A particle-hole model is developed to describe the excitation spectrum of single Λ hypernuclei and the possible presence of collective effects is explored by making a comparison with the mean-field calculations. Results for the spectra of 12 Λ C, 16 Λ O, 40 Λ Ca, 90 Λ Zr and 208 Λ Pb hypernuclei are shown. The comparison with the available experimental data is satisfactory. We find that collective phenomena are much less important in hypernuclei than in ordinary nuclei.