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Jays: Foraging and families

Posted: October 28, 2011 - 12:01am
Jay with egg.  Courtesy of Mary Willson
Courtesy of Mary Willson
Jay with egg.

T here is a gang of four Steller’s jays that constantly visit my seed-feeders. I assume (on no real basis whatsoever) this Gang of Four is a group of siblings, progeny of the pair that brought them to my feeders in the first place. Back then, they were scruffy, clumsy youngsters, with short crests and the remnants of a pinkish flange at the corner of the bill. Then, one day in October, the noisy foursome was joined by two others, perhaps their parents. According to official accounts, Steller’s jay families often stay together into fall and winter. On the other hand, sometimes rich food sources attract numerous jays; a friend who puts out peanut treats has recorded more than a dozen jays at a time.

There are more than 40 species of jay in the world (every continental area except southern South America, Australia, and of course Antarctica), occurring mostly in wooded habitats. Many of them have not been studied very much. Two of the better-studied North American types are several kinds of scrub jays, in the southern U.S., and the distantly related gray jay, which is widespread in boreal forests. These two offer striking contrasts to the family relationships of Steller’s jays.

Scrub jays are known to be “cooperative breeders,” meaning young birds commonly remain on the parental territory and help care for the next year’s broods. So, many scrub jays don’t mature and breed until they are 2 years old. Gray jays were long thought to lack such helpers. A dominant fledgling drives out its subordinate siblings two or three weeks after they leave the nest, and the dominant stays on the parental territory until the early in the next nesting season, when it too is driven out by the parents. Both dominant and subordinate siblings then must find their own mates when they are about 1 year old. However, later observations showed sometimes the dominant young bird helps the parents rear the next year’s brood, but doing so only after the young chicks leave the nest. Then they may feed and guard the fledglings for a few weeks. Thus, some gray jays mature at age 1, as previously thought, and others wait until age 2.

Steller’s jays are less well studied than scrub jays or gray jays. But as far as is known, the family breaks up over the winter, the young birds do not help raise the next year’s brood, and they mature and mate at age one.

What determines these differences in family arrangements? That’s a subject of considerable debate. One important factor is probably the size of the population in relation to the amount of available habitat: when habitat is limited, it is harder for dispersing young birds to find their own space, and then it pays for them to stay home and help rear their young siblings.

All North American jays cache food, on the ground or in a tree. They use landmarks, such as a tuft of grass, a stone, or a clump of lichen on a branch, to re-locate food they have hidden. They are good at remembering these landmarks and have high retrieval rates if the landmarks are not disturbed. Gray jays can cache several hundred food items per day. These jays generally gum down their stashes with sticky saliva and use the stored food through the winter and even into the next nesting season. They are unusual in that they often carry large food items in their feet; they can carry items weighing 50 or 60 percent of their body weight (60 to 80 grams). Other jays apparently do not do this, although Steller’s jays have sometimes been observed to attack and grab small songbirds with their feet, and then transferring the catch to their bills.

Because of their extensive food caches, a gray jay can start nesting very early in the season, in February and March when snow is still falling. I haven’t found much information on food caching by Steller’s jays (beyond the fact that they do so), but we do know that they are somewhat early nesters too — but not as nearly as early as gray jays.

The reasons for early nesting have been debated, with no resolution in sight. One interesting suggestion is that both gray jays and Steller’s jays often feed on the eggs and nestlings of other birds, so they produce their own chicks in time for the season when those food sources are plentiful, in late spring and early summer. Here in Juneau, we found that Steller’s jays seemed to concentrate their nest-raiding while their own chicks were still in the nest, and did so less after their chicks had fledged.

In Atlin, we watched gray jay families, with young fledglings, moving through the shrubbery as a group, as if they were searching for nests to raid, or at least teaching the young how to do so. A gang of jays jumping around in the foliage would certainly tend to flush any incubating or brooding songbird parent from its nest, exposing the contents and calling attention to the nest area.

However, I don’t know if they are really searching specifically for nests — a study of Steller’s jays in Washington suggested they find nests opportunistically, not as a result of a concerted search just for nests. There is always more to be learned!

• Mary F. Willson is a retired professor of ecology.

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