Are roads barriers for bird movements? The case of La Florida Provincial Reserve (Tucumán, Argentina)

Abstract

We studied the effect of a road on bird movements at La Florida Provincial Reserve (Tucumán, Argentina). A road cuts the reserve leaving a forest fragment detached from the continuous forest. Understory birds were captured monthly for 12 months using 12-15 mist nets located in forest sites on both sides of the road, and birds crossing the road were censused to estimate movement between the fragment (FG) and the continuous forest (CF). The captured birds were classified as site-attached (captured more than once) and transient individuals (one capture). If the road reduced the arrival of new individuals into the FG, the proportion of site-attached captures would be expected to be larger here than in the CF. We captured 1742 birds (34 species). Richness was similar for both sites (CF=27, FG=28). Site-attached abundance showed no differences between sites (CF=234, FG= 194), as well as the percentage of site-attached birds captured monthly. Transient individuals were significantly more abundant in continuous forest (809 vs. 505); Turdus rufiventris abundance was responsible for this difference. In censuses we observed 622 individuals (28 species). The high frequency of T. rufiventris individuals crossing the road (33.8% from total birds censused) suggests that this barrier should not affect their movements. Some species commonly captured in the nets were not detected crossing the road, suggesting that they may be affected by the road. However, none ol' these species showed differences between sites in the percentage of site-attached captured monthly. Finally, our results suggest that understory birds are not significantly affected by the discontinuity produced by the road. These results could not always be extrapolated to other forests, that would require particular studies.