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).