REMOVAL OF PINYON SEEDS BY BIRDS AND RODENTS IN SAN-LUIS-POTOSI, MEXICO

Removal of pinon seeds by birds before the period of seed production w as higher on a northeast-facing slope (as opposed to a level area and a southwest-facing slope), probably as a result of better perches. Arr ival of migrant birds after the period of seed production eliminated d ifferences in seed removal. Removal of pinon seeds by rodents was high est on the southwest-facing slope due to higher densities of Peromyscu s. On clear nights, rodents foraged preferentially near the base of th e trunks. In captivity, one Peromyscus difficilis and one P. maniculat us preferred pinon seeds from Pinus cembroides over those of P. discol or and rejected empty seeds.