Bird watchers said despite ample sources of food and numerous live hatchings, many young birds died of cold and exposure, Polskie Radio reported Thursday.
In one traditionally popular habitat of white storks in southwestern Poland, 26 pairs had nested this year but only six pairs managed to raise a total of nine hatchlings, ornithologists said.
Violent rains and sudden spells of cold weather in June may have also brought on fungal infections, a common problem in damp weather, they said.
Storks in western Poland were hardest hit, and conservationists said they were hoping storks raised in central and eastern Poland -- which escaped the worst of the spring weather -- would help rebuild the decimated populations in the western part of the country within three to four years.
Bird watchers said it has been the worst year from storks in Poland since 1997, when much of the country was hit by flooding.