This fall we have a big crop of tan oak acorns, the most I have seen in the five years I have lived here. These trees have large leaves with noticeable “ribs” (veins). The acorns are very big and are a favorite food for wildlife. I also noticed that our acorn woodpeckers are busily stuffing acorns in holes and cracks all over the reserve. These amazing creatures are highly dependent for survival on acorns, which they store in large “granaries” or storage trees. During the fall and winter months they eat the intact acorns for food (they do not store acorns in order to eat the insects inside, as is commonly supposed). Their complex social life centers on ownership and defense of these granaries, which must be protected against other colonies of woodpeckers, jays, squirrels, and other animals. Researchers at Hastings Natural History Reservation in Carmel Valley have devoted many years to detailed study of these animals.This month I also noticed that the acorn woodpeckers seem to have (temporarily?) abandoned their usual “granary” trees. Feynner (our reserve steward/naturalist) and I speculate that perhaps they have abandoned the central granaries in favor of gathering the tan oak acorns as rapidly as possible. Getting them up off the ground and jamming them in cracks (as we have observed) would save them from many would-be acorn eaters such as deer, wild pigs, quail, and band-tail pigeons. We will be watching to see if the acorns are subsequently moved to centralized granaries where they can be defended.
This year’s tan oak acorn crop is another example of mast fruiting, (like the Santa Lucia Fir). Oaks are well-known “practitioners” of mast fruiting. In this case, the activities of the woodpeckers illustrate how mast fruiting may benefit the oak trees. If our speculations are correct then the woodpeckers are responding to the large “mast” crop by spreading acorns away from the parent trees and protecting them from immediate consumption on the ground. During the process of transport and storage many acorns probably get lost and fall to the ground, and thus have the opportunity to germinate and survive.
Last October 11 swarms of flying ants and termites made their appearance. These winged “reproductives” leave the home colonies and usually do not return. Once airborne, their goal is to mate successfully and found a new colony. Derek Sikes, a researcher working at Big Creek, reported swarms the same evening in the Santa Cruz mountains. The swarming was almost certainly triggered by the thunderstorms during the day. These insects frequently synchronize their mating flights by responding to thunderstorms and other dramatic weather events. In this way they increase the probability of encountering potential mates. (10/15/91)