Acorn Foraging Behavior of Lidth’s Jays Garrulus lidthi during the Ripening Process of Acorns

Abstract

The co-evolutionary relationship between corvid birds and acorn-bearing plant species, through the food hoarding behavior of the former, is well known. However, acorns include chemical defenses, such as tannins, the quantity of which changes during acorn growth. Few studies have attempted to elucidate the utilization pattern of acorns by corvids during the process of acorn ripening. We conducted a study on the acorn foraging behavior of Lidth's Jay Garrulus lidthi, on Amami-Oshima, Kagoshima Prefecture, during the acorn ripening season of 2000–2001. Jays consumed Quercus glauca and Castanopsis sieboldii acorns and utilized many more green acorns than brown ones of both species. The nutrient content did not differ between green and brown acorns or was higher in the former, while the tannin content did not differ in relation to color. This suggests that even green acorns are profitable food resources. While green Q. glauca acorns germinated, green C. sieboldii acorns did not. Consumption of Q. glauca acorns was much higher for C. sieboldii, despite the greater amount of tannin in the former than in the latter. The results of this study suggest that jays are a more effective potential dispersal agent for Q. glauca, than for C. sieboldii.