Hollow occupancy suggests Brushtail Possums may be a greater concern than nesting bird competitors

Over the last three years citizens have made over 500 image based reports of Gang-gang activity at tree hollows. Thank you, to all those who reported sightings. Trees with multiple records or where Gang-gangs were observed entering or leaving hollows were prioritised for checking. The occupancy of hollows during this Gang-gang breeding season was initially checked by visible observation and if no activity was observed then with a pole camera. To date, one Hundred and ninety hollows of known Gang-gang interest were checked in the Canberra area, fifteen at Cooma and four at Tumbarumba.

The following are the initial results

1 Hollows empty – 109 (52%)

  1. Gang-gang nest hollow – 22 (11%) note two nests seem to be no longer active
  2. Flooded (hollow a likely water source) - 19 (9%)
  3. Brushtail Possum in hollow - 18 (9%)
  4. Hollow lined with many gum-leaves suggesting possum use - 12 (6%)
  5. Now a bee-hive -6 (3%)
  6. Galah nest hollow – 6(3%)
  7. Wood-duck eggs or eggshell in hollow 5 (2%) – woodducks have an earlier breeding season and sometimes woodducks and Gang-gangs can use the same hollow within a year
  8. Sulphur-crested Cockatoo nest hollow 4 (2%)
  9. Crimson Rosella nest hollow 1
  10. Rainbow Lorikeet nest hollow 1
  11. Kookaburra nest hollow 1
  12. Boobook Owl roost/nest hollow 1

At least eight of the empty hollows were known Gang-gang nest hollows in previous years. At least three previous nest hollows were flooded this season. Over half of the hollows in which Gang-gangs were observed entering, leaving, chewing bark around or looking into, were empty. Galahs, Sulphur Crested Cockatoos, Rainbow lorikeets and Corellas have all been suspected as being significant competitors of Gang-gangs for nesting hollows, but between them they only occupied 5% of the inspected hollows.

Brushtail possums were observed in 9% of the hollows, with evidence of possum use found in a further 6% of hollows. No Gang-gang nests were found in trees in which Brush-tail Possums were observed but on a few occasions Gangs-gangs were found nesting in the same tree as Sulphur Crested Cockatoos.

Once completed and nest images checked the results will be subject to further analysis, but your work is already providing valuable insights. It is hoped that the Canberra results (were the Gang-gang population is steady) will be compared to that of areas where they have suffered significant and drastic declines – so please keep those tree hollow activity records flowing in.

Posted by michaelmulvaney michaelmulvaney, December 20, 2021 07:55 PM

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