ENR 5.6 BIRD MIGRATION AND AREAS WITH SENSITIVE FAUNA

1 Bird Migration

Bird migration occurs during the whole year but culminates in the period April-May (spring migration), July-August (summer migration) and September-November (autumn migration). The factors that affect migration most are time, weather (visibility, air temperature, wind direction and speed, precipitation) and Moon phase. Height of the migration is greater in case of tailwind than in case of headwind.
1.1 Spring Migration
Spring migration begins in mid-March, ends in mid-June and culminates in the period April-May. Peak numbers for most species occur in this period with high densities very frequently. The most important factors inducing heavy migration are a rise in temperature, tail- and crosswinds.
1.1.1 Migration Patterns and Heights
During the night, migration is generally on a broad front covering the whole country and its surrounding waters, with general direction from SW to NE. General range of migration's directions’ variability is 90°, reaching from N to E. Generally night migration and migration over the continental part is higher than migration by day and along coastlines. During the night and over the continent the average height is APRX 500-1500 m; during the day and over the coastline, APRX 50-500 m.
1.2 Summer Migration
Summer migration begins in the beginning of July, ends in the beginning of September and culminates in the period from mid-July to mid-August. Migration takes place mostly in the early morning hours and late in the evenings, especially around midnight.
1.2.1 Migration Patterns and Heights
Prevailing direction of migration is SW, but dependent on different areas that varies from NW to S, so the general range of variability of migration's directions’ is 135°. Daily migration takes place mostly above the sea, concentrating near the coastline. Migration during night takes place above land as well as sea, concentrating roughly on the lines Kunda-Virtsu and Narva-Pärnu. Prevailing heights of migration are 100-2000 m above land and up to 300 m above sea.
1.3 Autumn Migration
Autumn migration begins in the end of August and ends in the beginning of December, culminating in the period from mid-September to mid-November. Peak numbers for most species occur in October with high densities frequently. The most important factor inducing heavy migration is a fall in temperature. High densities are also correlated with northerly winds, light winds, little cloud cover and high pressure. Migration takes place mostly during 3-4 early morning hours, starting roughly half an hour prior to sunrise. Another intense period of migration is around midnight.
1.3.1 Migration Patterns and Heights
During the day and night, migration is on a broad front covering the whole country and its surrounding waters, with general direction from NE to SW. General range of migration's directions’ is 180°, varying from NW to SE. Prevailing height of migration during night is 500-1500 m (max 3000 m) and during daytime 100-1000 m (max 3500 m). Migration above sea takes place mostly at heights up to 300 m.
1.4 Number of Birds
A lot of birds pass over Estonia and its surrounding waters during spring and autumn. Waterfowls are dominating, and several species occur in great densities and are very hazardous to aircraft, e.g gulls, geese, sea ducks and swans. Therefore the most dangerous areas are located in western and northern parts of Estonia (especially coastal regions). Crows, starlings, swifts and birds of prey are also hazardous and very numerous.
1.5 Information on Densities
During spring migration some 40 million birds fly over Estonia, during summer migration this number is about one million.
1.6 Caution Note
It should be avoided to fly lower than 300 m (preferably 500 m) along the coastline and rivers as well as over islands and sea islets during the migration periods and bird nesting period (APR-JUL).
1.7 Reporting of Bird Strike
To achieve more comprehensive statistics of bird strikes, the Civil Aviation Administration is collecting information. All pilots on flights within Tallinn FIR are therefore requested to report to the Civil Aviation Administration all cases of bird strike or incidents where a risk of bird strike has been present.
1.7.1 Reporting

To facilitate the reporting of incidents, a Bird Strike Reporting Form has been produced and may be obtained at airport offices at public aerodromes or from the Civil Aviation Administration. Any supplementary information on the circumstances under which the incident took place should also be added.

The index chart ENR BIRD shows the main bird migration routes, with an indication of the migration periods and heights above ground level.

The index chart ENR OTHER shows the bird concentration for the period MAR-MAY.

2 Areas With Sensitive Fauna

2.1 Many species of birds and animals are sensitive to noise from aircraft and overflying their breeding and resting places may be critical. In accordance with the regulations of Ministry of Environment overflying of such areas at heights below 1500 ft shall be avoided.
2.2 The areas are shown on the index chart ENR OTHER.