Morphometric traits of gizzard in relation to feeding habits of wild Sardinian partridges (Alectoris barbara barbara, Bonnaterre, 1790) with particular regard to clast selection

Housing and feeding practices of wild birds for conservation management of biodiversity or restocking play a crucial role in determining the survival rates of animals when released into nature. Failure in coping with the environment might be one of the main flaws captive animals can experience when put into natural habitat. The present investigation aimed at exploring feeding habits and related morphometric traits of gizzard with respective content from wild partridges in comparison with captive ones. A total of 52 hunted wild Sardinian adult partridges (Alectoris barbara barbara Bonnaterre, 1790) were used. By comparison, 42 captive adult partridges reared in cages were enrolled. From each animal, the morphology of gizzard was investigated and respective content analysed for gross composition and taxonomical determination of fractions. Wet sieving analysis of each gizzard content was carried out (four‐sieve towers with different mesh sizes: 1 mm, 500 μm, 250 μm and 125 μm), and relative and absolute weight of fresh filled and empty gizzards were recorded. Thickness of muscular layer of gizzard wall was measured by stereomicroscope. Carcass weight significantly (p < 0.05) differed between captive vs. wild partridges (478 ± 21 and 305 ± 35 g respectively). Post‐mortem inspection highlighted gross morphological differences of gizzards between the two groups. Fresh weight of empty gizzards was 6.37 ± 0.80 vs. 11.25 ± 1.82 g, with average pH values of digesta 4.97 ± 0.11 vs. 4.38 ± 0.28 in captive vs. wild partridges respectively. Gizzard content from wild partridges accounted a 61.7% vs. 38.3% of biological vs. non‐biological material proportions (DM basis). The non‐biological material was mostly represented by lithic fragments and minerals (quartz, feldspar, calcite and mica) with specific peculiarities in terms of granulometry and morphometry. Feeding the captive partridges should point to support morphological and functional adaptation of gizzards to the feeding stuffs naturally available in the environment.