The effect of traffic noise on the breeding density of 20 passerine species was examined over a 2-year period in three different road types passing through pasture-woodlands in western-central Spain. No statistically significant differences were observed during the 2 years studied. An average of 19.6 birds/10 ha was recorded for the low-traffic road (LT), 21.7 birds/10 ha for the medium-traffic road (MT) and 19.1 birds/10 ha for the high-traffic road (HT). A total of 11 species (55%) did not show any statistically significant differences in breeding density among the different types of roads. By contrast, other species, such as the Blackbird, the Iberian Shrike and the Linnet, did point to differences between the MT and HT roads. House and Rock Sparrows, as well as the Corn Bunting, showed higher breeding densities near the HT road. The opposite effect was observed for the Wheatear, the Iberian chiffchaff and the Woodlark, for which high breeding densities were recorded in the vicinity of the LT road. Our results suggest that traffic noise constitutes a serious problem for at least 15% of the breeding bird community. Palabras clave: Noise, Population