A temporal shift in Steller's jay predation on bird eggs

Artificial-nest experiments conducted near Juneau, Alaska, indicated that Steller's jays (Cyanocitta stelleri) may undergo a marked shift in foraging pattern and possibly nest-predation behavior triggered by fledging of their own chicks. In an early-June sampling of predation on artificial nests containing quail eggs, egg losses and jay activity levels were significantly higher in forest adjacent to human-created edge than in undisturbed interior forest. In a late-June sampling, however, nest predation near edges was significantly reduced, and this was correlated with a drop in jay activity (detected via predator censuses and remote-controlled camera stations baited with artificial nests). Steller's jays in natural nests monitored during the study fledged their chicks between the two samplings, which suggests that quail eggs were an important food for jays during their nestling period (early June) but not after (late June). Nests in the two plots in interior forest, where jays were rarely detected, had consistently low nest predation rates in both samplings. These data support the hypothesis that during their nestling period, adult Steller's jays in southeast Alaska may prey intensively on the contents of other birds' nests in the vicinity of their own nests, but that fledging of jay chicks abruptly changes foraging patterns, including possibly reducing nest-predation behavior. Given the short breeding season in southeast Alaska, it is likely that during the postfledging period, jay families concentrate on obtaining foods (e.g., conifer seeds) that are more important for over-winter survival of the juveniles than nest contents, which decrease rapidly in abundance during July.