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

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The Sardinian partridge (Alectoris barbara barbara, Bonnaterre 1790) is an avian species of the Family of Phasianidae, Order of Galliformes, which spreads widely through the Isle of Sardinia, Spain and north‐western Africa (Algeria, Morocco and Tunisia). Rearing of Sardinian partridge for conservation management of local biodiversity or as game birds for restocking is allowed in authorized private and regional farms. The presence of wild Sardinian partridges in the wild is limited. For this reason, the conservation status for this avian species is categorized as ‘Endangered’ (Tucker and Health, 1994). The number of games shot in 1 day per hunter is strictly ruled during the hunting season, yearly. At the moment, captive partridges can be released in the nature for recreational activities only, in authorized reserves of the Sardinian Autonomous Region. Housing conditions of Sardinian partridges were extensively improved over years (Cappai et al., 1975; Cossu et al., 1993) leading to successful reproductive performance of this wild bird in captivity. However, the release of adult specimens into the wild often leads to low survival rates and this represents a critical issue, above all in the case when re‐establishment of extinct or endangered species should be planned (Santilli et al., 2012). At this regard, housing and feeding practices of game birds may play a crucial role in determining the survival rates of animals when released into natural habitat. Failure in coping with the environment might be one of the main flaws captive animals can experience once released. Thus, the period before the release of captive partridges seems to represent a strategic moment to allow the adaptation of adult specimens to the natural habitat, also through adequate feeding practices. The literature lacks information about housing and feeding of partridges before their release into the wild, and the data available are based on few studies (Moniello et al., 2003, 2005; Fadda et al., 2008). Only recently, a housing model to improve the natural behaviour of reintroduced red‐legged partridges against predators has been proposed (Santilli et al., 2012). In comparison with captive mammals, one peculiar aspect in the physiology of avian nutrition is represented by the lack of teeth. The reduction of feed into small‐sized particles is a mechanical process actively involved in the performance of digestive physiology, particularly after the reintroduction into the natural habitat. Birds operate this physiological function in the gizzard. Thus, not only feed selection belongs to survival priorities, but conditions predisposing to the optimal utilization of natural feeding sources appear to play a key role. Given the extreme difference in terms of physical forms between natural feeding stuffs and manufactured feeds commonly used in the feeding practices of captive laying partridges, the availability of adequate feeding sources should be guaranteed to birds, prior to their release into nature.
The present investigation aimed at adding new insights on feeding habits of wild Sardinian partridges and filling the gap about morphological and functional traits of gizzards in relation to the natural diet, as outcomes of selection of natural feeding sources. In particular, clast selection by the wild bird was explored and effects on gizzard morphology were evaluated in comparison with morphometric traits from captive ones.
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