eWestern Birds

Nesting Ecology and Nest Success of the Blue Grosbeak along Two Rivers in New Mexico

Jean-Luc E. Cartron, Deborah M. Finch, David L. Hawksworth, and Scott H. Stoleson

ABSTRACT: From 1997 through 2008, we studied the nesting habits and nest success of the Blue Grosbeak (Passerina caerulea) along the middle Gila River (1997–2001) and the middle Rio Grande (2000–2008) in New Mexico. A riparian forest of cottonwoods grows along both rivers, but the forest along the Rio Grande is a much more intensively managed ecosystem, with an understory dominated by saltcedar (Tamarix spp.) and other non-native invasive plants, frequent wildfires, and large-scale attempts at remediation of the vegetation. Along the Gila River 100 (95%) of 105 nests were in native shrubs or trees, and the mean height of all nests was 3.4 m. Of 85 nests found along the Rio Grande, 54 (64%) were in saltcedar and 16 (19%) were in other non-native shrubs or trees. Mean nest height was 2.2 m, significantly lower than along the Gila River. Nests were typically found along edges along both rivers but were placed significantly farther from water along the Gila River. In spite of these differences in nest placement, the observed proportion of successful nests along the two rivers did not differ significantly: 28 (47%) of 60 nests along the Rio Grande, 36 (54%) of 67 nests along the Gila River.Overall, differences between the two sites in floristic composition and vegetation structure appeared to affect the placement of Blue Grosbeak nests more than they did nest success.

Download—Nesting Ecology and Nest Success of the Blue Grosbeak along Two Rivers in New Mexico