Red-crested Cardinals use color and width as cues to reject Shiny Cowbird eggs

SEGURA, LUCIANO NOEL; DI SALLO, FACUNDO GABRIEL; MAHLER, BETINA; REBOREDA, JUAN CARLOS

AUK

AMER ORNITHOLOGISTS UNION

Año: 2016 vol. 133 p. 308 - 315

0004-8038

As part of the coevolutionary process between brood parasites and their hosts, the latter have developed differentstrategies to discriminate and reject parasitic eggs. This recognition?rejection process is the primary host defenseagainst costly brood parasitism. The Red-crested Cardinal (Paroaria coronata) is an occasional host of the generalistShiny Cowbird (Molothrus bonariensis) that successfully rejects all parasitic eggs. We studied the cues used by RedcrestedCardinals to recognize and reject foreign eggs by experimentally adding real parasite and host eggs painted asmimetic or nonmimetic of host eggs and analyzing whether eggshell coloration and/or shape were used as cues foregg rejection. Rejection rates, mostly through egg ejection, were high for all nonmimetic eggs (95% for unpaintedcowbird eggs and 100% for painted nonmimetic cowbird and host eggs). On the contrary, they were low for mimetichost eggs (6% for unpainted host eggs and 20% for painted mimetic host eggs), but intermediate for painted mimeticcowbird eggs (55%). We also found that egg width significantly affected the probability of rejection, with widerparasitic eggs (i.e. more different from host eggs) more frequently rejected. We report for the first time that egg widthis an important cue for recognition and ejection of cowbird eggs in an open-cup-nesting host. Our results show thatcoloration is a reliable cue used by Red-crested Cardinals to discriminate and reject parasitic eggs, but when colorationalone does not allow discrimination of foreign eggs, this host uses egg width as an additional cue.