A paper published in a scientific journal describes how Black-capped Chickadees and Red-breasted Nuthatches weigh sunflower seeds before flying off to consume them! You may have noticed that some species sit at the feeder to eat (finches, sparrows, woodpeckers) while others retrieve a seed from the feeder and fly to a safer, nearby branch to consume it (chickadees and nuthatches). In this particular experiment, the birds were offered three choices: normal stripe sunflowers, ones from which the kernels had been removed, and ones where the kernel was replaced with heavier plaster of Paris. In the case of both “altered” seeds, the two shell halves were re-closed so the seeds appeared normal. The results demonstrated that chickadees and nuthatches selected the heavier seeds over the lighter ones. We can only feel for the poor nuthatch that dropped the good sunflower seed to fly off with the plaster filled one, for the sake of science! The assumption is that flying to and from a feeder costs time and energy, and involves some risk. Therefore, maximizing the calories gained during each foray is important The chickadees and nuthatches visiting your feeders are discriminating between, and availing themselves of, the very best seeds! The striped sunflowers used in all Aspen Song mixes are called “medium hullers” and are a grade above what is generally traded as “bird food smalls.” They are larger, plumper, and heavier. We choose to discriminate because the birds do!
Heinrich, Joerg, Madden and Sanders. 1997. Blackcapped Chickadees and Red-breasted Nuthatches “Weigh” Sunflower Seeds. The Auk 114(2):298- 299.