Demography and habitat requirements of Barbary partridge in Northern Sardinia

The Barbary partridge is widespread across North Africa, where it occurs from the coastal plains to the Atlas Mountains and edges of the Sahara. In Europe the species is present on Gibraltar, where has spread to adjacent Spanish mainland, in Canary Islands and in Sardinia Island. In Sardinia the species is widespread but since 2000s it has declined throughout the entire island mostly due to over-hunting, habitat degradation, in particular the removal of Mediterranean bush to improve livestock and agriculture. At present both biology and ecology of Barbary partridge is still poorly known, therefore the aims of our study were to assess demographic parameters, to model habitat suitability, and to individuate which habitat variables could affect population persistence. We studied the partridges in 34 study areas located within the Province of Olbia-Tempio (North Sardinia) from September 2011 to August 2012. We monitored partridges by pre and post-breeding censuses : winter coveys in November-December 2011 by the mapping method, pairs in April-May 2012 by the calling-count method from random points, and broods in July-August 2012 by the mapping method with hunting dogs. A tape-recorded call was used in spring to increase pair detectability. We mapped the location of each observation on 1:10,000 aerial photographs and recorded the number of detected birds, the distance of calling pairs, the number and the age class of chicks. We estimated the following main demographic parameters: average covey size, pair density by the Distance sampling, brood production rate (BPR), brood density, average brood size and chick survival rate. All parameters were estimated in each study area with the exception of average brood size and chick survival rate. Habitat suitability for partridges was investigated by the Maximum Entropy modeling (MaxEnt) performed on pair and brood observations, using Regional land use map and Digital Elevation Model. Pair and brood density averaged 22.9 pairs/km2 (S.E.= 3.96) and 2.5 broods/km2 (SE = 0.68). Mean BPR and brood size were 20.9% (SE = 11.1) and 6.7 (± 0.63), respectively, while chick mortality was 9.1%. The Maxent model showed that suitable areas for Barbary partridges should be characterized by low percentages of fallow fields, urban areas, rocks without vegetation and water with bushes, and by great percentages of Mediterranean scrubland and pastures. The North exposure reduced habitat suitability for the species. The Province of Olbia-Tempio was mostly unsuitable for partridges (67%), while the low-medium and high suitable classes accounted for 23.5% and 9.5% of the whole territory. Population dynamics of partridges inhabiting the northern province of Sardinia seemed characterized by low production rate which could lead to low brood production and juvenile recruitment. The low habitat suitability for breeding partridges, poaching and unsuited managed actions could cause the low population productivity by reducing suitable habitats for nesting, disturbing and killing breeding adults, increasing nest predation and clutch mortality during the first two weeks.