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 lerps (1%). Eating from the range of food groups seems to be of importance. Amongst the ten most fed on taxa all of the first six 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 three 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 albaonly 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 to 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