usneoides) occurred on some of the large trees, although they were not as dense as in other forests at SANWR.
Both the bird and plant communities have changed markedly between the 1970s and the 1990s in a study site at SANWR. The bird community is now more typical of Tamaulipan thorn-forest, due to the loss of some forest bird species such as Altamira Oriole and the arrival of several new bird species typical of thorn-forest and thorn-scrub, such as Long-billed Thrasher, Northern Cardinal and White-eyed Vireo (Rappole & Blacklock 1994; Parker et al.
Total bird density now approaches that reported by Davis (1940) who studied birds in a riparian forest at SANWR which had a dense understory and shrub layer.
The disappearance of the Altamira Oriole from the study site is harder to explain, since they forage frequently in scrubby or successional areas and 3-4 pairs nested at SANWR during 1994-1996 (Brush 1998a).
Death of large trees has been noted in several areas at both SANWR and Bentsen-Rio Grande Valley State Park, particularly during severe droughts (Brush 1998a).