Every year, a census of owls—nocturnal birds of prey inhabiting the Holosiivskyi Forest—is conducted in the Holosiivskyi National Nature Park in Kyiv. As part of educational events at the ‘Zelenyi Val’ youth eco-centre, researchers set out on evening walks and identify the birds primarily by their calls. This approach allows researchers to determine the number of individuals, their locations, and track population changes over the years.
Such observations help to better understand the state of the natural ecosystem. To maintain its balance, it is important to know the numbers and distribution of different species, as well as their interrelationships. For example, by understanding the size and density of the grey owl population, researchers can make assumptions about the numbers of small rodents — the main prey of these birds — and generally assess the availability of food in the forest. In conservation work, such information helps to plan measures for the preservation of biodiversity.
We have been carrying out these surveys for three years now. And why now, of all times? In our case, it was postponed until March because we had a very cold winter, particularly in February, and the owls weren’t hooting as much.
Serhiy Khara — an environmentalist and biodiversity campaigner at Greenpeace Ukraine, and head of the environmental education department at the Holosiivskyi National Nature Park.
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How owls count
– We will make use of this state of mind and identify the owls by their calls: what species they are, their sex, and where they are located. The data collected will be plotted on graphs and a map – this will allow us to track changes in the population’s distribution across the study area.
One of these survey routes passed through the Holosiivskyi Forest. The participants stopped at pre-determined points, where they carried out acoustic surveys to check for the presence of birds.
– Every year we follow the same routes; sometimes we add a new route, and where possible we repeat that new route year after year to cover as much territory as possible and understand the distribution of the owl population throughout the forest.
What kinds of owls live in Holosiivskyi Forest?
According to records and ‘nature chronicles’, three species of owl have been recorded within the park: the tawny owl, the long-eared owl and the little owl; there have also been isolated sightings of the bearded owl.
– The tawny owl is a characteristic species of owl for this particular forest. Why? The tawny owl is a bird that nests in hollow trees. A tree usually becomes hollow as it ages; its branches fall away, and a hollow forms. And in this forest there are many old trees, especially ancient oaks. A tree is considered ancient after it has lived for 100 years or more.
The little owl is more commonly found on the forest’s edge, as it prefers to be closer to human dwellings. The long-eared owl, on the other hand, favours spruce trees; the researchers had hoped to hear or see one, but this time they were unsuccessful.
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The auditory provocation method
During the census, the acoustic provocation method is used. At specific points along the route, a recording of an owl’s call is played. If there are other owls nearby, they may respond to the call. Based on the response, experts determine the species, sex and approximate location of the bird.
Incidentally, you can also count owls by their pellets (the little balls of food that owls regurgitate). But to do this, you need to know exactly where the nest is. This also allows you to work out what the owl has been hunting.
– An owl may, at best, be with a mate, but if it hears a rival, it becomes stressed because it needs to chase the rival away. This is an artificially induced stress for the bird. And if there is no mate, it’s even worse: the owl then flies about trying to find where its mate has gone, instead of attending to matters vital for its survival.
That is why each route is flown only once during a single season. They are planned carefully so as not to cause unnecessary stress to the birds.
This season’s results
During the most recent survey, researchers recorded seven tawny owls — two males and five females. In total, more than 16 individuals have already been counted this season in various parts of Holosiivskyi Forest. All the birds recorded belong to the species Strix aluco, which remains one of the key nocturnal predators in this urban forest ecosystem.
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