Much remains to be explained about these familiar birds
When a species is as common as the blue jay, we tend to take it for granted. We are often dulled into thinking that there’s little new to be discovered about its behaviour. Well, think again. From their aggressive mobbing behaviour and seed caching, to their enigmatic migrations and mimicking of other species, there is much that remains a mystery. We even have to be wary of our own senses. A jay’s feathers, for instance, aren’t really blue. The colour pigment they contain is actually brown. The blue we see is caused by the scattering of light by special cells in the feather barbs. The feathers appear almost black when backlit.
A big part of the blue jay’s success as a species comes down to being a generalist. They will eat everything from seeds and nuts to insects and carrion. Even the eggs and nestlings of other species are sometimes on the menu. When jays visit feeders, they prefer peanuts, suet and sunflowers offered up on a tray or hopper feeder. Just this week, I watched as one jay gobbled up at lest 20 sunflower seeds, before flying off presumably to cache them.
Jays have a pouch in the throat and upper esophagus in which they transport food – as many as three acorns at a time, for example. They then store the food in caches – often in the ground – to be eaten at a later date when the pickings are scarce. One study showed that a single blue jay can cache up to 5,000 acorns over the course of an autumn. Some of the food, of course, is never eaten, so acorns can end up germinating and producing new trees. It is believed that jays are responsible for the spreading of oaks after the glaciers retreated. However, the extent of caching appears to differ widely among individual jays.
Because this year’s crop of acorns, beechnuts, hickory nuts and beaked hazelnuts is quite good, it appears that large numbers of jays will remain in Kawarthas this fall and winter. I am already seeing a lot more than this time last year. But, as we’ll see later, the link between food availability and migration is far from clear. Although much of their winter diet consists of acorns – at least in parts of their range – jays cannot survive on these nuts alone. Some of the literature even states that jays don’t really care for the acorns of red and white oaks, which are the two main species here in the Kawarthas. Go figure.
It was once thought that the eggs and nestlings of other species made up a big part of their diet, too. This habit even attracted the attention of John James Audubon, who wrote, “It robs every nest it can find, sucks the eggs like a crow, or tears to pieces and devours the young birds.” The actual extent of nest predation, however, is unclear. Recent studies show that eggs and nestlings make up a negligible part of a jay’s diet.
In one famous study on the palatability of monarch butterflies, captive blue jays were fed monarchs. As caterpillars, the monarchs had been raised on milkweed leaves, which is the only plant the larvae will eat. Ingesting the butterflies caused the jays to vomit, and they refused to ever dine on them again. It is now a well-known fact that monarchs are unpalatable to birds.
We have blue jays in the Kawarthas every fall and winter, but the number varies significantly from one year to the next. Fall migration is most noticeable in mid- to late September, although it does continue until the end of October. Jays return to the Kawarthas in May, when migrants arrive back to join their brethren who never left.
The best place to observe fall migration is along shorelines of Lake Ontario and Lake Erie, where thousands can be seen daily. The birds fly in a loose, string-like flocks ranging in size from about six to over a hundred jays. They travel during the day- especially in the morning – and are usually silent. In the autumn of 2007, hawk watchers at Holiday Beach, south of Windsor, counted 50,000 jays streaming past in a single day. That being said, it is believed that no more than 20 percent of the population migrates, even in northern parts of the blue jay’s range.
No one has figured out why an individual jay or jay family migrates when or if they do. Some individuals migrate south one year, stay north in their nesting area the following winter, and then migrate again when the next fall rolls around. Individuals that depart an area in autumn may be replaced by those migrating from farther north. It was once thought that young jays migrate more than adults, but recent analyses of banded jays show no significant age difference between migrant and resident birds. Migration may indeed be related to the availability of wild food, but this is not yet certain.
“Along the line of smoky hills / The crimson forest stands / And all the day the blue jay calls / Throughout the autumn lands.” These words by the Canadian poet William Wilfred Campbell are as true today as they were in 1889. The loud and brash calls of jays are maybe the most typical bird sound of early fall. Blue jays are well known for their large variety of vocalizations, the most familiar of which is a shrill, descending “jaaay” scream. They also make a whistled “toolili” sound, which is often referred to as the “rusty pump” call, since it resembles the sound a hand-operated water pump. Quiet, clicking rattles are also common. Unlike other songbirds, blue jays don’t sing as such. This may be because they are not territorial and don’t appear to defend a discrete space the way that robins do, for instance.
Jays are also mimics and do an amazing rendition of red-shouldered hawk calls. Why they do so is unclear. It may signal to other jays that a hawk is present, or it may be a feeding strategy. Upon hearing the jay’s uncanny hawk imitation, some birds immediately fly away. The jay then eats the food left behind or raids its nest. Like migration, this is an area where much more research is needed.
Jays also use body language to communicate. Holding the crest down low, for example, indicates a lower aggression level. The opposite is also true. Watch the next time you see a blue jay squawking: the crest is usually erect.
Jays, like crows, blackbirds and chickadees, often take part in mobbing behaviour, which refers to a group of birds fluttering and calling loudly around a perched hawk, owl, cat or other predator. The purpose of this behaviour is still debated, but it seems to be done in an effort to hound the intruder until it decides to move along. In the case of a hawk, it is not clear why the pestered raptor doesn’t simply turn on its tormentors and grab one or two for an easy meal.
Blue jay populations have remained constant for years, despite some mortality in recent decades from West Nile Virus. The 2000-2005 Ontario Breeding Bird Atlas shows a small northward extension of range, possibility because of more people feeding birds. Jays are most abundant in the southern shield region, which includes The Land Between. You can also find large numbers of jays in older urban and suburban areas of large cities throughout southern Ontario. Like many generalist species, jays adapt easily to changes in the landscape, and their populations may actually increase with climate change.
Male vs. female
People have often wondered how birds like blue jays and Canada geese recognize the opposite sex. In both species, the male and female appear identical to human eyes. The only apparent difference between individual jays – but not the sexes – is the size and shape of the black bridle or necklace across the nape, face and throat. This may help jays recognize different individuals.
Research now is revealing that birds have much better colour discrimination than humans. They see an entire range of colours that we cannot perceive or even imagine. This includes colour in the ultraviolet range. This means that birds may actually be seeing distinct differences in plumage colour. They may see colours that are unimaginable to us such as a blend of ultraviolet and yellow. Colour, of course, is a construct of the brain.
In one study, a stuffed male and female yellow-breasted chat, a type of warbler, were placed in a cage with a wild, living male chat. Since it was the breeding season, the wild male attacked the stuffed male in an effort to chase it from the cage. However, it displayed mating behaviour in front of the female. There is an important lesson here. As humans, we must learn to be much more modest about how we perceive the world. We have evolved in a limited perception bubble. We have significant sensory shortcomings and are by no means the pinnacle of evolution. In evolution, course, there is no pinnacle – just differences. As Joe Smith wrote recently in Cool, Green Science, “We must accept that as beautiful as birds appear to us, we will never be able to behold their true colors. We are left only to revel in the known unknowns and wonder about the ‘unknown unknowns’ yet to be discovered in the invisible world around us.”