A Four-year Summary of Breeding Bird Surveys in TFL 48 ... - BIOD

Preliminary TrendsAnnual variation in abundance within a species in TFL 48 is most likely attributedto climatic variation among years, and to some extent among different observers usedeach year. Caution should be given to interpreting trends over short temporal scales(i.e., four years).The mean abundance and standard error for 12 regularly occurring species inTFL 48 are given in Figure 10 and Figure 11. Preliminary analyses of trends (2002 –2005) for the 20 most frequently detected species in TFL 48 are provided in Table 1.Two species showed a significant increase (Dark-eyed Junco and Tennessee Warbler),and four species showed a significant decrease (Chipping Sparrow, Gray Jay, RubycrownedKinglet, and Swainson's Thrush). Non-significant differences among pairs ofadjacent years were noted for most species, although overall patterns for the four yearswere either increasing (e.g., Dark-eyed Junco and Tennessee Warbler), decreasing(e.g., Chipping Sparrow, White-throated Sparrow, and Ruby-crowned Kinglet),oscillating (e.g., American Robin, American Redstart, and Swainson's Thrush), or stable(e.g., Warbling Vireo, Yellow-rumped Warbler, Alder Flycatcher, and Lincoln's Sparrow).In TFL 48, from 2002 – 2005, significant and linear decreasing trends inabundance were observed for Chipping Sparrow, Gray Jay, and Lincoln's Sparrow.Significant and linear increasing trends in bird abundance were found for Dark-eyedJunco and Tennessee Warbler. The Golden-crowned Kinglet (stable) and Swainson'sThrush (significant decrease) had non-linear, oscillating patterns of abundance. BothGwillim (in 2005) and Wolverine contribute more to the variability than other transectsbecause of lower sample sizes.17