soils. Singing voles and red-backed voles also were commonly captured in all 

 regions. Most singing voles were captured in habitats that were more removed 

 from the active portions of the floodplains, while red-backed voles were 

 most abundant in the mature spruce-birch forest of the Interior sites. 



The most important aspect of clearing advanced and mature shrub thick- 

 ets and spruce-birch stands was the loss of feeding, nesting, and cover 

 habitats for passerines and smal I mammals. No sma I I mammals were observed or 

 captured in unvegetated or sparsely vegetated portions of disturbed areas at 

 any of the 25 study sites. Also, passerines displayed no direct association 

 with these areas, and only were observed on a few occasions feeding or 

 drinking in these habitats. As identified in previous sections, character- 

 istics of the gravel removal operations and subsequent hydraulic changes 

 most frequently resulted in long-term loss of terrestrial habitats. Thus, 

 the local passerine and smal I mammal populations, primari ly at the larger 

 sites, most likely were significantly reduced as a result of lost habitat. 



Population Increases 



At some sites the gravel removal operation created habitats that were 

 more desirable to some species than pr ed i sturbance habitat conditions. 

 Population levels of water birds (including waterfowl, shorebirds, gulls, 

 and terns) increased within the disturbed area at 12 sites (Table 28). These 

 sites included those where mining resulted in permanently ponded areas (such 

 as Jim River, West Fork Tolovana River, or Tanana R i ver-Upstream) and where 

 mining removed dense vegetation creating ponded water or backwater areas 

 and/or mud flat and gravel bar habitats (Penny River and Aufeis Creek). 

 These habitats provided the preferred feeding and nesting areas for these 

 birds. 



Many of the most significant increases occurred at sites where the 

 adjacent upstream and downstream floodplain was heavily vegetated, and the 

 gravel excavation provided habitats that were not readily available in the 

 immediate floodplain vicinity (Penny River, West Fork Tolovana River, and 

 Tanana R i ver-Upstream) . Birds that were most frequently associated with 

 gravel and mud flat habitats in material sites included semipalmated 



25 1 



