When it comes to migration, the blue jay, among our most familiar and recognizable birds, plays by its own rules. By and large, the species is a permanent resident of most of its vast geographic range; individuals may move around a bit in winter for better access to food, but they don’t travel far. However, most years at least, a small percentage of blue jays migrate south, and some years (years of poor acorn production, goes one theory), the majority of jays pull up stakes and head south.
Blue jay migration can be either a striking phenomenon or a subtle one. Sometimes large aggregations of jays head south along river valleys or along the coast; locations like Cape May, N.J., where geography funnels bird migration down into the Garden State’s skinny southern apex, can see huge concentrations of migrant jays. I’ve seen totals in the thousands moving during the course of single days along the coast.
But the movement of these birds can also be so discreet as to be easily overlooked. For example, as I was traveling out to Western Massachusetts a couple of weeks ago, it only gradually dawned on me that a steady supply of jays was moving south across the highway in groups or three or four birds, even as single individuals. One such encounter barely even registers. But in the course of traversing the state, I’m sure I saw hundreds of jays, virtually all of them chugging industriously southward. Assuming the movement continued before and after I passed a given location, many thousands of jays headed south through Massachusetts that day.
Whether singly or en masse, blue jays tend to migrate by day and at low altitude, often just above treetop level, flying at a relaxed but businesslike pace. Flocks, when they exist, are loose and unstructured; individual birds sometimes drop out, perhaps to feed, then either stay behind or dash to catch up with the group. All in all, jay migration suggests to me that individual birds make up their own minds, and that migration is more a rational process (by bird standards, I mean) than any sort of instinctive mass movement. Individuals, perhaps with the aid of some sort of birdy consultation with their friends and relatives, make their own decisions about whether, when, and how far to migrate.
My impression so far is that 2019 will prove to be one of those years featuring a heavy migration of blue jays. For weeks, large flocks of jays were unmissable around the Gay Head Cliffs, 200 to 300 birds circling around the area and apparently contemplating (but never, as far I could observe, quite undertaking) flight westward across Vineyard Sound. Most likely these birds were of local origin, though it’s possible that some or all were transients from farther north. If local, though, the Gay Head flock surely represented a significant percentage of the Vineyard population of this species. I gather they’ve moved on, after a period of indecision, perhaps taking advantage of northeast winds in recent weeks.
Blue jays aren’t absent now from the Vineyard, but my impression over the past couple of weeks is that numbers have declined appreciably from earlier in the year. Again, though, it’s hard to say whether some of our birds have remained, or whether the Island jay population has been partly replaced by birds from the north. It’ll be interesting to see results from this winter’s Christmas Bird Count (CBC) for this species — will jays be scarce?
The connection I mentioned earlier between heavy jay migration and acorn production makes sense. Blue jay natural history largely centers around oak trees, and acorns are a prominent part of this bird’s diet. Rich in oaks, the Vineyard is no doubt a congenial place for blue jays. CBC results typically include blue jay numbers in the low- to mid-hundreds, but those figures may reflect a winter population depleted by migration, as well as the difficulty of accurately counting a species thinly dispersed across large tracts of oak woodland.
If acorns are a favored food for this bird, they’re far from the only thing jays eat. Studies suggest that insects make up a large percentage of a jay’s diet during the warmer months, and at all times of the year, they dabble widely in seeds (including sunflower seeds, taken either at feeding stations or from ornamental sunflowers). Blue jays do raid nests of smaller birds, taking eggs or even nestlings, and they have been observed killing and eating prey up to the size of small rodents. But most sources suggest that such predatory habits represent a fairly small percentage of a blue jay’s foraging effort.
Raucous, sometimes aggressive, and surprisingly beautiful if you take a careful look, the blue jay may be a familiar bird. But this is an intelligent and resourceful species: Whatever you may know about the blue jay is true only some of the time, and their mysterious ways make them one of my favorite birds.
