Talking to Sunday's "Hommik Anuga" show, the expert, Tarvo Valker, said the arrival of certain species is known to be a clear sign that spring has sprung, so far as nature goes. "The skylark and the northern lapwing are [two of] those; when you hear the skylark's song and see that the lapwing has arrived in the fields, it really feels like spring for the birds has started," he said.

The early arrivals are perhaps taking a risk, insofar as birds can take risks, however, as the weather can be highly changeable. A return to winter can even prove fatal to some species, though it is not unheard of in such cases for birds to take off and head back south for a bit to wait out the cold spell.

As to why summer visitors can arrive as early as February or March, Valker said: "There is a very specific reason for this rush: they want to secure the best possible nesting sites, and there is competition for those sites."

Bird migration in Estonia has been the subject of academic study for about a century now, and Valker noted these longer-term data sets have proven extremely valuable. Extended observations have shown that several early-spring migratory birds now arrive in Estonia considerably earlier, meaning several weeks earlier, than before — for example the greylag goose, as well as the lapwing and skylark.

Whereas these species used to arrive around mid- to late March, they now often appear as early as mid-February.

This year notwithstanding, the milder winters are the main factor here, Valker said. "So long as there isn't deep snow or severe cold, early-spring birds can arrive very early. For example, last year we had a very mild winter, and the first common cranes and greylag geese were already here in the first week of February. Last year, the first chimney swift arrived on March 9. Imagine going outside on a Monday and a chimney swift flies over your head. Very, very big changes."

Over time, the makeup of bird species ordinarily found in Estonia has changed too, he said. Some species have disappeared, while others have arrived. The red-backed shrike, for instance, has disappeared from Estonia, while the little egret and the western marsh harrier are among the newer arrivals.

Valker also noted that there are more bird species whose populations are declining than those that are doing well. Species that depend on old forests are particularly at risk, but even then populations of many species found in cultivated agricultural landscapes have fallen too. "For example, the population of the corncrake has dropped dramatically. The reason for that is that agriculture is becoming increasingly intensive, and there are fewer meadows and small field patches left."

Different family models among bird species

Spring also marks the start of the bird breeding season. In the bird world, females play a key role in selecting a mate. "They actually choose the males; it's not the male choosing the female," the ornithologist noted. Males try to impress females through song, courtship displays, or bright plumage.

According to Valker, different bird species exhibit different models of family care: Some species are cared for by both parents, while in others only the female cares for the young. In some cases, it is solely the male that ends up raising the chicks. "The female only lays the eggs; the male incubates and takes care of the young alone," he added.

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