Jays and seed dispersal

when a predator doubles as a disperser

On a recent hike, I heard a volley of high-pitched screams coming from a thick stand of small spruces just beside the trail. They sounded very much like the cries of a red-tailed hawk, but that bird would be highly improbable in such a place and at this time of year (February). Surely it was a Steller’s jay, which is well-known to mimic redtails and some other birds as well.

That small incident set off some musings about our Steller’s jay and jays in general. Steller’s jays are omnivorous, eating all sorts of things, including bird eggs and nestlings, carrion, insects, seeds, and fruits. I was thinking in particular about their role in seed dispersal; when they eat fruits, the seeds pass through the digestive tract and get deposited, sometimes in a place where they can germinate and grow. The jays share this important ecological task of seed dispersal with thrushes, waxwings, crows and ravens, bears, coyotes, marten, and other animals.

They are also seed predators, along with sparrows and finches, chickadees, squirrels, mice, and others. In this capacity, they raid bird feeders and train humans to offer peanuts. Sometimes they cache their seedy prizes, under a bit of moss or a stick. Peanuts and most seeds offered in seed feeders don’t grow well here, but cached sunflower seeds sometimes produce seedlings in improbable places.

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This seed probably won’t grow. Photo by Bob Armstrong

I don’t know how often our jays consume the seeds of our trees (spruce, hemlock, pine, cottonwood, alder, willow); all of these seeds are small and typically dispersed by wind; they probably don’t offer much nutrition to a relatively large bird such as a jay. However, in more southerly portions of their geographic range, Steller’s jays are known to harvest and cache the seeds of several conifers. Not all of these caches are retrieved, and the seeds germinate, so there the Steller’s jays are contributing (along with other kinds of jays and Clark’s nutcracker) to seed dispersal, a critical portion of a plant’s life cycle.

Steller’s jays are closely related to the blue jays that live in wooded areas of eastern North America. The blue jay is also an omnivore; among its varied dietary items are acorns and beechnuts. Blue jays harvest and cache these items, sometimes several kilometers from the mother trees. They are much better dispersal agents than squirrels, which cache nuts but don’t travel as widely. Researchers think that blue jays were important in the development of northern forests as the Pleistocene glaciers retreated, by carrying nuts northward to ice-free zones and stashing them.

Neither of these jays is as specialized to a diet of seeds as the pinyon jay of the southwestern U. S. or the more distantly related Clark’s nutcracker of the mountain west. Both of these species depend on conifer seeds year-round, even feeding cached seeds to their chicks early in the summer. Both species travel long distances, sometimes many kilometers, to cache their harvested seeds, and both have excellent spatial memories for retrieving those seeds. But, as usual, not all seeds are retrieved and, because they are often cached in good sites for germination, they become important for forest regeneration. As our climate changes, they and other seed-caching birds could facilitate altitudinal shifts in tree distribution.

Without the seed-caching jays and their relatives, some forests cannot regenerate. For example, pinyon pines are dispersed by western scrub jays (along with nutcrackers and pinyon jays). A study in New Mexico, where scrub jays were the main pine-seed dispersers, showed that near a very noisy industrial area, the jays became extremely rare and, correspondingly, there were many fewer pinyon pine seedlings in the forest, while at the same time, in a relatively quiet area, both jays and seedlings were common. Noise pollution drove out the jays and severely reduced pine forest regeneration.

There isn’t room here to sketch out the whole story of jays and nutcrackers, their adaptations for seed harvesting and caching, the adaptations of trees that facilitate seed dispersal by these birds, and the sometimes complex interactions with other seed-eaters, such as mice and squirrels. For the time being, suffice it to note that the interdependence of these birds and certain trees means that if one side of the mutualism fades away, the other side declines too.

Birds at my feeders

musings on chickadees, ducks, and mallards

A gang of four Steller’s Jays regularly attends my seed-feeding stations. As soon as I go out on the deck to replenish the seed supply, they are there. One of them lets out a loud, raucous call, and then the rest come piling in, scarfing up the biggest and best seeds. After they’ve picked out the peanuts and sunflower seeds, they may take some of the little, round millet seeds, but these are usually left for the juncos.

The jays have even figured out how to raid the cylindrical feeders that I hang over my pond on a pulley system. They aren’t very graceful about it and they have to flutter their wings a lot just to stay in position, but they get enough sunflower seeds to make the level in the feeder go down rather quickly. The chickadees and nuthatches have to work around the big jays. Nevertheless, the little birds seem to do very well; there is a constant flurry of at least six chickadees whisking between the feeders and the nearby spruce trees. Whatever they reject, as they sort through the sizes and shapes of the seeds, drops down into the pond, where a gathering of mallards squabbles over each fallen seed.

Although the raucous blue rascals rather hog the show at times, they can be useful as well. One day they all worked together to harass a sharp-shinned hawk that was looking for lunch, with its eyes on all the birds congregated at the feeders. The jays swooped at it, squawking and shrieking, so all the birds knew it was there and were very wary. Eventually the still-hungry hawk gave up and left.

Jays aren’t always the ‘top dog’, however. At my feeders, when the resident squirrel approaches, on its regular rounds, the birds all move to another feeder temporarily.

Some squirrels have to work harder: A friend has observed another squirrel regularly checking seed feeders on the deck. It hasn’t quite figured out how to extract the seeds from most of them. Nevertheless, it energetically chases away the jays and other birds that come there to feed, spending a considerable amount of energy without gaining any food.

In addition to their other tricks, jays are accomplished vocal mimics, and they use this ability cleverly. They can mimic crows, red-tailed hawks, eagles, and goshawks, for example, and do it well enough to fool expert bird-watchers. A jay giving one of the predator calls generally causes other nearby birds to scatter. That potentially leaves the deceitful jay with sole possession of a food source, such as a seed feeder. A sneaky way to compete for food!

Jays also mimic marmots. Why in the world would they do that?? Marmots are not competitors for food, to be startled into fleeing. Could it be that jays simply entertain themselves, giving that active brain something more to do?

On the morning after the first hard frost, my pond had a sturdy film of ice. So the ducks were out of luck, in terms of a refuge from shooters on the wetlands. And I thought that they would all stay away from the frozen pond. But one persistent male mallard thought otherwise: he skittered and skated over the ice, snapping up spilled sunflower seeds. He had the place all to himself. A few days later, a light snow had coated the ice, and duck footprints were concentrated under the hanging feeders. Then I noticed that a female mallard had trudged up from the creek and over the ice to gobble up sunflower seeds. Relations between male and female seemed to be amicable, but occasionally the male selfishly chased the female away from the best clump of seeds.

A few days later, I glanced out my window at deck railings covered with snow and spruce branches weighted down by great clumps of snow. The pond was now frozen, so the heron that stalked the shallows a few days before was gone, and so were the opportunistic mallards. All the smaller birds were still here, including the rowdy jays.

It was very cold, so that was a nice time to remember some of those all-too-rare sunny days of summer. In the accompanying photo, two jays are enjoying a salubrious sunbath. I wonder if jays use any brain space in remembering such things when the weather turns icky!

Jays

raiders, cachers, and helpers-at-the-nest

There is a gang of four Steller’s Jays that constantly visit my seed-feeders. I assume (on no real basis whatsoever) that this Gang of Four are 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 over a dozen jays at a time.

There are over forty 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 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 that 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 two 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 one year old. However, later observations showed that 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 one, as previously thought, and others wait until age two.

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 fifty or sixty percent of their body weight (sixty to eighty 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, 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.

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Young Steller’s jays. Photo by Kerry Howard

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 that they find nests opportunistically, not as a result of a concerted search just for nests. There is always more to be learned!