Summary of last season's Gang-gang tree hollow research findings

An update from Gang-Gang project
Thanks to the many of you that contributed 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 were 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.
Michael Mulvaney

由使用者 barv barv2022年07月23日 23:36 所貼文




登入註冊 添加評論