This note examines the effects of habitat, landscape, climate and geographical situation on the occurrence probability of the Red-backed Shrike at its westernmost range boundary. The results from 127 sampling localities distributed east-to-west along 600 km in northern Spain reflect local and regional effects on species distribution. Habitat patch size (the species prefers large patches) and summer temperatures (the species avoids warmer sites) are the two main environmental correlates of species distribution. In addition, the occurrence of the Red-backed Shrike decreased in the westernmost sectors of the study area. This result could be related to a peninsula effect potentially reinforced by the atypical migratory circuit of this summer passerine (birds arrive from the east). The conservation prospects of this peripheral population suggest a retreat to cold highlands as global warming increases, a reduction in suitable habitat patches due to forest encroachment resulting from rural abandonment and the reduced availability of individuals to offset local extinctions in the westernmost border of its European range. —Tellería, J.L. (2018). Distribution of the Red-backed Shrike Lanius collurio at its western range boundary: patterns and conservation prospects. Ardeola, 65: 221–232.