Riparian Bird Population Monitoring in Utah, 1992-2001
This article is part of a larger document. View the larger document here.Abstract
We report statewide linear and non-linear trends in density from 1992 to 2001 for six common bird species in the riparian areas of Utah. The six species examined here represent over 24 percent of all observations in the period. Four of the six species showed linear declines (Black-headed Grosbeak [Pheucticus melanocephalus], American Goldfinch [Carduelis tristis], American Robin [Turdus migratorius], and Broad-tailed Hummingbird [Selasphorus platycercus]) over this period, but the decline in only one species—the Broad-tailed Hummingbird—was considered significant here (F = 19.45, P = 0.002). Yellow Warbler (Dendroica petechia) numbers showed the only other significant linear trend, increasing significantly since 1992 (F = 15.30, P = 0.004); Song Sparrow (Melospiza melodia) numbers showed a non-significant increase. A parallel analysis, using Generalized Linear Models to identify non-linear patterns in population trends, showed two apparently consistent patterns of population change with synchronous timing of significant trend inflection points. The evaluation of these non-linear patterns, if they persist as additional analyses are competed, will be important to future assessments of Utah's avian conservation needs.