Winter World_ The Ingenuity of Animal Survival - Bernd Heinrich [109]
Gray jays begin nesting in March, about two months earlier than their cousins, the blue jays. At that time in late winter in the Northern Hemisphere, and on high mountains, they can still expect numerous snowstorms and days of subzero temperatures, if not weeks of subzero nights. So aside from sticky saliva, the next critical component of their energy strategy is nest construction. Unlike the blue jay’s flimsy see-through nests of bare twigs and rootlets, those of the gray jay are bulky, deep, and well-insulated cups lined with fur and feathers that cradle and keep warm the clutch of three or four grayish, olive-brown-spotted eggs.
The early nesting by the jays must have an advantage. We don’t know for sure what it is, but a study by Dan Strickland in Quebec and Ontario provides clues. Gray jays may seem like very friendly birds because they readily approach humans, and Strickland (1991) found their nests by offering the birds prized nesting materials, primarily cotton, facial tissue, and grouse feathers, and then following them. From a study of 470 color-banded nestlings in 179 nests he found a surprising social structure centering on food caching.
In Quebec, food caching for winter by a resident pair of gray jays starts in late summer when food is most abundant, so caching then makes sense. With plenty of food available and little or no competition for food, most corvids are then tolerant of each other, especially toward family members. But not gray jays. Strickland was surprised to see constant aggression and chasing of the juveniles within the family group. The result of that intrafamily strife was almost invariably that only the most dominant of the brood remained in the parents’ territory. (Those that left sometimes joined up with other pairs whose breeding attempts had failed.) It was not clear why the parents should tolerate a freeloading offspring all winter, but some evidence (Waite and Strickland 1997) suggests that the lone stayer eventually pays its due by helping at the nest in the parents’ next nesting attempt. Besides, parenting is always costly. And parents have to do whatever is necessary for the offspring’s survival. But why would a young bird fight with its siblings almost to the death to be able to stay with its parents?
Gray jay “gluing” food onto tree.
To survive the coming winter, the young need to store up food. However, young corvids, like the young of most other birds, require experience to become good foragers and cachers of food; especially those that like gray jays and ravens may learn to forage for rather “exotic” fare, such as the blood-engorged ticks that ingest moose blood in winter (Addison, Strickland, and Fraser 1989). Possibly, young gray jays are too inexperienced and cannot quite find and lay up enough food to survive the winter, and so their only chance of surviving is if they can rely on a partial winter subsidy from their more-skilled parents. If so, then the parents are obliged to provide it, or they lose their genetic investment.
The parents, however, are also limited by food and they can’t shortchange future reproduction. They can perhaps support one freeloading youngster through the winter, but not three to four survivors of a full clutch of eggs. If all of the clutch survived, if all of the young of any one clutch stayed, then the whole family could starve. Thus if brood reduction in the winter is inevitable, then it’s better to force a fight and make it happen in advance of the food crunch. The evicted subordinates