| Grassland songbirds often nest in the same grassland-wetland complexes as waterfowl, particularly in a certain part of those complexes, namely, upland habitats surrounding wetlands. Although some wildlife management procedures directed at waterfowl, such as habitat enhancement or restoration, may also benefit songbirds, the impact of others, especially the control of waterfowl predators, remains difficult to predict. For example, most predators of waterfowl nests prey opportunistically on songbird nests, and removing these predators could directly increase songbird nesting success. Alternatively, small mammals such as mice and ground squirrels are important in the diet of many waterfowl-nest predators and can themselves be important predators of songbird nets. Thus. Removing waterfowl-nest predators could affect songbird nesting success through subsequent increases in small-mammal populations.
In 1995 and 1996, researchers trapped and removed certain waterfowl-nest predators, primary raccoons and striped skunks, then observed subsequent survival rates for songbird nests. Surprisingly. They observed no significant effect on songbird nesting success. This may be due to several factors. Neither raccoons nor striped skunks consume ground squirrels, which are important predators of songbird nests. Thus, their removal may not have led to significant increases in populations of smaller predators. Additionally, both raccoons and striped skunks prefer wetlands and spend little time in upland habitats; removing these species may not have increased the nesting success of songbirds in the uplands enough to allow detection.
请教牛牛， 请教牛牛，
第一段黄色的部分意思是waterfowl-nest-predator吃mice and squirrel, 然后mice and squirrel吃songbirds.那为什么thus后面说可以通过减少waterfowl-nest-predator来增加mice and squirrel使songbirds nesting success呢？mice and suqirrel增加了，songbirds不就更遭殃了么？？
并且第二段success songbird nest的试验中，thus后面又说remove raccon and skunk没能增加smaller predator的数量。好像增加smaller predator的数量可以使得songbirds nest success.这是什么逻辑啊？读了好几遍都不明白~~求大虾指教，万分感谢。 | 
