ILLINOIS AUDUBON BULLETIN 23 
be problems. I once set out to memorize all the important field marks for all the 
species in Peterson’s guide. I thought that would be a panacea for all my field 
problems, and I'd be able to identify every bird from then on. My intentions were 
good, but naive because field guides are limited out of necessity by their format. 
Guides do not have the space to illustrate or discuss all of the female, immature, 
and juvenal plumages, or the range of variation in each species. Furthermore, I 
know of no guide that is free from errors of fact, of omission, or of emphasis. 
Let me give two examples that show why you have to go beyond the field 
guides in order to become a more expert observer. 
1. The Rough-legged Hawks shown in the field guides are typical first- 
winter birds. But there are adults and young of both light and dark phases, as 
well as intermediate forms. Furthermore, there is a great deal of variation even 
within any one of these types. So many individuals appear appreciably different 
from the illustrations, and are either left unidentified, or are identified as other 
species. (I believe that some of the ‘‘Harlan’s Hawks’’ reported in this journal 
have been Rough-legged Hawks.) However, if you have access to an ornitholo- 
gical library and a good specimen collection, you can learn enough about this 
species’ plumages to be able to identify correctly almost all the Rough-legged 
Hawks you will see. (A future article will discuss this species.) 
2. One of the field guides says, in reference to Barrow’s and Common 
Goldeneyes, ‘‘In the winter it is not safe to tell females except by the males they 
are with.’’ In fact, female Barrow’s Goldeneyes can be. distinguished from 
female Common Goldeneyes even in flight, if you know what to look for and 
have the necessary experience. Unfortunately, one can’t get that experience in 
Illinois. 
Before someone gets the impression that I’m knocking the field guides, let 
me say most emphatically that I’m not. They have to be any birder’s primary 
identification aid. They’re adequate for the vast majority of the birds you see, but 
other sources will have to be consulted for those few that give you problems. 
What sources? I’ve already mentioned other ornithological references and a 
specimen collection. But most important is your own careful observations over a 
long period of time. If you have learned to take field notes from careful 
observations, you can always turn later to other references and collections to 
identify a bird. And if you have the patience to make careful and critical 
examination of birds you see in the field, you may even discover new identifi- 
cation marks. One day, for example, I sat for a long time looking at a mixed 
flock of scaup in Chicago Harbor, looking for differences in every portion of the 
plumages and soft parts. To my surprise, I found a completely reliable, 
diagnostic mark, easily seen from as far as 200 yards, for separating adult male 
Greater and Lesser Scaup. I have never seen it mentioned in any reference. 
(More on that in a later article.) 
