Disclosing the determinants, drivers and predictors of bird depredation on date palm (Phoenix dactylifera L.) production

Bird intake and damage to fruits of Phoenix dactylifera is a common problem in date palm cultivation regions. Though plant vegetative characteristics and fruit nutritional values influence frugivory behavior in passerines, there is little knowledge about these parameters for sparrows feeding on dates, as most previous studies have focused on the impact of farm organization and location on the feeding choice made by sparrows. This study aimed to examine the effects of date palm tree traits and its fruit morphology and biochemical traits on the level of damage caused by hybrid sparrows to date fruits of three different date palm cultivars. In a traditional date palm plantation, three date varieties (Degla-Beida, Deglet-Nour and Ghars) were analyzed. The estimates of date production loss were correlated to several tree morphometrics and fruit morphological and biochemical traits, including the number of bunches/tree, bunch height, number of pedicels/bunch, number of dates per strand, total production/tree, and date fruit traits (length, width, weight, volume, pulp weight, ratio pulp weight/date weight, sugar content, water content and pH). We demonstrated that sparrows were attracted to bunches with low height and high fruit density, but they showed no interest to number of bunches per tree, number of pedicels per bunch, total number of dates and production per tree. Regarding date morphology, large and heavy dates were more likely to be selected by sparrows, although an unclear relationship was found between production loss per tree and date length, width and volume. In terms of fruit biochemical traits, sparrows damage rates increased with the increase in fruit pH, moisture, and total and reducing sugars. The average rate of lost dates per tree was 9.2 ± 7.66%, 8.4 ± 5.16%, and 3.9 ± 1.71% for Ghars, Deglet-Nour, and Degla-Beida, respectively. Significant differences were observed between cultivars in the amounts of damaged dates still on bunches or fallen on the ground. The hierarchical choice of dates by sparrows was also confirmed. Our results showed that soft dates were more preferred by sparrows than semi-soft and dry ones. The findings of this study indicated that it is necessary to provide extensive protection for highly attacked cultivars in palm groves.