[Genesis 1:22]
 

And God blessed them, saying, “Be fruitful and multiply, and fill the waters in the seas, and let birds multiply on the earth.” [NKJV]
 

And God blessed them, saying, Be fruitful, and multiply, and fill the waters in the seas, and let fowl multiply in the earth. [KJV]

It's the first appearance of the word, "Blessed" in Genesis, and it involved God blessing the living creatures of the marine world. When God blessed them, He spoke a Word of God that empowered them to be fruitful and to multiply until they fill their habitations.
 

"Blessed them" was used rather than "Numbered them." Both are related, except that numbering them would mean summing (counting) their numbers while blessing them meant multiplying their numbers. These living creatures became blessed by God with procreation or reproduction of themselves, to increase and multiply themselves above the numbers at which the waters brought them at first. They were blessed to buildup and upgrade their numbers and their multiplication among themselves, and now the book of their population statistics must be updated daily.
 

Also the blessing of God upon them turned their assignment into blessings to them. The more they fulfilled their purpose (assignments) to their habitations, the more they were blessed and enlarged to do more than they did previously. But basically even their blessing came to serve their purpose.
 

God's blessing however gave a different habitation to the birds, and made the earth their habitation. Blessing can be locational and regional to some particular places or realms: and in such cases, one just have to access the blessings through abiding in such places or realms where the blessings are kept for such person. Even so, the birds had habitation on earth in agreement with their blessing and they were blessed to multiply on the earth and to fly above the earth. They may both move with their legs and with their wings. They may walk, run and fly, and some of them may float on the waters or may swim briefly in the waters. Basically, the blessing of God on them increase the abilities and capacities in their bodies. The more blessed of God you are, the more abilities and capabilities your body will have to be and do things by the blessings, which some other bodies cannot do.