1. The heading, "Dull Colors," includes all shades of gray or olive, very
dull dark-brown and black not showing conspicuous iridescence. Birds in
this group are very rarely streaked or spotted, never barred and seldom
show any trace of bright colors.
2. To make the key compact and to avoid referring to the index the birds
are indicated by their respective numbers as given under "Particular
Hints."
3. Females differing greatly _in coloration_ from the males are denoted
by heavy figures. Differences in markings are taken into account only
when the female is particularly obscure or liable to be mistaken for
another species.
4. Every bird appears once under the first six general headings, and a
few twice, some of which come under apparently contradictory headings in
order to cover incomplete as well as complete observations. For example,
the _Robin_ has a streaked throat and the _Fox Sparrow_ an indistinctly
streaked back, both inconspicuous points, often overlooked in the field,
yet useful if complete observations have been made. Again, the
_Yellow-bellied Flycatcher_, though brighter colored than most of its
kind, would scarcely be described as having either brilliant or very dull
plumage, and is therefore difficult to tabulate exclusively in one place.