156 NEW YORK ZOOLOGICAL SOCIETY. 
among birds. These creatures, handicapped by a vocal language 
very inferior to our own, and faces, for the most part sheathed, 
like those of insects in expressionless masks of horn, yet are 
able by movements of their feathers, limbs, and other portions 
of the body, to express a wide range of emotions, and to clearly 
communicate even delicate shades of meaning. 
Interrupting, for a moment, the mention of these finer quali- 
ties which show the high mental position of birds, it is desirable 
to emphasize a factor common to all animals, but which in birds 
is very important, and developed to a remarkable degree—that 
of extreme individuality. It is to this plasticity or wide varia- 
tion on the already high level of knowledge or “platform of 
determination,” as Baldwin happily terms it, that gives to birds 
the numerous chances for new accidental opportunities, as we 
may call them—stepping-stones on the road of deduction, to 
some new and higher expression of psychic power. Every-day 
accidents in the search for food may be instantly seized upon 
by the quick perception of birds and turned to good account. 
Birds had early learned to take clams or muscles in their beaks 
or claws at low tide, and carry them out of the reach of the 
water, so that at the death of the mollusk the relaxation of the 
adductor muscle would permit the shell to spring open and afford 
easy access to the inmate. Probably itsneeded only the accidental 
dropping of a few shells on the hard rocks, and a taste of the 
appetizing morsels within, to fix the habit which, by imitation, 
has spread so widely among birds at the present day. To how 
trivial an accident might the beginnings, the psychic anlaga, of 
many modern cosmopolitan traits of birds be traced if we could 
but read the past clearly! 
Play and courtship—while they go hand-in-hand, so to speak 
—afford opportunity for the vast resources of variation to be 
abundantly expressed. Groos, in his admirable “Spiele der 
Thiere,” has given five separate classes under the head of court- 
ship: 
1. Love plays among young animals. 
2. Courtship by arts of movement. 
3. Courtship by display of unusual or beautiful colors and 
forms. 
4. Courtship by means of noises and tones. 
5. Coquetry in the female. 
In the Zoological Park each spring, and indeed during almost 
every month of the year, many examples of these courtships and 
plays can be observed. The dances of cranes and eagles, the 
