Supplemental feeding and dawn singing in black-capped chickadees

Abstract

The dawn chorus is a collective behavior involving a network of birds signaling at the same time. Two hypotheses can explain the mechanisms of dawn singing. The "condition-dependent hypothesis" states that the dawn chorus consists of a "broadcast network" in which the signal is given in all directions but is not dependent on the singer's neighbors' chorus. The song output is condition dependent and can thus be limited by the amount of food to which a signaler has access to in its territory. On the other hand, the "social-dynamic hypothesis" states that during the chorus the birds are constantly interacting with their neighbors. Under this scenario, the dawn chorus consists of an "interactive network" and the song output is not dependent on the condition of the signaler but on the interaction with the neighbors. To determine which scenario best explains the mechanisms of the dawn chorus in the Black-capped Chickadee (Poecile atricapillus), we set up a supplemental-feeding experiment in a dyadic fashion by providing 3.5 g of mealworms to selected birds and compared their song output to that of unfed counterparts by controlling for rank and habitat. We found that fed birds, both dominant and subordinate males, sang more than unfed birds. We thus conclude that body condition is a critical variable contributing to individual differences in song output in the Black-capped Chickadee and consequently the functioning of the dawn-chorus network. © The Cooper Ornithological Society, 2009.