ANIMAL BEHAVIOR—ERNEST P. WALKER 281 
insects and fruits become scarce and many of the birds cannot survive. 
By migrating to regions farther south, however, they are able to 
obtain an adequate supply of such food. Some forms that do not 
migrate change their feeding habits during the year. During the 
summer when fruit and insects and other animal life are abundant and 
easily obtained, they feed extensively on these elements, and in the 
winter they eat seeds and plant life that has matured during the 
summer. Good examples of this are the birds of the sparrow group 
(Fringillidae), in which the young are fed almost exclusively on insects 
and fruit and the parents eat such food extensively when it is available, 
but during the winter when few insects or fruits are to be had, they 
feed mainly on seeds. Others feed only on certain types of food and 
apparently cannot survive unless they can obtain these particular 
foods. Notable among these are the cross-bills (Loxia), birds of the 
Northern Hemisphere about the size of sparrows with usually some 
bronze, red, or purple markings. They feed on seeds of the spruce, 
hemlock, or pine which they obtain directly from the cones by perch- 
ing on them and reaching under the scales of the cones with their 
peculiar crossed mandibles and extracting the seeds. Such beaks 
are probably well adapted for this purpose but are a serious handicap 
to eating the type of food that most birds consume; therefore these 
birds are erratic in their occurrence in a given range. If there is a 
failure of the seed crop of the spruce, hemlock,-or pine, they must 
move to regions in which there is a good crop of seeds on these trees. 
Such sturdy, hardy animals as the American bison (Bison bison) 
and caribou (Rangifer) have extensive ranges that embrace both 
summer and winter forage grounds to which the animals migrate 
seasonally, some making a round trip of several hundred miles each 
year, measured in straight lines. 
We are prone to think of our food selection and handling as being 
superior to that of animals, but after observing the care with which 
animals select the choice morsels and pass over food that they detect 
as being contaminated or not palatable to them, I believe that the 
wild ones probably are far better fed and are better judges of food 
than we are. Studies of the feeding habits of antelopes on the native 
range disclose that in a 14-day period they eat 24 to 30 different kinds 
of vegetation. Possibly some of the material was eaten as many of 
us have taken food during war time, merely for the purpose of survival, 
but obviously they picked and selected foods that they preferred and 
thought were best for them. If one will watch a wild rabbit or almost 
any wild animal, he will see that it constantly and carefully selects 
or rejects food. On many occasions I have endeavored to induce 
animals, either wild or in captivity, to eat food that I had seen them 
pass over. Rarely could I get them to do so, and on one occasion, 
