Fig. 20.—Site of cliff swallow colony on the Apple River in Jo Daviess County. A cluster of (darkish) nests may be seen on the 
in the foreground, left of center. 
Fig. 21.—Close-up of cliff swallow colony showing birds at their retort-shaped nests. One nest (center bottom, with bird facing) 
the shell only about half completed. Note pale rump of bird in flight; this is a field mark of the species. 
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