Reproductive success and demography of the Orange-bellied Parrot Neophema chrysogaster
Holdsworth, MC (2006) Reproductive success and demography of the Orange-bellied Parrot Neophema chrysogaster. Research Master thesis, University of Tasmania.
The Orange-bellied Parrot is one of only two obligate migratory parrots in the world.
The species is listed nationally as endangered and has been the subject of intensive
study and conservation activities over the past 25 years. Reproductive and
demographic data collected over this period from the wild population form the basis
of this thesis.
Remote breeding sites in southwestern Tasmania at Melaleuca and Birchs Inlet were
used to study this species in the wild. Through deployment of up to 52 artificial nest
boxes and observations of natural nests at Melaleuca it was possible to collect
information on a range of reproductive success parameters over a long period,
including 12 consecutive breeding seasons. In addition, the provision of up to 33 nest
boxes over seven consecutive years at Birchs Inlet provided a comparison with the
use of nest boxes by several competitors at Melaleuca. The use of colour-bands to
identify 760 individuals from 16 different cohorts provided the means to assess a
range of behavioural and demographic parameters of the species.
This study confirmed the Orange-bellied Parrot has a regular migratory pattern with
birds beginning to return to the breeding area on the 2nd October (plus or minus 5.1 days s.d) in
each year. The first birds to return are those in their second year of life or older, while
first-year adult birds begin to arrive 13 days later. The median arrival date for birds in
their second year or older was the 23rd October compared with 9th November for firstyear
adult birds. There was no difference between the sexes in arrival date. The mean
date of last departure from Melaleuca was 5th April (plus or minus 11.1 days s.d).
A total of 190 nests with known contents were studied in the wild and, of these 185
nests contained eggs and five nests contained no eggs. This study found the earliest
laying date was on the 29th November and the latest was the 19th January with eggs
(95%) laid during December (n = 101 eggs). Clutch size ranged from 2-6 eggs with over half of the clutches having 5 eggs and 95.3% of all clutches 4-6 eggs in size. The
mean clutch size was 4.7 eggs per active nest across all years and there was no
evidence the species can produce second clutches in the wild. The mean incubation
period for Orange-bellied Parrot eggs was 21.4 plus or minus 0.8 days (n = 49 observed
incubations). The mean dimensions of unhatched eggs was 22.9 plus or minus 0.98 mm by 18.5 plus or minus 0.67 mm (n = 99 eggs).
The 185 nests with eggs studied by this work contained a total of 874 eggs. Of these
695 eggs hatched and 179 eggs failed to hatch. Of the 179 failures, 107 eggs (69.7%)
were infertile, 48 eggs (26.8%) were fertile and 24 eggs (13.4%) were of unknown
fertility. Of the 48 unhatched fertile eggs, 23 eggs (47.9%) were early-term failures, 15
eggs (31.2%) were mid-term failures and 10 eggs (20.8%) were late-term failures. The
mean egg fertility rate for the species was calculated to be 85.6% (plus or minus 2.91 s.e).
Hatching success from all eggs laid was 79.5% (i.e. 695 nestlings hatched from 874
eggs laid) with the mean hatching success across all years being 80.2%. A total of 89
nestlings died prior to fledging. Early stage deaths represented 44.9% (n = 40) of all
mortalities and late stage deaths 55.1% (n = 49). The annual egg failure and nestling
mortality varied across years. Of a total of 268 egg and nestling failures across all
years, 66.8% (n = 179 eggs) were attributable to hatch failure and 33.2% (n = 89
nestlings) to mortality. Unhatched infertile eggs represented most (39.9%, n = 107) of
all failures. Of the 190 nesting attempts, only 27 failed to produce any young. The
most common cause of total nest failure was attributed to failure to hatch (44.4%, n =
12) followed by nestling deaths (37%, n = 10) and no eggs laid (18.5%, n = 5).
Average brood size was 4.0 nestlings plus or minus 0.09 s.e (range = 1-6) from 173 nests with
65.9% of nests producing four (33.5%) or five (32.4%) nestlings. The majority of nests
produced four fledglings with a mean fledgling brood size of 3.7 plus or minus 0.09 s.e (range = 1-6) from the 163 successful nests. Only 4.3% of successful nests produced the
maximum of six fledglings.
Of the 190 Orange-bellied Parrot nests studied, 85.8% (n = 163) produced fledglings.
The distribution of nest productivity is presented and discussed in detail. The number
of fledglings produced per breeding attempt varied between zero and six. A total of
69% of all nests produced 3-5 fledglings whereas 33% of all nests produced four
fledglings. The fledging success for 12 consecutive breeding seasons was 87.2% (606
fledglings from 695 nestlings) and the mean fledging success across all years was
86.9% (plus or minus 2.47 s.e). The overall breeding success for the Orange-bellied Parrot was
69.3% (606 fledglings from 874 eggs laid). The overall reproductive output of the
species was 3.3 fledglings per nest (606 fledglings from 185 nests) from an investment
of 4.7 eggs laid.
Egg fertility, nestling survival and fledgling survival of Orange-bellied Parrots in the
wild is noticeably higher than for the captive population, and is equal to or exceeds
many other Psittacidae. The reproductive success results reported here are
comparable with the more common Turquoise Parrot Neophema pulchella of mainland
Australia. Although the Orange-bellied Parrot has a healthy mean fecundity rate of
1.62 females/egg laying female, there was some variability between years, with a low
of 0.87 females/egg laying female in 1998/99.
The mean lifespan of the Orange-bellied Parrot was calculated to be 2.22 years (plus or minus 0.074 s.e, range = 0.37-11.70, N = 693) with no significant difference between male and
females. Males lived on average for 2.75 years (plus or minus 0.127 s.e, range = 0.43-11.70, n = 240)
and females lived on average for 2.67 years (plus or minus 0.141 s.e, range = 0.18-10.41, n = 189).
The oldest male recorded was 11.70 years of age and the oldest female recorded was
10.41 years of age. This study was not able to compare the reproductive lifespan of
wild Orange-bellied Parrots with captive-bred birds due to database problems or with other Psittacidae due to lack of comparable studies. The capacity to compare the wild
population with captive-bred birds and other Psittacidae will greatly enhance our
knowledge of the species.
This work suggests the Orange-bellied Parrot does not have a strong fidelity to mates,
nest site or nesting zone. This finding is contrary to previous assumptions made about
the species. This study did not measure hollow availability; however, a comparison of
the use of nest boxes between Birchs Inlet and Melaleuca indicates competition from
introduced species may be limiting the breeding range and reproductive success.
Survivorship rates of juveniles to first breeding (c. one year old), adults and both
sexes were determined. Mean survivorship of juveniles over the study was 55% (plus or minus 3.2
s.e) and is within expected limits when compared to other Psittacidae. Mean
survivorship of adults was 63.6% (plus or minus 2.0 s.e). There was a decreasing trend in survival
rates across all cohorts from 1999 onward with average annual survival declining
markedly thereafter. The reason for this decline is unclear. There was no difference in
survival rate of each sex over the study.
This study has significantly increased our understanding of the reproductive success
and demography of the Orange-bellied Parrot. This information will reduce the level
of uncertainty in the Population Viability Analysis model for the species and, in turn,
increase the power of such models to assess the species status and test the
effectiveness of conservation measures. Some of the results of this study have
important implications for future research and conservation of the species. These are
discussed, and include management of nest boxes, refinement of mark-recapture
studies, population viability analysis and influence of introduced nest competitors.
|Item Type:||Thesis (Research Master)|
|Keywords:||fauna, tasmania, parrot, orange-bellied parrot, endangered species, birds|
|Deposited By:||utas eprints|
|Deposited On:||18 May 2007|
|Last Modified:||18 Jul 2008 19:54|
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