  The short-range organization around Ni atoms in orthorhombic $R$NiO$_{3}$
($R$=Pr,Nd,Eu) perovskites has been studied over a wide temperature range by Ni
K-edge x-ray absorption spectroscopy. Our results demonstrate that two
different Ni sites, with different average Ni-O bond lengths, coexist in those
orthorhombic compounds and that important modifications in the Ni nearest
neighbors environment take place across the metal-insulator transition. We
report evidences for the existence of short-range charge-order in the
insulating state, as found in the monoclinic compounds. Moreover, our results
suggest that the two different Ni sites coexists even in the metallic state.
The coexistence of two different Ni sites, independently on the $R$ ion,
provides a common ground to describe these compounds and shed new light in the
understanding of the phonon-assisted conduction mechanism and unusual
antiferromagnetism present in all $R$NiO$_{3}$ compounds.
