More than 30 species of waterbirds pass through the waters of Latvia's territorial and exclusive economic zone during the annual cycle. Most bird species are observed during migration or wintering, but some marine waters of the species are used as a place for changing feathers and driving babies. During wintering and travelling, birds tend to stay relatively close to the coast – up to 20 m isobath, where the best feeding conditions are present. Wintering water birds are found in the sea and inland waters. Birds wintering at sea shall deliberately arrive, migrating from nesting or changing feathers which are frozen in winter. The most typical wintering waterbirds in the sea are long-tailed, big-tailed, black-duck, dark duck, cricketer, silverbirds, kayaks, and many others. Several of these species, such as long-tailed ducks, can form huge flocks, up to several tens of thousands of individuals.

The quantities of wintering birds are listed each winter, organized as soon as possible, with surveys of inland waters and the whole sea coast. The number of seven species (brown-necked and black-necked diver, long-tailed duck, black duck, dark duck, small chore and black crave) is of international importance and therefore five of the seven protected marine areas established in the territorial waters of Latvia are intended for the protection of birds.

In 2016, the first wintering waterbird avio-count took place in Latvia's history, covering all the marine Proper owned by Latvia – territorial waters and the waters of the exclusive economic zone. Avio-counts of wintering waterbirds, as a monitoring method, have continued regularly since 2016. Under LIFE REEF, all existing monitoring data will be evaluated, additional records of feathered and migratory waterbirds will be carried out. If it is scientifically demonstrated that large populations of waterbirds, such as long-tailed ducks, are present in the project's exploration areas, LIFE REEF will make proposals for the development of new Natura2000 sites in the exclusive waters of the economic area, not only for the protection of habitats but also for waterfowl.

Wintering waterbirds may move closer or further during winter between different feeding areas, particularly when a layer of ice occurs. Birds at wintering sites, open waters, stay throughout the wintering season until they go into spring migration to nesting sites.

The main condition during the wintering of birds is the feed available at the depth of their feeding strategy and the surface of unfrozen water.

The “feeding strategy” of waterfowl is one of the ways in which birds are classified:

Benthic birds (benthic organisms live close to the base of the water body, in a pristine layer) are deep diving birds that feed on mollusks, such as the dark duck and long-tailed duck.

Pelagic birds are divers feeding in free water above the bed, such as the big gaura.

Herbivores are birds that do not dive but live on water plants reached in the shallows (outside the wintering season also from terrestrial plants), such as swans. These birds tend to move between feeding and staying places every day, because feeding places close to the shore can be threatened by predators at night.

Surface-feeding birds feed with fish visible close to the surface of the water, such as silverbird.