Background and Data collection (Aim 2)
For the second aim of the study (evaluate the fitness consequences of
the captive wing phenotype) I used orange-bellied parrots (Department of
Environment Land Water and Planning 2016) as a model because they: (i)
are bred in captivity and released in large numbers (Smales et
al. 2000) which overcomes the common hindrance of small sample sizes,
(ii) undertake a migration that results in strong selection and survival
of only a fraction of individuals (Stojanovic et al. 2020b),
(iii) their recovery program is among the largest, longest running and
most well-resourced of threatened species’ recovery efforts (Department
of Environment Land Water and Planning 2016; Pritchard et al.2022) making it a ‘best case’ of captive-breeding for conservation, and
(iv) I have previously demonstrated that the wings of captive and wild
parrots have different shapes (Stojanovic et al. 2021), so
identifying fitness consequences of this difference a priority.
Captive-bred juveniles are released at the end of the breeding season so
that they can integrate with wild fledglings and migrate northward
together. This migration is demanding both physically (e.g. a sea
crossing) and behaviorally (e.g. sudden transition from supplemental to
natural food (Stojanovic et al. 2020a)). Most captive-born
juveniles do not survive their first year of life (Stojanovic et
al. 2020b). Their survival is monitored via daily observations of
ringed birds at supplementary food tables during the summer breeding
season (Stojanovic et al. 2018; Stojanovic et al. 2020b).
The captive population is held across several participating institutions
that use comparable husbandry approaches (Pritchard et al. In
Prep) and a studbook to minimize genetic adaptation to captivity
(Morrison et al. 2020a). Regular releases have resulted in full
admixture of the captive and wild populations (Stojanovic et al.2022).
I measured 78 juvenile captive-bred parrots released to the wild over
three years (2019: 30, 2020: 31, and 2021: 17). Juveniles are selected
for release based on metapopulation management considerations (Morrisonet al. 2020b; Troy & Lawrence 2021), but not for any particular
phenotypic trait other than good body mass and general feather
condition. To reduce the welfare impact of measuring live birds, I only
measured ΔQ for P10-P5 because these are the most likely feathers to
vary in their length (Stojanovic et al. 2021). I also dropped
LS to further reduce handling time, but I did record
LW, tail length (LT) and body mass (g).
P9 was excluded from analysis as it was the longest feather in the wing
of each parrot (and thus there was no variation to model). As an index
of individual condition, I divided body mass by LW to
scale for body size. I scored individuals as having survived (1) or died
(0) their first year of life based on whether or not they returned from
their first migration (Troy & Lawrence 2021).