1. BIRD MIGRATION

1.1 Bird migration occurs during spring, summer and autumn periods. Intensive movement of birds wintering on the Baltic Sea, Riga Bay is typical to the Latvian sea coast. The greatest degree of activity is observed during the following periods: end of MAR- whole of APR - beginning of MAY (spring migration) and the end of - whole of OCT (autumn migration). Well-expressed summer bird migration is observed in JUL - AUG and winter movement in DEC - JAN. The latter is more characteristic of the Western and coastal regions of Latvia. Weather conditions may affect bird migration or (movements) during different periods of the year.

Surveillance radar measures bird density using the scale zero to eight as follows:

0 = No birds observed

8 = Maximum bird densities.

In Latvia, especially in its Western parts, the bird density during seasonal migrations often reaches the scale of 6 - 8.

1.2 Spring migration

The most intensive spring migration is noticed in the second and third 10-day period of APR. Nevertheless, these periods can extend from the end of MAR to the end of APR in different years depending on specific weather conditions. Quite frequently, the observed bird migration density exceeds the scale number 6. The basic weather parameters and their trends that induce mass spring migration (waves) are as follows: high and abruptly rising air temperature and cloud type (clear sky, Ci clouds).

1.2.1 Migration patterns and altitudes

Spring migration occurs on a broad front, covering the whole of Latvia. In the Baltic coastal areas (up to 20 km from the coast) waterfowls are noted to predominate, while in the continental part of Latvia - small passerines are prevalent. The migration intensity is greater in the continental part of Latvia. The main migration direction over Latvia is SN-SNE. For the diurnal bird migration in the continental part of Latvia, a WE 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 passage over Latvia. The altitude of migration is up to 2500 m. 80% of all migrating birds are sighted 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 SS and 1, 4 - 7 hours after local SR.

1.3 Summer migration

The most intensive summer bird migration occurs in JUL - AUG. Depending on the weather conditions, and course in a given year, migration intensity in JUL may be of greater or lesser volume which causes higher migration during AUG. The period from the end of JUL and the first 10-days of AUG are most hazardous, when strong migrations of common scoters are observed along the Baltic sea coast. Quite often, the observed summer migration densities exceed the scale number 6. The major factors effecting changes in the summer migration periods over time are as follows: the course of summer temperatures and wind directions favourable for flight.

1.3.1 Migration patterns and altitudes

Summer bird migration occurs on a broad front, covering the whole territory of Latvia, with great concentrations along the Baltic coastal regions and over the Baltic inland waters. The main flight direction of bird migrations over Latvia is W-SW, with a predominantly S direction in the coastal regions. The intensity of daytime migration is higher than that of nighttime migration. At the end of JUL and during the first 10-day period of AUG, mass migration of common scoters is observed mostly during nighttime hours. These migrations are possible over western regions of Latvia and the Baltic sea but can be considered an exception. The altitudes of such migration are: 1500 - 4000 m AGL. The velocity of bird flights is 85 - 120 km/h.

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

1.4 Autumn migration

The most intensive autumn migration occurs during the second half of SEP and the first half of OCT. Though, quite often, this period is longer and can vary between the end of AUG and the middle of OCT 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 following of crosswind wind directions. Decreasing air temperature can affect bird migration, initiating waves of migratory fowl.

1.4.1 Migration patterns and altitudes

Autumn bird migration occurs on a broad front covering the whole of Latvia. It is recognised 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 during the autumn migration is much higher in comparison to that of the spring season. The main direction over Latvia is NS (60 - 70% of all passages) and NSW (30 - 40%). The intensity of night migration is higher than that of day migration and comprises 75 - 85% of all passages over Latvia 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 nighttime. The most dangerous time in a 24-hour period in Latvia when bird migration density reaches its maximum, is: 1 - 4 and 6 - 8 hours after local SS and 3 - 5 hours after local SR.

1.5 Number of birds

More than 150 million birds pass over the western part of Latvia and along the region of the Latvian Baltic Sea coast and about 50 million birds pass over the continental part of Latvia. Small passerines predominate and the following bird species also migrate in high densities: finches, thrushes, swallows, starlings, and create a great hazard to aircraft. Numerous and hazardous are Anatidae: geese, ducks, swans; Corvidae: crows, jackdaws, rooks, gulls, waders, pigeons, birds of prey, populations from several hundred to several million are possible.

1.6 Information on densities

NIL

1.7 Caution note

When an intensity of 5 or more is reported, it is recommended to fly above 500 m AGL at daytime and 2000 m AGL at nighttime.

1.8 Reporting of bird strike

1.8.1 General

Bird strikes with Corvidae (jackdaw, rook, crow) are most frequent in Latvian civil aviation. Strikes are quite common with pigeons, gulls, birds of prey, ducks, etc. With increasing flights, the number of bird strikes is also increasing. We forecast a 5-fold increase in bird strikes in Latvia when such types of aircraft as Boeing begins to be used.

To achieve more comprehensive statistics on bird strikes, the ATS wants to collect information from the civil aviation community. All pilots on flights within the Riga FIR are therefore requested to report all cases of bird strikes or incidents where a risk of a bird strike has been present. Report these incidents to the ATS of Latvia.

1.8.2 Risk of bird strike

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

1.8.3 Reporting

For use, when reporting, a Bird Strike Reporting Form has been produced. This form may be obtained at airport offices at public aerodromes or from the ATS.

In connection with incidents on or near an aerodrome, pilots are requested to arrange for the bird, or as much of the remnants, as possible to be collected and sent to:

Post:

Head of Laboratory of Ornithology

Institute of Biology of the University of Latvia

Ojāra Vācieša iela 4

Rīga, LV-1004, Latvija

supplemented by information on the circumstances in which the incident took place.

Figure 1 shows the main migration routes.

2. AREAS WITH SENSITIVE FAUNA

2.1 Many species of birds and mammals are sensitive to noise from aircraft and overflying their breeding and resting places, even at a low rate, may be critical.

According to the Regulations for civil aviation of Latvia, overflying of such areas at heights below 1000 FT shall be avoided.

Figure 1. BIRD MIGRATION ROUTES