It’s now just over five weeks since the Mainland Release Trial partners released the first Orange-bellied Parrots (OBPs) at two sites in coastal Victoria. Since the last update two weeks ago, we have been monitoring birds regularly and collecting data on their movement patterns, habitat use, foraging behaviours and social groupings. We have also been on the lookout for any wild OBPs arriving from Tasmania.
The Spit (Point Wilson) release
Thirteen birds were released at the northern end of The Spit Nature Conservation Reserve this year, a group made up of five assisted-migration birds and eight birds bred at Healesville Sanctuary. Of these, a captive-release bird was unfortunately found predated (killed) in the week after release.
Of this release group, seven birds have been regularly seen in the last two weeks exploring the area around the Spit and Lake Borrie. The 9 km of coastline between these two sites offers a wide variety of native food plants and we’ve recently seen the group feeding on Austral Seablite and Beaded Glasswort - both traditional OBP autumn/winter food plants.
Some of these individuals are now mixing with four of the birds from the 2019 Mainland Release, including a female who was released at the 2019 Western Treatment Plant release site and was last seen in September at Werribee Open Range Zoo. These birds have good local knowledge of the area, which we hope will benefit their more recently-released companions.
Excitingly, we have also observed the arrival of three natural migrants, who have been interacting with this group at different times in the last two weeks. These natural migrants have found their own way to the area from the breeding site in Tasmania and include:
• adult female Silver Silver C (returning for her second winter at the site; the 2019 release birds would be known to her)
• juvenile female Blue D Yellow, who has arrived for her first winter. This female was captive-bred in Tasmania and released at the breeding site in southwest Tasmania in February
• juvenile male Purple Green B, who has also arrived for his first winter. He is a wild-born bird.
[Edit: another wild, natural migrant has joined the group. See separate post for details.]
Unfortunately, five individuals from the release group have not been seen in the previous two weeks. Only two of these were released with radio-transmitters. Given the birds we have located have been spending a lot of time in dense parts of the saltmarsh not accessible on foot, we hope some of the missing birds may in fact be with them, and simply evading detection. Of the two satellite tag birds, one has not been seen since three days after release (though a weak signal was received recently) and the other was seen in the last two weeks, still wearing its tag, though signals from the tag have not been detected in this period. We will be using a new receiver to search for these tags on the ground.
The north Western Port Bay release
The second group was released at north Western Port Bay and consisted of 13 captive-bred birds from Moonlit Sanctuary. As mentioned in the previous update, the flock of OBPs at this release site received recall training whilst in the aviary, leading up to their release. The aim of this conservation training was to: instill site fidelity in the birds so that they would remain in the area post-release, and to encourage the birds to return to the aviary post-release upon them hearing an auditory cue (produced by a whistle), to enable monitoring of their presence and visual health. The training produced strong recall behaviour in the birds while they were in the aviary leading up to the release day.
The recall training was performed three times per day up until 10 days prior to release, at which point we then introduced local wild food: this saw a lag in the birds’ response time to the recall. Following this we amended our training plan for the remainder of the birds’ time in the release aviary, to adapt to their new response, which once again resulted in the desired recall response returning. On the afternoon of the day of their release, the recall training was carried out as per usual, however, the birds did not respond by returning to the aviary. The delivery of the auditory cue was continued for a further seven days post-release, with no change in the birds’ response, and they chose to remain wherever they were (for some birds this was foraging out in the saltmarsh adjacent to the release site).
Six birds from the release group have been seen in the last fortnight consisting of two handraised birds (both wearing transmitters), and four parent-raised birds (three wearing transmitters). Of the remaining six birds that have not been seen or detected in the last fortnight (remembering that one of the original 13 birds was recaptured due to an attack by a Grey Butcherbird), two are hand-raised birds and four are parent-raised birds; and this includes three birds not wearing transmitters making them difficult to search for, two wearing radio transmitters and one wearing a satellite tag. Signals from the satellite tag have not been detected in the last two weeks. We will be using a new receiver to search for these tags on the ground.
One parent-raised bird has been visiting the OBPs in the breeding facility at Moonlit Sanctuary, while also being detected out in the saltmarsh in Western Port Bay, presumably where she is foraging. The other five have been seen regularly in saltmarsh habitat as a single group, or two separate groups of two and three birds.
The birds at this site are still primarily eating Beaded Glasswort but have been occupying a greater number of sites within the saltmarsh, which appears to be coinciding with fine-scale changes to the lushness of the Beaded Glasswort (senescing in some areas while remaining green and lush in others).
Blue-winged Parrots (Neophema chrysostoma) have been observed in the area, often with the OBPs, and on one evening the two species were observed flying to a roost site together in the mangroves.
At both sites, survey efforts are expanding to look for the missing individuals as well as more wild birds and collect information on the behaviours, food and habitat selection of the wild and released birds. We are also trialling the use of drones to perform radio tracking, which may greatly increase search efficiency and improve our chances of detecting missing birds.
The Mainland Release is a partnership between Victoria's Department of Environment, Land, Water & Parks (DELWP), Zoos Victoria and Moonlit Sanctuary Wildlife Conservation Park, assisted by BirdLife Australia, Melbourne Water, Parks Victoria and the Tasmanian OBP Program.
This year we are undertaking our monitoring with modified procedures to keep an eye on the birds while also observing social distancing to keep our community safe.
We encourage all sightings of OBPs in the release areas to be reported to OBP.Release@delwp.vic.gov.au.
First photo: birds from The Spit release site feeding in Austral Seablite, by Paul Rushworth
Second photo: two of the juveniles that are being regularly seen, wearing transmitters and foraging on Beaded Glasswort in Western Port Bay, by A. Herrod
No comments:
Post a Comment