A state-dependent sex difference in spatial memory in pinyon jays (Gymnorhinus cyanocephalus): mated females forget as predicted by natural history
Author(s):
AIMEE S. DUNLAP*a, BONNIE B. CHEN*, PETER A. BEDNEKOFFb, TOM M. GREENE*, & RUSSELL P. BALDA*
*Avian Cognition Laboratory, Northern Arizona University;
a Department of Ecology, Evolution, & Behavior, University of Minnesota-Twin Cities;
b Department of Biology, Eastern Michigan University
We tested the prediction that female pinyon jays will be less accurate than males at finding their hidden seeds after many months. Pinyon jays rely on cached seeds for survival over the winter, and males provide all food for their mates at the nest. We first tested how well mated jays recovered seeds cached by themselves, their mates, or nonmates. Females outperformed males after one week, but both sexes performed with great accuracy. Males accurately located caches made by their mates; females did not. Next, we compared accuracies of mated males and females after 1 week, 2 months, and 4 months. Females performed at chance after 2 and 4 months; males remained accurate. We tested unmated birds and found that females were accurate at long intervals and that the sexes performed equally in a general spatial ability task. Spatial memory in pinyon jays may depend upon their mated status: mated females tend to forget, whereas unmated females remember.
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Correspondence: Aimee S. Dunlap,
Department of Ecology, Evolution, and Behavior
100 Ecology,
1987 Upper Buford Circle,
St. Paul, MN 55108
DUNL0063@UMN.EDU
Based on differing roles during the breeding season, male pinyon jays (Gymnorhinus cyanocephalus) are predicted to be more accurate than females in recovering cached seeds over long retention intervals. We additionally predict that males should be able to accurately recover caches made by their mates over short and long retention intervals. During experiment 1, we tested the accuracies of the jays' spatial memory at a short retention interval of 5-7 days. We tested their recovery of their own caches and caches made in their presence by their mate and a nonmate of the opposite sex. While females and males found their own caches with similar accuracy, males were more accurate in finding caches made by their mates. Experiment 2 used the same design for caching, but longer retention intervals of one, two, and four months. Males were more accurate than females in the longer month intervals. To test whether differences found indicated a broad difference in spatial cognition, in experiment 3 we tested nonmated male and female jays in an open-field analogue to the radial arm maze. There were no significant effects of sex for task acquisition, accuracies across retention intervals, or patterns of adjacent holes or errors chosen. In experiment 4, we compared nonmated males and females in cache recovery at long internals and found no sex difference in accuracy. Additionally, neither sex was affected by opportunities for memory rehearsal. We conclude that spatial memory in pinyon jays may be a state-dependent trait: females tend to be less accurate after longer intervals when mated than when not mated.
