The "height of the migration" usually comes during the second or third week in May. This chart makes a comparison of the observations of six years graphic.

For instance, the largest number of different species seen on any one morning in 1903 was 68 (May 12), while in 1901 it was 48 (May 16).

The sudden rise or fall in the migration may also be seen at a glance.

May 9, 1899, for example, only 16 different species were observed and May 10 the record was 40. Similarly, in 1901, the number of species seen May 17 dropped from 45 to 15 in three days.

A chart showing the number of different kinds of birds seen in _LINCOLN PARK_ during the _HEIGHT OF THE MIGRATION_

Note to Key.

In response to many demands, the following simple field-key has been devised, to the end that the beginner may be aided in learning to observe correctly those points about a bird that appear most conspicuous in the field or which are particularly distinctive.

Technical a.n.a.lyses and measurements have not been employed, but instead, the birds are roughly placed in three groups according to size, the Robin and English Sparrow marking respectively the 10-inch and 6-inch lines of division.

The first part of the key deals with _general_ differences in color and markings, while the second seeks to emphasize the most noteworthy _special_ points which distinguish the different species. Incidentally a few striking peculiarities of bill, wings and tail have been included.

It will readily be seen that a key embracing so little cannot do more than reduce wild guessing to a few reasonable chances in identifying a strange bird. Some practice is of course necessary to enable the student to use the key readily. Its helpfulness will largely depend upon accuracy of observation and a careful application of the points which it suggests.

Sh.o.r.e and water birds have been omitted--first, in order to keep the key as simple as possible; second, because quite full descriptions of these birds are given in the "Particular Hints;" and, third, for the reason that beginners, as a rule, meet with far better success by becoming familiar with the common land birds before attempting the study of water and sh.o.r.e birds.

EXPLANATIONS.

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.

HOW TO USE THE KEY.

Two ill.u.s.trations will most briefly indicate the easiest method of using the key--

_Observation:_ A dull-colored bird of medium size, nearer six inches than ten, much streaked all over, showing nothing distinctive unless a kind of spot on the breast. Turning to the key, pa.s.s by "_Bright Colors_,"

"_Iridescent_" and "_Dull Colors_," choosing "_Streaked, Barred or Spotted._" Not being sure of the size, it may be necessary to try all the birds between "6 and 10 inches," as well as those "less than 6 inches."

Before going to so much trouble, however, pa.s.s on to "_Under Parts_" and see whether an easier approach can be made there. The sub-heading "Spot or patch on throat, sides, breast or sides of neck" looks comprehensive enough to apply, while in this case it contains fewer examples. Comparing the numbers there given with those under the first heading selected, it is found that only 10 and 23 appear in both places. On looking up 10 and 23 it is found that they refer to the _Song Sparrow_ and _Sapsucker_, two species so widely different in coloration, habits and movements that it ought not to be necessary to study the key further in order to be sure of the bird in question--namely, the _Song Sparrow_.

_Observation:_ A bird in flight, pure white below, without doubt over 10 inches on account of its long tail. Not having seen the general color with any certainty, but being fairly sure of the white breast and long tail, try "Under Parts" first. Only two birds over 10 inches are given under the sub-heading "Pure white or ashy," and these are 103 and 109.

Turning to "Tail," both numbers appear under "very long, sometimes keeled or forked," but only 103, the _Yellow-billed Cuckoo_, comes under "Outer tail-feathers conspicuously white or spotted." _If conspicuous tail spots had been seen_ the key would have helped to identify the bird, but the key alone cannot make up for lack of observations.

The second ill.u.s.tration may give force to the suggestion that certain birds can be satisfactorily identified only after very careful observation and some further study.