Study area and species
The study was conducted in northeast Portugal, along the Douro river
valley and surrounding areas, which corresponds to the last stronghold
of the black wheatear in the country. This population occurs mainly in
traditional vineyards and olive groves (terraces with stone walls) and
is spatially isolated from the remaining Iberian population.
The black wheatear is a highly territorial passerine that occurs in arid
and semiarid regions of the Iberian Peninsula and North Africa. Although
the species is not globally threatened, European populations are
declining, and the species is now considered regionally Vulnerable in
Europe (BirdLife International, 2015) and Critically Endangered in
Portugal (Cabral et al., 2005). Previous studies using conventional
morphological approaches have shown that the species feeds on a wide
range of animal and plant food items, no study has shown any sexual
dietary differences.