Screaming Cowbirds can relocate a food source, learnt by using color and positional cues, using only positional cues

Screaming cowbirds (Molothrus rufoaxillaris) are socially monogamous obligate brood parasites that search and locate host nests during daytime and return to these nests one or several days later to lay eggs in the pre-dawn twilight. Visual cues, and especially chromatic information, are thus extremely different between daytime prospecting and twilight laying nest visits, posing the question of what stimulus dimension predominates in the birds relocalization memory. We trained six females and four males Screaming Cowbird to locate a food source using color and positional cues and evaluated their performance relocating the food when the color cue was no longer informative. Training and testing were conducted in an experimental arena with 36 holes, each one covered by a sliding brown disk. During the acquisition, the well with food was always in the same location, which was indicated by a red disk. After birds learned this location, the color and positional cues were dissociated (the food remained in the same location, but the position of the red disk varied randomly among holes). There were no sexual differences in the acquisition and the dissociation. Most females and males followed initially the color information but they made fewer errors to find the food location than expected by chance, which indicates that they remembered the positional cue. Our results show that females and males Screaming Cowbird can relocate a food source that was learnt using color and positional cues using only positional cues.