[讨论]GWD 25-13~15

Grassland songbirds often nest in
the same grassland-wetland complexes
as waterfowl, particularly in a certain
Line part of those complexes, namely,
(5) upland habitats surrounding wetlands.
Although some wildlife management
procedures directed at waterfowl, such
as habitat enhancement or restoration,
may also benefit songbirds , the impact
(10) of others, especially the control of
waterfowl predators, remains difficult to
predict. For example, most predators
of waterfowl nests prey opportunistic-
ally on songbird nests, and removing
(15) these predators could directly increase
songbird nesting success. Alterna-
tively, small mammals such as mice
and ground squirrels are important
in the diet of many waterfowl-nest
(20) predators and can themselves be
important predators of songbird
nets. Thus. Removing waterfowl-nest
predators could affect songbird nesting
success through subsequent increases
(25) in small-mammal populations.
            

这句话不知道在搞什么鬼....移除水鸟侵袭者要透过增加地鼠?
地鼠不是也会侵袭唱歌鸟的巢吗?完全逻辑接不上...
还有上面的Alternatively代表什么意思?在前后两句的功能是什么?

In 1995 and 1996, researchers
trapped and removed certain waterfowl-
nest predators. primary raccoons and
striped skunks, then observed subse-
(30) quent survival rates for songbird nests.
Surprisingly. They observed no sig-
nificant effect on songbird nesting
success. This may be due to several
factors. Neither raccoons nor striped
(35) skunks consume ground squirrels,
which are important predators of song-
bird nests. Thus, their removal may
not have led to significant increases
in populations of smaller predators.
            

这边更奇怪了~~移除浣熊和地鼠增不增加有什么关系?
而且这和水鸟不能成功筑巢也扯不上关系?

(40) 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.

真的看不出来作者到底想说什么...有人能解释一下吗?

 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.第一，移去predator可以增加成功率，第二alternatively移去predator增加mammals从而降低成功率

     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.

实验结果surprising。

作者解释为： raccoon和skunk不吃squirrel（small mammal），不满足上述第二条，raccoon很少去upland吃songbird, 不满足第一条