Do migratory birds return to the exact same nest site?

Many do. Site fidelity is strong in species like the barn swallow and white stork, with individually ringed birds recorded returning to the same barn, chimney, or nest platform in consecutive years, sometimes for a decade or more, provided the site remains intact and undisturbed.

What's the difference between a migratory bird and a passage migrant?

A migratory bird breeds in one region covered by the atlas and winters in another, so it is present as a breeder for part of the year. A passage migrant only passes through the same region briefly while traveling between a breeding range and a wintering range that both lie elsewhere — see the passage migrants entry for details.

Bird Atlas

Migratory Birds

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Migratory birds leave their breeding range for a separate wintering range on a predictable seasonal schedule, returning to breed in the same area each spring.

Definition

A migratory bird is a species (or population within a species) that breeds in one region and spends the non-breeding season in a different, often distant, region, moving between the two on a predictable annual schedule. On a Bird Atlas species page, this shows up as a season field listing the months the bird is present to breed — for example, the barn swallow is a classic long-distance migrant, breeding across Russia and Europe in summer and wintering in sub-Saharan Africa.

Migratory status is not fixed at the species level everywhere: the same species can be migratory in one part of its range and resident in another. The common kestrel, for instance, migrates from central and northern Russia but stays put year-round in milder parts of Western and Southern Europe, since the birds there face no seasonal food shortage severe enough to force a move.

Recognizing migratory species in the field

Migratory birds tend to show a few practical field signs: they appear in large numbers over a short window (arrival in spring, departure in autumn), they often travel and stage in flocks even if solitary during the breeding season, and their numbers at a site can swing from abundant to entirely absent between seasons. The common cuckoo is a useful example — vocal and conspicuous through late spring and summer, then essentially silent and gone from Russian forests by August, having already begun its return journey to Africa well before the birds it parasitized have even finished raising its offspring.

Because migratory timing is driven by day length and food supply rather than a fixed calendar date, arrival and departure windows can shift by a week or two between years, which is why species pages describe season as an approximate range rather than exact dates.