It was just a bridge, not even a special bridge. The Heiwa Bridge spans the eastern end of Lake Tofutsu in northeastern Hokkaido. To the north there is a narrow neck of wooded land and then the Okhotsk Sea. To the south lies more woodland, then great expanses of farmland. It was just a bridge, but suddenly I discovered it was also something of a flyway!

One jay from among more than 500 surprisingly sighted en route from the cold, moutainous north to warmer regions of Hokkaido one day this fall.

Flyways are the routes followed by migratory birds in spring and autumn. Each year, as the autumn migration season approaches, I begin to get itchy feet. Island migration watch-points are my favorites -- Hegurajima (Sea of Japan, Ishikawa Prefecture), Teurijima (Sea of Japan, western Hokkaido), Fair Isle (Atlantic, off northern Scotland), the Scilly Isles (Atlantic, off southwestern England). But capes, headlands and even certain mountains have their appeal, as anyone will know who has been to Irago Misaki (Aichi Prefecture), Cape May (New Jersey), Hawk Mountain (Pennsylvania) or to the mountains behind Eilat in southern Israel. Just why are migration seasons so exciting?

Part of the pleasure of living in the northern temperate zone is observing how different creatures adapt as the seasons unfurl. Some hibernate, while others avoid winter by moving. That means that, during spring and autumn, migratory birds may appear in the most unusual places. In Japan, flycatchers and warblers, otherwise rarely seen in the cities, suddenly and unexpectedly appear in parks; shorebirds from Siberia or Southeast Asia suddenly appear at coastal wetlands; ocean-roaming shearwaters and albatrosses may be blown close to shore, or even onshore during autumn gales or typhoons. Autumn in particular is a season of surprises.

The most exciting aspect of migration is that there is no way of knowing what is coming next. Of course, visiting a renowned watch-point means there is always the chance of spotting a rarity, although common species are exciting too -- especially in large numbers.

Earlier this month, I was feeling decidedly jealous of folks at Irago and on Hegurajima, but I had to make do instead with three days along the Okhotsk Sea coast, checking out sites for research later in the autumn.

One of my favorite places in that part of the country is that shallow coastal lagoon known as Lake Tofutsu. On my most recent visit in early October, it was packed out with several thousand wigeon, as well as smaller numbers of mallard, shoveler, pintail, scaup and pochard. The first of the swans had arrived, too; there was a pair of whoopers and a family of Bewick's swans. There was also a sizable gathering of bean geese roosting there at night. All were normal fare for the time of year.

Though I began my three-day trip feeling envious of migration-watchers around Honshu, by the end of my journey along the Okhotsk Sea coast west and east of Abashiri, I had not only seen a wide range of waterfowl, but also my own set of rarities. At Lake Komuke I'd spotted a Lapland bunting, at Lake Notoro an oystercatcher, and at Lake Tofutsu a long-billed dowitcher.

I made my camp that night in distinctly higher spirits -- perhaps being marooned up in Hokkaido in autumn wasn't so bad after all! The next day dawned reasonably fair, so I indulged myself in my secondary and tertiary passions: I hiked up Shari-dake amid glorious autumn colors and followed that with a long soak in the local onsen. Could life get better?

The following morning I woke to a crystal-clear dawn and the sound of bean geese honking as they flew over from their roost to their feeding grounds. The weather was 10 times better than the day before, and to the east Shari-dake was starkly clear. What should I do? Where should I go? I needn't have worried -- Mother Nature took over and made her own plans for me.

Something tremendously exciting was going on around me. My camp was beside the road just north of the 70-meter-long Heiwa Bridge. The narrow neck of land to the north and the bridge together form a kind of funnel separating Lake Tofutsu from another smaller lake just to the east.

As I prepared breakfast, I noticed a surprising number of small birds calling overhead and small flocks of jays clearly on the move, and all heading the same way -- south over the bridge. I was surrounded by migrants!

If you are familiar with jays, you will know of them as somewhat secretive forest birds. They are rather weak fliers, lumbering members of the crow family that gather nuts and acorns, and flop about in the forest in a rather ungainly manner while occasionally making sharp rasping sounds in alarm. Though jays seem to be poor fliers, each September and October I have been very aware that I suddenly see far more of them about than at any other time of year.

Whenever I travel to the mountains at this time of year, I seem to see small parties of them undulating their way weakly over the forest tops. I have glimpsed them flying alongside highways and flapping across deep valleys, and I've even seen them from trains. But there on the Heiwa Bridge, they were coming straight at me. That neck of land is aligned north-south, and it was over this that the jays were coming singly, in small parties, and even in large flocks en route from the mountainous Shiretoko Peninsula to the warmer winter climes of inland lowland Hokkaido.

It seemed as if they were gathering to the north in a small clump of trees, then when they reached some critical mass they would set out southward, passing no more than 20 or 30 meters over me and disappearing southward into the woodland and farmland.

I was immediately entranced by the amount of bird movement and gave myself an hour to watch. At the end of the first hour, though, I was so hooked that I stayed another, then another. I finally dragged myself away after four solid hours of counting birds across that bridge. How I wish I could have collected tolls! In those four early morning hours, without moving from my spot, I had encountered no fewer than 25 species of migrants -- and that's not counting the waterfowl on the lake.

The most unusual migrant was an early Steller's eagle, which was actually the only bird not flying south. A hen harrier, a sparrowhawk and a kestrel made for some excitement among the other birds, but it was the accumulating numbers that excited me.

Buntings, pipits, wagtails, oriental greenfinches and hawfinches all passed over rather high, and I no doubt missed many of them, but closer above my head came the brown-eared bulbuls -- some 28 of them in the four hours.

Flying even lower came five great-spotted woodpeckers, three Japanese pygmy woodpeckers and nine nuthatches, each of them undulating along separately and southbound away from the rigors of winter farther north. Lower still were flocks of tits, some of them even below head-height and others almost landing on me as they hurtled by.

It is one thing to encounter a mixed flock of such birds foraging in a leafless forest in winter, but here they were all urgently fleeing past me southward: 102 great tits, 131 marsh tits and an amazing 197 coal tits. It was those jays, though, that provided the biggest surprise.

I have long been aware of their tendency to be on the move in autumn, but this was my first time counting them. They just kept on coming, more and more groups flopping past until I had totaled 512 individuals by 10 o'clock. I forced myself to stop then, to pack up and set off back to Sapporo. Just then, however, another flock of 37 jays flew past, as if to confirm this was no flash in the pan, and not just a movement of early starters.

After four hours of really enjoyable watching, I had totaled 1,111 migrants of 25 species -- probably the most birds I have ever counted on migration. And I wasn't even at a recognized migration watch-point! My faith in the capacity of autumn to fill me with surprises had been richly rewarded, and I learned that I needn't, after all, have been envious of more famous watch-points; I had found my very own!