Most passerine birds practice nest sanitation whereby they remove debris from their nest. Nest sanitation has been posited as a pre-adaptation for egg ejection by hosts of avian brood parasites. However, relatively few North American hosts of the brood parasitic brown-headed cowbird (Molothrus ater) eject cowbird eggs to the detriment of their fitness. In this study, I added either a piece of flagging tape or a pine cone bract scale along with an artificial cowbird egg to nests of the red-winged blackbird (Agelaius phoeniceus) to determine whether the act of nest sanitation would elicit egg ejection. All red-winged blackbirds removed the debris within 24 h, but all individuals also accepted the cowbird eggs and this rate of ejection did not differ from that in nests that only received a cowbird egg. While nest cleaning and egg ejection are similar mechanically, they differ cognitively and egg ejection is not elicited in red-winged blackbirds during the act of removing debris from their nests.
Keywords: Brood parasitism; Brown-headed cowbird; Egg ejection; Nest sanitation; Red-winged blackbird.