28 THE CONDOR Vol. XV local breeding places at least may not be fixed from year to year. There is con- siderable shifting, this irregularity ?eing concurrent with varying food supply. To illustrate: in case there has been in a certain mountain range an abun- dant acorn crop, sufficient to last throughout the winter, any flock of pigeons foraging there would be likely to linger on until the advent of the usual season of nesting. These pigeohs would thus be more likely to remain there and breed that particular season, zonal conditions being favorable, than to move off to an- other mountain range. Such an explanation. would appear to account for the vacillating numbers of breeding birds in the various more or less isolated moun- tain ranges of Southern California. RELATIVE NUMBERS, PAST AND PRESENT It has been found practically impossible to estimate relative numbers of pige- ons now as compared with any former period. This difficulty results from the variability from year to year in the degree of concentration of the birds in limited areas, and further from the sporadic distribution at any season. Reports of ob- servers, therefore, no matter how explicit they may appear, cannot be used fairly in such inductions. In fact, no single statement previous to that of Chambers (I912, p. Io8) would lead to the inference that pigeons were ever more numerous than last year. But taking the above considerations into account, no significance can be given to Such isolated statements. The literature examined gives no exact .data; but we can, fievertheless, be morally certain that there has been a very great decrease in the numbers of pigeons since the early days of western settlement, when game of all sorts was so abundant as to arouse but little comment. FOOD o? TI-IE PIGEON As already intimated, the amount of food available to the pigeon appears to be the main controlling factor in distribution, aside from zonal considerations. This is more particularly true in winter, though probably to some extent in sum- mer also.. As will be observed from the following data, the food consists chiefly of berries and nuts, of intermittent productiveness. A large crop one year.in a certain region is almost sure to be followed by a barren year. So that the pige- ons would fare poorly if dependent closely on any one single locality. Their pro- clivity for circulating over large areas makes available to them the abundant crops recurring at different places. The birds in great numbers are thus' able to find support somewhere all the time. Out of twenty-two records, ten give acorns as the chief article of diet. Prob- ably all the species of oaks are patronized by the pigeons. Those especially re- cor?ded are: in west-central and southern .California, the live oaks (Quercus agri- [olia and Q. wlslizenli), in the foothill regions, the golden oak (Ouercus chryso- lepis), and along the Sierra Nevada and on the San Bernardino and San Jacinto mountains, the black oak (Ouercus kelloggii). The acorn season lasts well through the autumn months, and under favorable circumstances even until Feb- ruary. As with all other food, the acorns are swallowed whole in such numbers that the crop becomes at feeding time enormously distended. In this dilation of the gullet the food is acted upon by the powerful digestive juices, and both shell and kernel rapSdly disintegrate and pass on to the stomach and gizzard. There is no disgorgement of hard parts of the food, as with some birds. Considering the ap- parent small size of a pigeon's mouth, an amazing thing is its ability to swallow
