1.1   Spring migration

The most intensive spring migration is noticed in the 2nd and 3rd 10-day periods of April. Though, this period could extend from the end of March to the end of April in different years depending on specific weather conditions. Quite frequently the observed bird migration density exceeds scale number 6. The basic weather parameters and their trends which induce mass spring migration (waves) are as follows: high and abruptly rising air temperature and cloud type (clear sky, Ci clouds).

Migration patterns and altitudes

Spring migration occurs on a broad front covering the whole of Lithuania. In the Baltic coastal areas (up to 20 KM from the coast) waterfowl are noted to predominate, while in the continental part of Lithuania - small Passerines are prevalent. The migration intensity is greater in the continental part of Lithuania. The main migration direction over Lithuania is NE-ENE. For the diurnal bird migration in the continental part of Lithuania N-NW flight direction is dominant. The Baltic Sea coast is used as a waterfowl migration passage. Night migration is more intensive than day migration and comprises 65 - 70% of all migration passages over Lithuania. The altitude of migration is up to 2500 M. 80% of all migrating birds are noticed up to 50 M at daytime and up to 1600 M at night. The most dangerous time with maximum bird migration density is: 1-3 and 6 - 7 hours after local sunset and 1,4-7 hours after local sunrise.

1.2   Summer migration

The most intensive summer bird migration occurs in July - August. Depending on weather conditions, and course in different years, migration intensity in July may be of greater or lesser volume, on the other hand higher migration may happen during August. The period - end of July and the first 10-days of August are the most hazardous when intensive migrations of Common Scoter are observed along the Baltic sea coast. Quite often the observed summer migration densities exceed scale number 6. The major factors affecting changes of summer migration periods in time are as follows: the course of summer temperatures and wind directions favourable for flights.

Migration patterns and altitudes

Summer bird migration occurs on a broad front covering the whole territory of Lithuania with great concentrations along the Baltic coastal regions as well as in the area of Curonian Lagoon and over the Baltic inland waters. The main flight direction of bird migrations over Lithuania is W-SW with predominantly S direction in the coastal regions. The intensity of diurnal migration is higher than that of nocturnal. Exceptions may take place at the end of July - the first 10-day period of August, when mass migration of Common Scoter is observed mostly during night hours. These migrations are possible over Western regions of Lithuania as well as Curonian Lagoon and the Baltic Sea but can be considered an exception. The altitudes of such migrations are: 1500 - 4000 M AGL. Velocity of bird flight is 85-120 KM/H.

For other summer bird migrations altitudes fluctuate from 10 to 150 M, seldom reaching 1000 M. The most dangerous time in the 24-hour period with maximum migration density is as follows: 1 - 4 hours after local sunrise and 1 - 2 hours before local sunset. The most dangerous time in 24-hour period at the end of July - the first 10 days of August: 1 - 8 hours after local sunset.

1.3   Autumn migration

The most intensive autumn migration occurs during the second half of September and the first half of October. Though, quite often this period is longer and varies between the end of August and the middle of October in different years depending on specific conditions and peculiarities of their course. Densities above the scale number 6 are often observed. The most important weather factors and trends, inducing mass autumn bird passage are cloud type (clear sky, Ci clouds) and favourable or crosswind wind directions. Decreasing air temperature can significantly affect the bird migration initiating waves.

Migration patterns and altitudes

Autumn bird migration occurs on a broad front covering the whole of Lithuania.

It is well expressed both at day and night by increased migration density along the Baltic coastal areas (5 – 10 KM inland). Small Passerines predominate. The amount of birds in autumn migration is considerably higher in comparison to that of spring season. The main direction over Lithuania is SW (60 - 70% of all passage) and SE-ESE (30 - 40%). The intensity of night migration is higher than day migration and comprises 75 - 85% of all passage over Lithuania per 24-hour period. The altitude of migration is up to 4500 M. 80% of all birds are registered up to 150 M at daytime and up to 2000 M at night. In Lithuania the most dangerous time in the 24-hour period when bird migration density reaches its maximum is: 1 - 4 and 6 - 8 hours after local sunset and 3 - 5 hours after local sunrise.

1.4   Numbers of birds

Over 150 million birds fly over the Western part of Lithuania and along the region of the Lithuanian Baltic Sea coast and about 50 million birds-over the continental part of Lithuania. Small Passerines predominate and the following bird species also migrate in high densities: finches, thrushes, swallows, starlings create a great hazard to aircraft. Numerous and hazardous are Anatidae: geese, ducks, swans; Corvidae: crows, jackdaws, rooks, gulls, wades,pigeons, birds of prey, there are possible different populations from several hundred to several million.

1.5   Information on densities

The ATC issues information every day when if the bird density is 5 or more.

1.6   Reporting of bird strike

Bird Strikes with Corvidae (jackdaw, rook, crow) are most frequent for aircraft of Lithuanian Civil Aviation. Strikes with pigeons, gulls, birds of prey, ducks, etc are quite common. With increasing number of flights, the number of bird strikes is also increasing.

In areas with heavy concentrations of migrating birds, the risk of a bird strike at low levels is considerably greater than elsewhere. Some birds, e.g. seabirds, may fly very low during migration. In general most migrating birds fly lower than 3000 FT (900 M). Migrating birds seldom fly higher than 10 000 FT (3000 M).

The chart ENR 5.6-3 shows birds migration routes.