Gang-gang behaviours associated with nesting stages

Detailed information from Prof Michael Mulvaney

Gang-gangs peer into hollows all year round and will enter hollows to access pooled water. It appears that a Gang-gang pair will have multiple hollows of interest and that in the Canberra area they are most active around hollows they are examining as potential nest sites in mid to late September. Hollow selection appears to take some time and may relate to weather conditions and presence of predators, such as possums In the four years of study, three years have been hot and dry and all selected hollows found were in the main trunk or a primary branch of a live tree. Last year was wet and cool in comparison and for the first time we found nesting hollows in dead/near dead trees and in smaller spouts.

During this stage Gang-gangs are easy to see anytime during the day, are sometimes quite noisy and need to fight off other bird species and compete with possums for the hollows; these encounters can be very noisy. Some other birds, which seem to challenge for the hollows are sulphur-crested cockatoos, rainbow lorikeets and galahs.

Behaviours/signs to look out for
• Both partners of a pair entering a hollow (usually not at the same time).
• Multiple visits by a pair to the same hollow over multiple days (visits may be less than a minute).
• Chewing of bark around or near a hollow. (Gangs-gangs lay their eggs on about 2-3 cm of chewed bark. Gang-gangs do not line their nest with leaves.)
• Multiple pairs in the same vicinity (within a few hundred metres) – Gang-gangs tend to nest close to each other.
• Wood duck feathers around hollow entrance. Wood ducks are early season nesters. Gang-gangs and wood ducks can use the same hollow in the same year.
• Gang-gang pair driving other birds away from a hollow.
• If Gang-gangs are calling loudly or “growling” down a hollow, with raised wings, it means that the hollow is probably occupied by a threatening animal such as a brushtail possum or boobook owl.

INCUBATION (October–early November)
The female spends the night on eggs, while during the day the male and female share incubation responsibilities. Thus there is always one bird in the nest. Incubation takes about 4 weeks. There is very little activity at all around the hollow and this may involve as little as two nesting sitting change-overs in a day. Change-overs can be quick and easily missed. The non-nesting bird spends very little time around the nest site. In Canberra most incubation begins mid-October but it can occur well into November. At least one pair has also switched hollows early in the season and begun again at a new site. This may have been in response to possum visitation.

Behaviours/signs to look out for
• Male or female seen sitting inside and on the edge of the hollow, looking out.
• Change-over. The incoming Gang-gang gives a very small call on the way in which gives the one on the egg(s) time to be prepared. It then comes in and changeover occurs. During this period the Gang-gangs are very quite, changeover happens in a matter of minutes. Best time to observe an incubation changeover is within the hour after dawn when the female leaves or in the evening when the females takes on night duties. Change-overs can occur at any time of the day.
• There is little Gang-gang activity around hollow.

The female continues to spend the night on the nest. Both partners feed chicks during the day, but initially only a few feeding visits are made each day. Young leave the nest about eight weeks after hatching.

Behaviours/signs to look out for
• Female leaving or entering hollow at times other than early morning or late evening.
• The Gang-gangs appear to be happy to be away from eggs/young chicks for longer periods at changeover and the frequency of changeover increases, to at least a few times a day.
• Chicks chirping from inside hollow can sometimes be heard and you may also hear them being fed.
• Both partners visiting hollow during the day and may leave hollow together. Other Gang-gang couples may accompany a returning adult and be present during change-over. These birds may help “guard” the hollow when both adults are away. A Gang-gang pair or individual looking into a hollow may not be the parent but they will not be seen entering the hollow.
• Adult birds driving other birds away from hollow. Note adult birds from other nearby nests will drive other species like lorikeets and sulphur-crested cockatoos away from a neighbour's nest.
• Birds calling to and joining other nearby nesting Gang-gangs on foraging flights
• As the chicks grow, both parents are required for feeding with frequent feeding happening every hour or two.

The average depth of a Gang-gang hollow in Canberra is about 50cm. When birds are getting near fledgling, parents encourage the chicks to climb to the hollow entrance by feeding them there. Chicks will stay perched at the hollow entrance and are visible over a 3-11 day period, just prior to fledging. The average is 7 days per chick. Longer visibility times usually involve multiple chicks. Thus the window in which a nest hollow can be confirmed purely by observation is short. In Canberra most chicks are first observed between Christmas and 15 January but has occurred from 8 December to 26 February. Time from laying to fledging varies from 61 to 79 days.

Behaviours/signs to look out for
• Chicks chirping from inside hollow can sometimes be heard.
• Parents perched on hollow with head in hollow, body or at least head rocking rapidly.
• Heads of chicks appearing above hollow entrance. Gang-gangs usually have between 1-3 chicks per nest with two being the most common. Chicks can develop at different rates so not all may be visible at one time. Thus determining the number and gender of chicks at a nest hollow should include multiple visits – preferably two a day once chicks are visible.
• In Canberra during the days of record temperatures and smoky air of the 2019/2020 season, we had chicks leaving the nest prematurely and falling helplessly to the ground. Where these chicks (two occasions) were replaced back into a hollow (by a volunteer climber) they were cared for by parents and successfully fledged. On the one occasion where a chick couldn’t be replaced it was predated.
• If a chick falls to the ground the adults will continue to feed it so do not disturb unless there is the possibility of predation. If a climber is available then placing it back in the hollow is best.
• Both Gang-gangs are present at fledging, seemingly encouraging the young to leave the hollow through calling, being close by, making repeated short flights from the hollow and if the young followed rewarding them with food. This process can take a number of days.
• The fledged chick will fly to a nearby tree, where both parents will then preen and feed the chick.
• Chicks do not return to a hollow once fledged.
• The newly fledged chicks in the area tend to form creches for a while and a large number of chicks can be seen together at times.

由使用者 barv barv2021年09月24日 07:39 所貼文




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