Breeding abundance and nest-site distribution of the Altamira oriole at Santa Ana National Wildlife Refuge, Texas

摘要

The distribution of the Altamira oriole (Icterus gularis) in the United States is restricted to the Lower Rio Grande Valley of southernmost Texas. Our objective was to assess the current breeding status of this species at and near Santa Ana National Wildlife Refuge (SANWR), a principal nesting area in the region. During each breeding season from 1997 to 1999, we attempted to find and monitor all Altamira oriole nests in and within 0.5 km of SANWR to determine annual breeding-pair abundance, annual nest-site distribution, and nest distribution among tree species. We estimated that there were 6 or 7, 8 or 9, and 6 or 7 breeding pairs in 1997, 1998, and 1999, respectively. Of the 26 nests found, 12 (46%) were next to the Rio Grande and 7 (27%) were at the edge of a major wetland within the refuge. Only 1 of the other 7 nests was more than 115 m inside the refuge. Nests (n = 26) were distributed among Salix nigra (39%), Fraxinus berlandieriana (23%), Acacia minuata (19%), Celtis laevigata (8%), Ulmus crassifolia (8%), and Chloroleucon, ebano (4%). Comparisons of results with historical accounts suggest a decline in annual breeding abundance and nest-site availability at SANWR since the early 1970s.