Graduate Thesis Or Dissertation
 

Habitat characteristics associated with abundance of band-tailed pigeons and use of mineral sites in the Pacific Northwest

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  • Index counts for the Pacific Coast race of the band-tailed pigeon (Columba fasciata monilis) have declined by -2% per year since survey efforts began in the 1950's and 60's. Mineral sites, important resources with high ion concentrations, are regularly visited by band-tailed pigeons which nest in surrounding forest lands. I used both ad hoc measurements of mineral site characteristics and composition and configuration of habitat types adjacent to mineral sites to develop models predicting band-tailed pigeon abundance at mineral sites, in the Pacific Northwest. Band-tailed pigeons were counted weekly during the summers of 2001 and 2002 at 20 mineral sites. Since, many mineral sites have been abandoned by band-tailed pigeons, I tested for an association between land use types mineral site use by band-tailed pigeons using a database of 69 currently used and 20 historically used mineral sites in Oregon. Lastly, I investigated the association between the timing and duration of precipitation on index counts of band-tailed pigeons at 20 mineral sites. Abundance of band-tailed pigeons was positively associated with habitat dominance, (i.e. 1-Shannon's Evenness or homogeneity of landcover types) at a scale larger than band-tailed pigeon home range size and with distance to the nearest adjacent mineral site. Both a quadratic effect of latitude and use of an indicator variable for regional variation in abundance were also present in top ranked models. Both latitudinal effects predicted an increase in birds from central Oregon to southern Washington, then a decrease from central Washington to British Columbia. My findings suggest that: 1) large areas of homogeneous landcover are important for band-tailed pigeons, 2) distribution of mineral sites is associated with the abundance of band-tailed pigeons, and 3) relative density of band-tailed pigeons in the Pacific Northwest exhibits a latitudinal gradient with more birds counted near the middle of their breeding range. Use of mineral sites in Oregon by band-tailed pigeons was associated with both the amount of forest cover (or lack thereof), and the amount of land under either private ownership or under special management to preserve biodiversity. Higher probability of mineral site use was predicted with increasing forest cover and special status land, lower probability of use was predicted with increasing non-forested landcover and private land. Four hot springs in Oregon were known to have once been used by band-tailed pigeons by no longer are, no hot springs are known to be currently used by band-tailed.
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