科研之友
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摘要
Oaks (Quercus spp.) rely on vertebrates for seed dispersal. However, the extent to which dispersal is facilitated depends on the vertebrate species involved, its preferences for acorns of different species, and the relative availability of acorns. We examined foraging preferences by free-ranging individuals of four species of birds for acorns of white (Q. alba), black (Q. velutina), and pin (Q. palustris) oak. We photographed selection of acorns at feeding platforms and used discrete-choice models to estimate preferences. Blue Jays (Cyanocitta cristata) had strong and consistent preferences in the order pin oak > black oak > white oak, whereas Red-bellied Woodpeckers (Melanerpes carolinus) exhibited the same but weaker preferences. On the basis of acorn's chemical and physical attributes, these birds appear to focus on maximizing the net value of cached food. Tufted Titmice (Baeolophus bicolor) and White-breasted Nuthatches (Sitta carolinensis) preferred acorns of both pin and white oak over those of black oak. These smaller birds may be limited in their ability to crack harder shells. Our analysis also suggests that competition for limited food resources can lead to instances in which the dominant food item selected is not the most preferred. Ecological studies of oak dispersal and recruitment should consider the role of food preferences by avian assemblages in conjunction with spatial and temporal variation in acorn availability.
- 出版日期2013-11
