Autumn marks the peak season for avian migration. This critical phase presents significant ecological and physiological challenges for migrating species. The journey to their wintering grounds is demanding, requiring substantial energy reserves and resilience. Birds, trying to reach their destination, encounter various obstacles: high mountains, vast expanses of oceans and deserts. We also contribute to the large number of birds that perish during migration – high-traffic roadways, extensive power transmission line networks, towering structures, and highly reflective glazed surfaces (windowpanes) collectively constitute significant hazards, contributing to the annual fatality of millions of migratory birds.
Hundreds of millions of birds die worldwide every year after colliding with windowpanes. It is estimated that over 100 million birds perish annually for this reason in the US alone. In Europe, the figure is about 80 million birds per year. Most of these accidents occur during the spring and autumn migrations.
Bird collisions with glass are a complex phenomenon influenced by several interrelated factors. The primary causes are the inherent properties of glass—its transparency and reflectivity. Most birds do not perceive glass as an obstacle but rather as open space: in window reflections, they see trees, shrubs, and the sky. Birds interpret these reflections as a continuation of the surrounding environment or as a safe refuge, rather than an impenetrable barrier. As a result, they do not slow down when approaching buildings and often fly directly into the glass.
This issue is also highly relevant in Lithuania—recent days have seen a significant number of bird fatalities reported across the country. Experts emphasize that these incidents coincide with the peak of the autumn migration period, when millions of birds pass through Lithuania on their journey from northern regions to wintering grounds further south. The intensity of this migration is confirmed by data from the Ventė Cape Ornithological Station, where as many as 44,000 birds were ringed in the month of September alone.
A particularly high number of bird fatalities has been recorded in the coastal region. This area forms an important part of the White and Baltic Sea migratory flyway, used each year by large numbers of birds of various species. During the autumn migration, up to one million birds may pass through the Klaipėda area in a single day.
To prevent bird fatalities caused by collisions with building glass, many European countries use patterned or opaque glass. During the renovation of its Ventė Cape branch, the Tadas Ivanauskas Zoological Museum in Kaunas replaced all windows with special glass marked with dotted patterns. Such windows are clearly visible to birds, preventing them from flying into the glass.
To effectively protect birds, more comprehensive research on this phenomenon and corresponding evidence-based regulations are essential. Scientific data would allow for a more accurate assessment of the scale of collisions and help identify the most effective mitigation measures. Nevertheless, each of us can contribute to bird conservation. One of the simplest and most accessible measures is applying silhouettes of birds of prey or other bird-protection markings to windows. Such visible objects help birds recognize glass surfaces as obstacles, thereby reducing the risk of collisions and fatalities.
